Internet DRAFT - draft-ietf-sipping-basic-call-flows

draft-ietf-sipping-basic-call-flows





   SIPPING Working Group                                    A. Johnston 
   Internet Draft                                              WorldCom 
   Document:                                                 S. Donovan 
    draft-ietf-sipping-basic-call-flows-02.txt                R. Sparks 
   Expires: October 2003                                  C. Cunningham 
                                                            dynamicsoft 
                                                             K. Summers 
                                                                  Sonus 
                                                             April 2003 
    
    
           Session Initiation Protocol Basic Call Flow Examples 
    
    
Status of this Memo 
    
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026.  
    
   Internet-Drafts are working documents of the Internet Engineering 
   Task Force (IETF), its areas, and its working groups.  Note that      
   other groups may also distribute working documents as Internet-
   Drafts. 
    
   Internet-Drafts are draft documents valid for a maximum of six months 
   and may be updated, replaced, or obsoleted by other documents at any 
   time.  It is inappropriate to use Internet-Drafts as reference 
   material or to cite them other than as "work in progress." 
    
   The list of current Internet-Drafts can be accessed at 
        http://www.ietf.org/ietf/1id-abstracts.txt 
   The list of Internet-Draft Shadow Directories can be accessed at 
        http://www.ietf.org/shadow.html. 
    
    
Abstract 
    
   This informational document gives examples of Session Initiation 
   Protocol (SIP) call flows.  Elements in these call flows include SIP 
   User Agents and Clients, SIP Proxy and Redirect Servers.  Scenarios 
   include SIP Registration and SIP session establishment.  Call flow 
   diagrams and message details are shown.    
    
    
Conventions used in this document 
    
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this 
   document are to be interpreted as described in RFC-2119. 
    
 
 
Johnston et al          Expires - October 2003                [Page 1] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
Table of Contents 
    
   1. Overview.......................................................2 
      1.1 General Assumptions........................................3 
      1.2 Legend for Message Flows...................................3 
      1.3 SIP Protocol Assumptions...................................3 
   2. SIP Registration...............................................5 
      2.1 Successful New Registration................................5 
      2.2 Update of Contact List.....................................7 
      2.3 Request for Current Contact List...........................9 
      2.4 Cancellation of Registration..............................11 
      2.5 Unsuccessful Registration.................................13 
   3. SIP Session Establishment.....................................15 
      3.1 Successful Session Establishment..........................15 
      3.2 Session Establishment Through Two Proxies.................18 
      3.3 Session with Multiple Proxy Authentication................29 
      3.4 Successful Session with Proxy Failure.....................40 
      3.5 Session Through a SIP ALG.................................49 
      3.6 Session via Redirect and Proxy Servers with SDP in ACK....57 
      3.7 Session with re-INVITE (IP Address Change)................64 
      3.8 Unsuccessful No Answer....................................70 
      3.9 Unsuccessful Busy.........................................78 
      3.10 Unsuccessful No Response from User Agent.................83 
      3.11 Unsuccessful Temporarily Unavailable.....................88 
   Security Considerations..........................................93 
   Normative References.............................................94 
   Informative References...........................................94 
   Acknowledgments..................................................94 
   Author's Addresses...............................................95 
    
1.   Overview 
    
   The call flows shown in this document were developed in the design of 
   a SIP IP communications network.  They represent an example 
   minimum set of functionality. 
    
   It is the hope of the authors that this document will be useful for 
   SIP implementers, designers, and protocol researchers alike and will 
   help further the goal of a standard implementation of RFC 3261[1].  
   These flows represent carefully checked and working group reviewed 
   scenarios of the most basic examples as a companion to the 
   specifications. 
    
   These call flows are based on the current version 2.0 of SIP in 
   RFC 3261[i] with SDP usage described in RFC 3264[ii]. Other RFCs also 
   comprise the SIP standard but are not used in this set of basic call 
   flows. 
    

 
 
Johnston et al          Expires  October 2003                [Page 2] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Call flow examples of SIP interworking with the PSTN through gateways 
   are contained in a companion document, RFC xxxx[4]. 
    
 1.1 General Assumptions 
    
   A number of architecture, network, and protocol assumptions underlie 
   the call flows in this document. Note that these assumptions are not 
   requirements.  They are outlined in this section so that they may be 
   taken into consideration and to aid in the understanding of the call 
   flow examples. 
    
   The authentication of SIP User Agents in these example call flows is 
   performed using HTTP Digest as defined in [1] and [iii].   
    
   Some Proxy Servers in these call flows insert Record-Route headers 
   into requests to ensure that they are in the signaling path for 
   future message exchanges.   
    
   These flows show TCP, TLS, and UDP for transport.  See the discussion 
   in RFC 3261 for details on the transport issues for SIP.   
 
 1.2 Legend for Message Flows 
    
   Dashed lines (---) represent signaling messages that are mandatory to 
   the call scenario. These messages can be SIP or PSTN 
   signaling.  The arrow indicates the direction of message flow. 
    
   Double dashed lines (===) represent media paths between network 
   elements. 
    
   Messages with parentheses around their name represent optional 
   messages. 
    
   Messages are identified in the Figures as F1, F2, etc.  This 
   references the message details in the list that follows the Figure. 
   Comments in the message details are shown in the following form: 
    
    /* Comments. */ 
    
 1.3 SIP Protocol Assumptions 
    
   This document does not prescribe the flows precisely as they are 
   shown, but rather the flows illustrate the principles for best 
   practice.  They are best practices usages (orderings, syntax, 
   selection of features for the purpose, handling of error) of SIP 
   methods, headers and parameters.  IMPORTANT: The exact flows here 
   must not be copied as is by an implementer due to specific incorrect 
   characteristics that were introduced into the document for 
   convenience and are listed below.  To sum up, the basic flows 
 
 
Johnston et al          Expires  October 2003                [Page 3] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   represent well-reviewed examples of SIP usage, which are best common 
   practice according to IETF consensus. 
    
   For simplicity in reading and editing the document, there are a 
   number of differences between some of the examples and actual SIP 
   messages.  For example, the HTTP Digest responses are not actual MD5 
   encodings.  Call-IDs are often repeated, and CSeq counts often begin 
   at 1.  Header fields are usually shown in the same order.  Usually 
   only the minimum required header field set is shown, others that 
   would normally be present such as Accept, Supported, Allow, etc are 
   not shown. 
    
   Actors: 
    
   Element       Display Name   URI                         IP Address 
   -------       ------------   ---                         ---------- 
    
   User Agent    Alice          alice@atlanta.example.com   192.0.2.10 
   User Agent    Bob            bob@biloxi.example.com      192.0.2.201 
   User Agent                   bob@chicago.example.com     192.0.2.100 
   Proxy Server                 ss1.atlanta.example.com     192.0.2.111 
   Proxy/Registrar              ss2.biloxi.example.com      192.0.2.222 
   Proxy Server                 ss3.chicago.example.com     192.0.2.233 
   ALG                          alg1.atlanta.example.com    192.0.2.128 
                                                          
    























 
 
Johnston et al          Expires  October 2003                [Page 4] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
2.   SIP Registration 
    
   Registration binds a particular device Contact URI with a SIP user 
   Address of Record (AOR).  
    
 2.1 Successful New Registration 
    
    Bob                        SIP Server 
     |                               | 
     |          REGISTER F1          | 
     |------------------------------>| 
     |      401 Unauthorized F2      | 
     |<------------------------------| 
     |          REGISTER F3          | 
     |------------------------------>| 
     |            200 OK F4          | 
     |<------------------------------| 
     |                               | 
    
   Bob sends a SIP REGISTER request to the SIP server.  The request 
   includes the user's contact list.  This flow shows the use of HTTP 
   Digest for authentication using TLS transport.  TLS transport is used 
   due to the lack of integrity protection in HTTP Digest and the danger 
   of registration hijacking without it, as described in RFC 3261 [1].  
   The SIP server provides a challenge to Bob.  Bob enters her/his valid 
   user ID and password.  Bob's SIP client encrypts the user information 
   according to the challenge issued by the SIP server and sends the 
   response to the SIP server.  The SIP server validates the user's 
   credentials.  It registers the user in its contact database and 
   returns a response (200 OK) to Bob's SIP client.  The response 
   includes the user's current contact list in Contact headers.  The 
   format of the authentication shown is HTTP digest.  It is assumed 
   that Bob has not previously registered with this Server. 
    
    
   Message Details 
    
    
   F1 REGISTER Bob -> SIP Server 
    
   REGISTER sips:ss2.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com> 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   Contact: <sips:bob@client.biloxi.example.com> 
 
 
Johnston et al          Expires  October 2003                [Page 5] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Length: 0 
    
    
   F2 401 Unauthorized SIP Server -> Bob 
    
   SIP/2.0 401 Unauthorized 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com>;tag=1410948204 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth", 
    nonce="ea9c8e88df84f1cec4341ae6cbe5a359", 
    opaque="", stale=FALSE, algorithm=MD5 
   Content-Length: 0 
    
    
   F3 REGISTER Bob -> SIP Server 
    
   REGISTER sips:ss2.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   From: Bob <sips:bob@biloxi.example.com>;tag=ja743ks76zlflH 
   To: Bob <sips:bob@biloxi.example.com> 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 2 REGISTER 
   Contact: <sips:bob@client.biloxi.example.com> 
   Authorization: Digest username="bob", realm="atlanta.example.com" 
    nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="", 
    uri="sips:ss2.biloxi.example.com", 
    response="dfe56131d1958046689d83306477ecc" 
   Content-Length: 0 
    
    
   F4 200 OK SIP Server -> Bob 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sips:bob@biloxi.example.com>;tag=ja743ks76zlflH 
   To: Bob <sips:bob@biloxi.example.com>;tag=37GkEhwl6 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 2 REGISTER 
   Contact: <sips:bob@client.biloxi.example.com>;expires=3600 
   Content-Length: 0  



 
 
Johnston et al          Expires  October 2003                [Page 6] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
 2.2 Update of Contact List 
    
    
   Bob                        SIP Server 
     |                               | 
     |          REGISTER F1          | 
     |------------------------------>| 
     |            200 OK F2          | 
     |<------------------------------| 
     |                               | 
    
    
   Bob wishes to update the list of addresses where the SIP server 
   will redirect or forward INVITE requests. 
    
   Bob sends a SIP REGISTER request to the SIP server.  Bob's 
   request includes an updated contact list.  Since the user already has 
   authenticated with the server, the user supplies authentication 
   credentials with the request and is not challenged by the server. 
   The SIP server validates the user's credentials.  It registers the 
   user in its contact database, updates the user's contact list, and 
   returns a response (200 OK) to Bob's SIP client.  The response 
   includes the user's current contact list in Contact headers. 
    
   Message Details 
    
    
   F1 REGISTER Bob -> SIP Server 
    
   REGISTER sips:ss2.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com> 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   Contact: mailto:bob@biloxi.example.com 
   Authorization: Digest username="bob", realm="atlanta.example.com",  
    qop="auth", nonce="1cec4341ae6cbe5a359ea9c8e88df84f", opaque="", 
    uri="sips:ss2.biloxi.example.com", 
    response="71ba27c64bd01de719686aa4590d5824" 
   Content-Length: 0 
    
    
   F2 200 OK SIP Server -> Bob 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
 
 
Johnston et al          Expires  October 2003                [Page 7] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    ;received=192.0.2.201 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com>;tag=34095828jh 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   Contact: <sips:bob@client.biloxi.example.com>;expires=3600 
   Contact: <mailto:bob@biloxi.example.com>;expires=4294967295 
   Content-Length: 0 
    
    
    
    
    
    
    
    
    
    
    
    





























 
 
Johnston et al          Expires  October 2003                [Page 8] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
     
 2.3 Request for Current Contact List 
    
    
   Bob                        SIP Server 
     |                               | 
     |          REGISTER F1          | 
     |------------------------------>| 
     |            200 OK F2          | 
     |<------------------------------| 
     |                               | 
    
   Bob sends a register request to the Proxy Server containing no 
   Contact headers, indicating the user wishes to query the server for 
   the user's current contact list.  Since the user already has 
   authenticated with the server, the user supplies authentication 
   credentials with the request and is not challenged by the server. The 
   SIP server validates the user's credentials.  The server returns a 
   response (200 OK) which includes the user's current registration list 
   in Contact headers. 
    
    
   Message Details 
    
   F1 REGISTER Bob -> SIP Server 
    
   REGISTER sips:ss2.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com> 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   Authorization: Digest username="bob", realm="atlanta.example.com", 
    nonce="df84f1cec4341ae6cbe5ap359a9c8e88", opaque="", 
    uri="sips:ss2.biloxi.example.com", 
    response="aa7ab4678258377c6f7d4be6087e2f60" 
   Content-Length: 0 
    
    
   F2 200 OK SIP Server -> Bob 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com>;tag=jqoiweu75 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
 
 
Johnston et al          Expires  October 2003                [Page 9] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Contact: <sips:bob@client.biloxi.example.com>;expires=3600 
   Contact: <mailto:bob@biloxi.example.com>;expires=4294967295 
   Content-Length: 0  














































 
 
Johnston et al          Expires  October 2003               [Page 10] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
 2.4 Cancellation of Registration 
    
   Bob                         SIP Server 
     |                               | 
     |          REGISTER F1          | 
     |------------------------------>| 
     |            200 OK F2          | 
     |<------------------------------| 
     |                               | 
    
   Bob wishes to cancel their registration with the SIP 
   server. Bob sends a SIP REGISTER request to the 
   SIP server.  The request has an expiration period of 0 and applies to 
   all existing contact locations.  Since the user already has 
   authenticated with the server, the user supplies authentication 
   credentials with the request and is not challenged by the server. 
   The SIP server validates the user's credentials.  It clears the 
   user's contact list, and returns a response (200 OK) to Bob's SIP 
   client. 
    
   Message Details 
    
    
   F1 REGISTER Bob -> SIP Server 
    
   REGISTER sips:ss2.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com> 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   Expires: 0 
   Contact: * 
   Authorization: Digest username="bob", realm="atlanta.example.com", 
    nonce="88df84f1cac4341aea9c8ee6cbe5a359", opaque="", 
    uri="sips:ss2.biloxi.example.com", 
    response="ff0437c51696f9a76244f0cf1dbabbea" 
   Content-Length: 0 
    
    
   F2 200 OK SIP Server -> Bob 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com>;tag=1418nmdsrf 
 
 
Johnston et al          Expires  October 2003               [Page 11] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   Content-Length: 0 














































 
 
Johnston et al          Expires  October 2003               [Page 12] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
 2.5 Unsuccessful Registration 
    
   Bob                        SIP Server 
     |                               | 
     |          REGISTER F1          | 
     |------------------------------>| 
     |      401 Unauthorized F2      | 
     |<------------------------------| 
     |          REGISTER F3          | 
     |------------------------------>| 
     |      401 Unauthorized F4      | 
     |<------------------------------| 
     |                               | 
    
    
    
   Bob sends a SIP REGISTER request to the SIP Server.  The SIP 
   server provides a challenge to Bob.  Bob enters her/his user ID 
   and password.  Bob's SIP client encrypts the user information 
   according to the challenge issued by the SIP server and sends the 
   response to the SIP server.  The SIP server attempts to validate the 
   user's credentials, but they are not valid (the user's password does 
   not match the password established for the user's account).  The 
   server returns a response (401 Unauthorized) to Bob's SIP client. 
    
    
    
   Message Details 
    
    
   F1 REGISTER Bob -> SIP Server 
    
   REGISTER sips:ss2.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com> 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   Contact: <sips:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F2 Unauthorized SIP Server -> Bob 
    
   SIP/2.0 401 Unauthorized 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
 
 
Johnston et al          Expires  October 2003               [Page 13] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl 
   To: Bob <sips:bob@biloxi.example.com>;tag=1410948204 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 1 REGISTER 
   WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth",  
    nonce="f1cec4341ae6ca9c8e88df84be55a359",  
    opaque="", stale=FALSE, algorithm=MD5 
   Content-Length: 0 
    
    
   F3 REGISTER Bob -> SIP Server 
    
   REGISTER sips:ss2.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   From: Bob <sips:bob@biloxi.example.com>;tag=JueHGuidj28dfga 
   To: Bob <sips:bob@biloxi.example.com> 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 2 REGISTER 
   Contact: <sips:bob@client.biloxi.example.com> 
   Authorization: Digest username="bob", realm="atlanta.example.com", 
    nonce="f1cec4341ae6ca9c8e88df84be55a359", opaque="", 
    uri="sips:ss2.biloxi.example.com", 
    response="61f8470ceb87d7ebf508220214ed438b" 
   Content-Length: 0 
    
    
   /*  The response above encodes the incorrect password */ 
    
   F4 401 Unauthorized SIP Server -> Bob 
    
   SIP/2.0 401 Unauthorized 
   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sips:bob@biloxi.example.com>;tag=JueHGuidj28dfga 
   To: Bob <sips:bob@biloxi.example.com>;tag=1410948204 
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com 
   CSeq: 2 REGISTER 
   WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth", 
    nonce="84f1c1ae6cbe5ua9c8e88dfa3ecm3459", 
    opaque="", stale=FALSE, algorithm=MD5 
   Content-Length: 0 
    






 
 
Johnston et al          Expires  October 2003               [Page 14] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
3.    SIP Session Establishment 
    
   This section details session establishment between two SIP User 
   Agents (UAs): Alice and Bob.  Alice (sip:alice@atlanta.example.com) 
   and Bob (sip:bob@biloxi.example.com) are assumed to be SIP phones or 
   SIP-enabled devices.  The successful calls show the initial 
   signaling, the exchange of media information in the form of SDP 
   payloads, the establishment of the media session, then finally the 
   termination of the call. 
    
   HTTP Digest authentication is used by Proxy Servers to authenticate 
   the caller Alice. It is assumed that Bob has registered with Proxy 
   Server Proxy 2 as per Section 2 to be able to receive the calls via 
   the Proxy. 
    
 3.1 Successful Session Establishment 
    
   Alice                     Bob 
     |                        | 
     |       INVITE F1        | 
     |----------------------->| 
     |    180 Ringing F2      | 
     |<-----------------------| 
     |                        | 
     |       200 OK F3        | 
     |<-----------------------| 
     |         ACK F4         | 
     |----------------------->| 
     |   Both Way RTP Media   | 
     |<======================>| 
     |                        | 
     |         BYE F5         | 
     |<-----------------------| 
     |       200 OK F6        | 
     |----------------------->| 
     |                        | 
    
   In this scenario, Alice completes a call to Bob directly. 
    
    
   Message Details 
    
    
   F1 INVITE Alice -> Bob 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
 
 
Johnston et al          Expires  October 2003               [Page 15] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F2 180 Ringing Bob -> Alice 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=8321234356 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com;transport=tcp> 
   Content-Length: 0 
    
    
   F3 200 OK Bob -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=8321234356 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
 
 
Johnston et al          Expires  October 2003               [Page 16] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   a=rtpmap:0 PCMU/8000 
    
    
   F4 ACK Alice -> Bob 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bd5 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=8321234356 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   /* RTP streams are established between Alice and Bob */ 
    
   /* Bob Hangs Up with Alice. Note that the CSeq is NOT 2, since  
      Alice and Bob maintain their own independent CSeq counts.  
      (The INVITE was request 1 generated by Alice, and the BYE is 
      request 1 generated by Bob) */ 
    
   F5 BYE Bob -> Alice 
    
   BYE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   From: Bob <sip:bob@biloxi.example.com>;tag=8321234356 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F6 200 OK Alice -> Bob 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sip:bob@biloxi.example.com>;tag=8321234356 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 





 
 
Johnston et al          Expires  October 2003               [Page 17] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
 3.2 Session Establishment Through Two Proxies 
    
   Alice           Proxy 1          Proxy 2            Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|                |                | 
     |     407 F2     |                |                | 
     |<---------------|                |                | 
     |     ACK F3     |                |                | 
     |--------------->|                |                | 
     |   INVITE F4    |                |                | 
     |--------------->|   INVITE F5    |                | 
     |     100  F6    |--------------->|   INVITE F7    | 
     |<---------------|     100  F8    |--------------->| 
     |                |<---------------|                | 
     |                |                |     180 F9     | 
     |                |    180 F10     |<---------------| 
     |     180 F11    |<---------------|                | 
     |<---------------|                |     200 F12    | 
     |                |    200 F13     |<---------------| 
     |     200 F14    |<---------------|                | 
     |<---------------|                |                | 
     |     ACK F15    |                |                | 
     |--------------->|    ACK F16     |                | 
     |                |--------------->|     ACK F17    | 
     |                |                |--------------->| 
     |                Both Way RTP Media                | 
     |<================================================>| 
     |                |                |     BYE F18    | 
     |                |    BYE F19     |<---------------| 
     |     BYE F20    |<---------------|                | 
     |<---------------|                |                | 
     |     200 F21    |                |                | 
     |--------------->|     200 F22    |                | 
     |                |--------------->|     200 F23    | 
     |                |                |--------------->| 
     |                |                |                | 
    
   In this scenario, Alice completes a call to Bob using two proxies 
   Proxy 1 and Proxy 2.  The initial INVITE (F1) contains a pre-loaded 
   Route header with the address of Proxy 1 (Proxy 1 is configured as a 
   default outbound proxy for Alice).  The request does not contain the 
   Authorization credentials Proxy 1 requires, so a 407 Proxy 
   Authorization response is sent containing the challenge information. 
   A new INVITE (F4) is then sent containing the correct credentials and 
   the call proceeds.  The call terminates when Bob disconnects by 
   initiating a BYE message. 
    
 
 
Johnston et al          Expires  October 2003               [Page 18] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Proxy 1 inserts a Record-Route header into the INVITE message to 
   ensure that it is present in all subsequent message exchanges.  Proxy 
   2 also inserts itself into the Record-Route header.  The ACK (F15) 
   and BYE (F18) both have a Route header. 
    
    
   Message Details 
    
    
   F1 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Proxy 1 challenges Alice for authentication */ 
    
   F2 407 Proxy Authorization Required Proxy 1 -> Alice 
    
   SIP/2.0 407 Proxy Authorization Required 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=3flal12sf 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 INVITE 
   Proxy-Authenticate: Digest realm="atlanta.example.com", qop="auth",  
    nonce="f84f1cec41e6cbe5aea9c8e88d359", 
    opaque="", stale=FALSE, algorithm=MD5 
   Content-Length: 0 
    
    
 
 
Johnston et al          Expires  October 2003               [Page 19] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   F3 ACK Alice -> Proxy 1 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=3flal12sf 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   /* Alice responds be re-sending the INVITE with authentication 
      credentials in it. */ 
    
   F4 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Proxy-Authorization: Digest username="alice", 
    realm="atlanta.example.com", 
    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="42ce3cef44b22f50c6a6071bc8" 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Proxy 1 accepts the credentials and forwards the INVITE to Proxy 
   2.  Client for Alice prepares to receive data on port 49172 from the 
   network. */ 
    
   F5 INVITE Proxy 1 -> Proxy 2 
    
 
 
Johnston et al          Expires  October 2003               [Page 20] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F6 100 Trying Proxy 1 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 INVITE 
   Content-Length: 0 
    
    
   F7 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 68 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
 
 
Johnston et al          Expires  October 2003               [Page 21] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F8 100 Trying Proxy 2 -> Proxy 1 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 INVITE 
   Content-Length: 0 
    
    
   F9 180 Ringing Bob -> Proxy 2 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   Contact: <sip:bob@client.biloxi.example.com;transport=tcp> 
   CSeq: 2 INVITE 
   Content-Length: 0 
    
    
 
 
Johnston et al          Expires  October 2003               [Page 22] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   F10 180 Ringing Proxy 2 -> Proxy 1 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   Contact: <sip:bob@client.biloxi.example.com;transport=tcp> 
   CSeq: 2 INVITE 
   Content-Length: 0 
    
    
   F11 180 Ringing Proxy 1 -> Alice 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   Contact: <sip:bob@client.biloxi.example.com;transport=tcp> 
   CSeq: 2 INVITE 
   Content-Length: 0 
    
    
   F12 200 OK Bob -> Proxy 2 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.biloxi.example.com;transport=tcp> 
 
 
Johnston et al          Expires  October 2003               [Page 23] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F13 200 OK Proxy 2 -> Proxy 1 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.biloxi.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F14 200 OK Proxy 1 -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 INVITE 
 
 
Johnston et al          Expires  October 2003               [Page 24] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Contact: <sip:bob@client.biloxi.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F15 ACK Alice -> Proxy 1 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr>, 
    <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 ACK 
   Content-Length: 0 
    
    
   F16 ACK Proxy 1 -> Proxy 2 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Route: <sip:ss2.biloxi.example.com;lr>  
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 ACK 
   Content-Length: 0 
    
    
   F17 ACK Proxy 2 -> Bob 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
 
 
Johnston et al          Expires  October 2003               [Page 25] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76 
    ;received=192.0.2.101 
   Max-Forwards: 68 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 2 ACK 
   Content-Length: 0 
    
    
   /* RTP streams are established between Alice and Bob */ 
    
   /* Bob Hangs Up with Alice. */ 
    
   /* Again, note that the CSeq is NOT 3.  Alice and Bob maintain 
      their own separate CSeq counts */ 
    
   F18 BYE Bob -> Proxy 2 
    
   BYE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F19 BYE Proxy 2 -> Proxy 1 
    
   BYE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   Max-Forwards: 69 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F20 BYE Proxy 1 -> Alice 
    
 
 
Johnston et al          Expires  October 2003               [Page 26] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   BYE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   Max-Forwards: 68 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F21 200 OK Alice -> Proxy 1 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F22 200 OK Proxy 1 -> Proxy 2 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.101 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F23 200 OK Proxy 2 -> Bob 
    
 
 
Johnston et al          Expires  October 2003               [Page 27] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 3848276298220188511@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
     







































 
 
Johnston et al          Expires  October 2003               [Page 28] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
 3.3 Session with Multiple Proxy Authentication 
    
     Alice        Proxy 1     Proxy 2         Bob 
       |            |           |             | 
       |  INVITE F1 |           |             | 
       |----------->|           |             | 
       |  407 Proxy Authorization Required F2 | 
       |<-----------|           |             | 
       |   ACK F3   |           |             | 
       |----------->|           |             | 
       |  INVITE F4 |           |             | 
       |----------->|           |             | 
       |   100 F5   |           |             | 
       |<-----------| INVITE F6 |             | 
       |            |---------->|             | 
       |            |  407 Proxy Authorization Required F7  
       |            |<----------|             | 
       |            |   ACK F8  |             | 
       |            |---------->|             | 
       |  407 Proxy Authorization Required F9 | 
       |<-----------|           |             | 
       |   ACK F10  |           |             | 
       |----------->|           |             | 
       |  INVITE F11|           |             | 
       |----------->|           |             | 
       |   100 F12  |           |             | 
       |<-----------| INVITE F13|             | 
       |            |---------->|             | 
       |            |  100 F14  |             | 
       |            |<----------|  INVITE F15 | 
       |            |           |------------>| 
       |            |           | 200 OK F16  | 
       |            | 200 OK F17|<------------| 
       | 200 OK F18 |<----------|             | 
       |<-----------|           |             | 
       |   ACK F19  |           |             | 
       |----------->|  ACK F20  |             | 
       |            |---------->|   ACK F21   | 
       |            |           |------------>| 
       |           RTP Media Path             | 
       |<====================================>| 
    
   In this scenario, Alice completes a call to Bob using two proxies 
   Proxy 1 and Proxy 2.  Alice has valid credentials in both domains. 
   Since the initial INVITE (F1) does not contain the 
   Authorization credentials Proxy 1 requires, so a 407 Proxy 
   Authorization response is sent containing the challenge information. 
   A new INVITE (F4) is then sent containing the correct credentials and 
 
 
Johnston et al          Expires  October 2003               [Page 29] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   the call proceeds after Proxy 2 challenges and receives valid 
   credentials.  The call terminates when Bob disconnects by 
   initiating a BYE message. 
    
   Proxy 1 inserts a Record-Route header into the INVITE message to 
   ensure that it is present in all subsequent message exchanges.  Proxy 
   2 also inserts itself into the Record-Route header.   
    
    
    
   Message Details 
    
    
   F1 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Proxy 1 challenges Alice for authentication */ 
    
   F2 407 Proxy Authorization Required Proxy 1 -> Alice 
    
   SIP/2.0 407 Proxy Authorization Required 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=876321 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Proxy-Authenticate: Digest realm="atlanta.example.com", qop="auth", 
    nonce="wf84f1cczx41ae6cbeaea9ce88d359", 
 
 
Johnston et al          Expires  October 2003               [Page 30] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    opaque="", stale=FALSE, algorithm=MD5 
   Content-Length: 0 
    
    
   F3 ACK Alice -> Proxy 1 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Max-Forwards: 70 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=876321 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   /* Alice responds be re-sending the INVITE with authentication 
      credentials in it.  The same Call-ID is used, so the CSeq is  
      increased. */ 
    
   F4 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Proxy-Authorization: Digest username="alice", 
    realm="atlanta.example.com", 
    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="42ce3cef44b22f50c6a6071bc8" 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Proxy 1 accepts the credentials and forwards the INVITE to Proxy 
 
 
Johnston et al          Expires  October 2003               [Page 31] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   2.  Client for Alice prepares to receive data on port 49172 from the 
   network. */ 
    
   F5 100 Trying Proxy 1 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE  
   Content-Length: 0 
    
    
   F6 INVITE Proxy 1 -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Proxy 2 challenges Alice for authentication */ 
    
   F7 407 Proxy Authorization Required Proxy 2 -> Proxy 1 
    
   SIP/2.0 407 Proxy Authorization Required 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21 
    ;received=192.0.2.101 
 
 
Johnston et al          Expires  October 2003               [Page 32] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=838209 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth", 
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", 
    opaque="", stale=FALSE, algorithm=MD5 
   Content-Length: 0 
    
    
   F8 ACK Proxy 1 -> Proxy 2 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=838209 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 ACK 
   Content-Length: 0 
    
    
   /* Proxy 1 forwards the challenge to Alice for authentication from 
   Proxy 2 */ 
    
   F9 407 Proxy Authorization Required Proxy 1 -> Alice 
    
   SIP/2.0 407 Proxy Authorization Required 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=838209 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth", 
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", 
    opaque="", stale=FALSE, algorithm=MD5 
   Content-Length: 0 
    
    
   F10 ACK Alice -> Proxy 1 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=838209 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 ACK 
 
 
Johnston et al          Expires  October 2003               [Page 33] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Proxy-Authorization: Digest username="alice", 
    realm="atlanta.example.com", 
    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="42ce3cef44b22f50c6a6071bc8" 
   Content-Length: 0 
    
    
   /* Alice responds be re-sending the INVITE with authentication 
   credentials for Proxy 1 AND Proxy 2.  */ 
    
   F11 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Proxy-Authorization: Digest username="alice", 
    realm="atlanta.example.com", 
    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="42ce3cef44b22f50c6a6071bc8" 
   Proxy-Authorization: Digest username="alice", 
    realm="biloxi.example.com", 
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8" 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Proxy 1 finds its credentials and authorizes Alice, forwarding the 
   INVITE to Proxy.  */ 
    
    
   F12 100 Trying Proxy 1 -> Alice 
    
   SIP/2.0 100 Trying 
 
 
Johnston et al          Expires  October 2003               [Page 34] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 INVITE 
   Content-Length: 0 
    
    
   F13 INVITE Proxy 1 -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Proxy-Authorization: Digest username="alice", 
    realm="biloxi.example.com", 
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8" 
   Content-Type: application/sdp 
   Content-Length: 151   
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Proxy 2 finds its credentials and authorizes Alice, forwarding the 
   INVITE to Bob.  */ 
    
   F14 100 Trying Proxy 2 -> Proxy 1 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
 
 
Johnston et al          Expires  October 2003               [Page 35] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 INVITE 
   Content-Length: 0 
    
    
   F15 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 68 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Bob answers the call immediately */ 
    
   F16 200 OK Bob -> Proxy 2 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=9103874 
 
 
Johnston et al          Expires  October 2003               [Page 36] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F17 200 OK Proxy 2 -> Proxy 1 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=9103874 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F18 200 OK Proxy 1 -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
 
 
Johnston et al          Expires  October 2003               [Page 37] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   To: Bob <sip:bob@biloxi.example.com>;tag=9103874 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F19 ACK Alice -> Proxy 1 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr>, 
    <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=9103874 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 ACK 
   Proxy-Authorization: Digest username="alice", 
    realm="atlanta.example.com", 
    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="42ce3cef44b22f50c6a6071bc8" 
   Proxy-Authorization: Digest username="alice", 
    realm="biloxi.example.com", 
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8" 
   Content-Length: 0 
    
    
   F20 ACK Proxy 1 -> Proxy 2 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Route: <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=9103874 
 
 
Johnston et al          Expires  October 2003               [Page 38] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 ACK 
   Contact: <sip:bob@client.biloxi.example.com> 
   Proxy-Authorization: Digest username="alice", 
    realm="biloxi.example.com", 
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="", 
    uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8" 
   Content-Length: 0 
    
    
   F21 ACK Proxy 2 -> Bob 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44 
    ;received=192.0.2.101 
   Max-Forwards: 68 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=9103874 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 3 ACK 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
     
  





















 
 
Johnston et al          Expires  October 2003               [Page 39] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
3.4 Successful Session with Proxy Failure 
    
   Alice           Proxy 1          Proxy 2            Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|                |                | 
     |   INVITE F2    |                |                | 
     |--------------->|                |                | 
     |   INVITE F3    |                |                | 
     |--------------->|                |                | 
     |   INVITE F4    |                |                | 
     |--------------->|                |                | 
     |   INVITE F5    |                |                | 
     |--------------->|                |                | 
     |   INVITE F6    |                |                | 
     |--------------->|                |                | 
     |   INVITE F7    |                |                | 
     |--------------->|                |                | 
     |     INVITE F8                   |                | 
     |-------------------------------->|                | 
     |            407 F9               |                | 
     |<--------------------------------|                | 
     |             ACK F10             |                | 
     |-------------------------------->|                | 
     |           INVITE F11            |                | 
     |-------------------------------->|   INVITE F12   | 
     |             100  F13            |--------------->| 
     |<--------------------------------|                | 
     |                                 |     180 F14    | 
     |             180 F15             |<---------------| 
     |<--------------------------------|                | 
     |                                 |     200 F16    | 
     |             200 F17             |<---------------| 
     |<--------------------------------|                | 
     |             ACK F18             |                | 
     |-------------------------------->|     ACK F19    | 
     |                                 |--------------->| 
     |                Both Way RTP Media                | 
     |<================================================>| 
     |                                 |     BYE F20    | 
     |             BYE F21             |<---------------| 
     |<--------------------------------|                | 
     |             200 F22             |                | 
     |-------------------------------->|     200 F23    | 
     |                                 |--------------->| 
     |                                 |                | 
    
    

 
 
Johnston et al          Expires  October 2003               [Page 40] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   In this scenario, Alice completes a call to Bob via a Proxy Server. 
   Alice is configured for a primary SIP Proxy Server Proxy 1 and a 
   secondary SIP Proxy Server Proxy 2 (Or is able to use DNS SRV records 
   to locate Proxy 1 and Proxy 2).  Alice has valid credentials for both 
   domains.  Proxy 1 is out of service and does not respond to INVITEs 
   (it is reachable, but unresponsive).  Alice then completes the call 
   to Bob using Proxy 2. 
    
    
   Message Details 
    
    
   F1 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK465b6d 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F2 INVITE Alice -> Proxy 1 
    
   Same as Message F1 
    
    
   F3 INVITE Alice -> Proxy 1 
    
   Same as Message F1 
    
    
   F4 INVITE Alice -> Proxy 1 
    
   Same as Message F1 
    
 
 
Johnston et al          Expires  October 2003               [Page 41] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
   F5 INVITE Alice -> Proxy 1 
    
   Same as Message F1 
    
    
   F6 INVITE Alice -> Proxy 1 
    
   Same as Message F1 
    
    
   F7 INVITE Alice -> Proxy 1 
    
   Same as Message F1 
    
    
   /* Alice gives up on the unresponsive proxy */ 
    
    
   F8 INVITE Alice -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Proxy 2 challenges Alice for authentication */ 
    
   F9 407 Proxy Authorization Required Proxy 2 -> Alice 
    
   SIP/2.0 407 Proxy Authorization Required 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
 
 
Johnston et al          Expires  October 2003               [Page 42] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   To: Bob <sip:bob@biloxi.example.com>;tag=2421452 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 1 INVITE 
   Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth", 
    nonce="1ae6cbe5ea9c8e8df84fqnlec434a359", 
    opaque="", stale=FALSE, algorithm=MD5 
   Content-Length: 0 
    
    
   F10 ACK Alice -> Proxy 2 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=2421452 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   /* Alice responds be re-sending the INVITE with authentication 
   credentials in it.  */ 
    
   F11 INVITE Alice -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Proxy-Authorization: Digest username="alice", 
    realm="biloxi.example.com", 
    nonce="1ae6cbe5ea9c8e8df84fqnlec434a359", opaque="", 
    uri="sip:bob@biloxi.example.com",  
    response="8a880c919d1a52f20a1593e228adf599" 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
 
 
Johnston et al          Expires  October 2003               [Page 43] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
    
   /* Proxy 2 accepts the credentials and forwards the INVITE to Bob. 
   Client for Alice prepares to receive data on port 49172 from the 
   network. 
   */ 
    
   F12 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F13 100 Trying Proxy 2 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 INVITE 
   Content-Length: 0 
    
    
   F14 180 Ringing Bob -> Proxy 2 
    
   SIP/2.0 180 Ringing 

 
 
Johnston et al          Expires  October 2003               [Page 44] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F15 180 Ringing Proxy 2 -> Alice 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F16 200 OK Bob -> Proxy 2 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
 
 
Johnston et al          Expires  October 2003               [Page 45] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F17 200 OK Proxy 2 -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F18 ACK Alice -> Proxy 2 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8g 
   Max-Forwards: 70 
   Route: <sip:ss2.biloxi.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 ACK 
   Content-Length: 0 
    
    
   F19 ACK Proxy 2 -> Bob 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8g 
    ;received=192.0.2.101 
   Max-Forwards: 69 
 
 
Johnston et al          Expires  October 2003               [Page 46] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 2 ACK 
   Content-Length: 0 
    
    
   /* RTP streams are established between Alice and Bob */ 
    
   /* Bob Hangs Up with Alice. */ 
    
   F20 BYE Bob -> Proxy 2 
    
   BYE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
   Max-Forwards: 70 
   Route: <sip:ss2.biloxi.example.com;lr> 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F21 BYE Proxy 2 -> Alice 
    
   BYE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   Max-Forwards: 69 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F22 200 OK Alice -> Proxy 2 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
 
 
Johnston et al          Expires  October 2003               [Page 47] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F23 200 OK Proxy 2 -> Bob 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7 
    ;received=192.0.2.201 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
    
    
    
    




























 
 
Johnston et al          Expires  October 2003               [Page 48] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
     
 3.5 Session Through a SIP ALG 
    
   Alice             ALG           Proxy 2            Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|   INVITE F2    |                | 
     |     100 F3     |--------------->|   INVITE F4    | 
     |<---------------|     100 F5     |--------------->| 
     |                |<---------------|      180 F6    | 
     |                |     180 F7     |<---------------| 
     |     180 F8     |<---------------|                | 
     |<---------------|                |      200 F9    | 
     |                |    200 F10     |<---------------| 
     |     200 F11    |<---------------|                | 
     |<---------------|                                 | 
     |     ACK F12    |                                 | 
     |--------------->|             ACK F13             | 
     |                |-------------------------------->|      
     |    RTP Media   |        Both Way RTP Media       | 
     |<==============>|<===============================>| 
     |     BYE F14    |                                 | 
     |--------------->|             BYE F15             | 
     |                |-------------------------------->|   
     |                |             200 F16             | 
     |     200 F17    |<--------------------------------| 
     |<---------------|                                 | 
     |                |                                 | 
    
   Alice completes a call to Bob through a ALG (Application Layer 
   Gateway) and a SIP Proxy.  The routing through the ALG is 
   accomplished using a pre-loaded Route header in the INVITE F1. Note 
   that the media stream setup is not end-to-end - the ALG terminates 
   both media streams and bridges them.  This is done by the ALG 
   modifying the SDP in the INVITE (F1) and 200 OK (F10) messages, and 
   possibly any 18x or ACK messages containing SDP. 
    
   In addition to firewall traversal, this Back-to-Back User Agent 
   (B2BUA) could be used as part of an anonymizer 
   service (in which all identifying information on Alice would be 
   removed), or to perform codec media conversion, such as mu-law to A- 
   law conversion of PCM on an international call. 
    
   Also note that Proxy 2 does not Record-Route in this call flow. 
    
   Message Details 
    
    
 
 
Johnston et al          Expires  October 2003               [Page 49] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   F1 INVITE Alice -> SIP ALG 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Route: <sip:alg1.atlanta.example.com;lr> 
   Proxy-Authorization: Digest username="alice", 
    realm="biloxi.example.com", 
    nonce="85b4f1cen4341ae6cbe5a3a9c8e88df9", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="b3f392f9218a328b9294076d708e6815" 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* Client for Alice prepares to receive data on port 49172 from the 
   network. */ 
    
   F2 INVITE SIP ALG -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Proxy-Authorization: Digest username="alice", 
    realm="biloxi.example.com", 
    nonce="85b4f1cen4341ae6cbe5a3a9c8e88df9", opaque="", 
    uri="sip:bob@biloxi.example.com",  
    response="b3f392f9218a328b9294076d708e6815" 
 
 
Johnston et al          Expires  October 2003               [Page 50] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Type: application/sdp 
   Content-Length: 150 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.128 
   t=0 0 
   m=audio 2000 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F3 100 Trying SIP ALG -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   /* SIP ALG prepares to proxy data from port 192.0.2.128/2000 to 
   192.0.2.101/49172.   Proxy 2 uses a Location Service function to 
   determine where Bob is located. Based upon location analysis the call 
   is forwarded to Bob */ 
    
   F4 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
    ;received=192.0.2.128 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 68 
   Record-Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 150 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
 
 
Johnston et al          Expires  October 2003               [Page 51] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   s=- 
   c=IN IP4 192.0.2.128 
   t=0 0 
   m=audio 2000 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F5 100 Trying Proxy 2 -> SIP ALG 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
    ;received=192.0.2.128 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F6 180 Ringing Bob -> Proxy 2 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
    ;received=192.0.2.128 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F7 180 Ringing Proxy 2 -> SIP ALG 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
    ;received=192.0.2.128 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
 
 
Johnston et al          Expires  October 2003               [Page 52] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F8 180 Ringing SIP ALG -> Alice 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F9 200 OK Bob -> Proxy 2 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
    ;received=192.0.2.128 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F10 200 OK Proxy 2 -> SIP ALG 
    
 
 
Johnston et al          Expires  October 2003               [Page 53] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
    ;received=192.0.2.128 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F11 200 OK SIP ALG -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.128 
   t=0 0 
   m=audio 1734 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* The ALG prepares to proxy packets from 192.0.2.128/ 
      1734 to 192.0.2.201/3456 */ 
    
 
 
Johnston et al          Expires  October 2003               [Page 54] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   F12 ACK Alice -> SIP ALG 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bhh 
   Max-Forwards: 70 
   Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F13 ACK SIP ALG -> Bob 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bhh 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   /* RTP streams are established between Alice and the ALG and 
   between the ALG and B*/ 
    
   /* Alice Hangs Up with Bob. */ 
    
   F14 BYE Alice -> SIP ALG 
    
   BYE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5 
   Max-Forwards: 70 
   Route: <sip:alg1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 BYE 
   Content-Length: 0 
    
    
   F15 BYE SIP ALG -> Bob 
    
   BYE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
 
 
Johnston et al          Expires  October 2003               [Page 55] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 BYE 
   Content-Length: 0 
    
    
    
   F16 200 OK Bob -> SIP ALG 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1 
    ;received=192.0.2.128 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 BYE 
   Content-Length: 0 
    
    
   F17 200 OK SIP ALG -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 BYE 
   Content-Length: 0 
    
    
    
    
    
    
    







 
 
Johnston et al          Expires  October 2003               [Page 56] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
     
 3.6 Session via Redirect and Proxy Servers with SDP in ACK 
    
   Alice        Redirect Server     Proxy 3             Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|                |                | 
     |     302 F2     |                |                | 
     |<---------------|                |                | 
     |     ACK F3     |                |                | 
     |--------------->|                |                | 
     |     INVITE F4                   |                | 
     |-------------------------------->|    INVITE F5   | 
     |             100  F6             |--------------->| 
     |<--------------------------------|      180 F7    | 
     |             180 F8              |<---------------| 
     |<--------------------------------|                | 
     |                                 |     200 F9     | 
     |             200 F10             |<---------------| 
     |<--------------------------------|                | 
     |             ACK F11             |                | 
     |-------------------------------->|     ACK F12    | 
     |                                 |--------------->| 
     |                Both Way RTP Media                | 
     |<================================================>| 
     |                                 |     BYE F13    | 
     |             BYE F14             |<---------------| 
     |<--------------------------------|                | 
     |             200 F15             |                | 
     |-------------------------------->|     200 F16    | 
     |                                 |--------------->| 
     |                                 |                | 
    
   In this scenario, Alice places a call to Bob using first a 
   Redirect server then a Proxy Server.  The INVITE message is first 
   sent to the Redirect Server.  The Server returns a 302 Moved 
   Temporarily response (F2) containing a Contact header with Bob's 
   current SIP address.  Alice then generates a new INVITE and sends to 
   Bob via the Proxy Server and the call proceeds normally.  In this 
   example, no SDP is present in the INVITE, so the SDP is carried in 
   the ACK message. 
    
   The call is terminated when Bob sends a BYE message. 
    
    
   Message Details 
    
    
   F1 INVITE Alice -> Redirect Server 
 
 
Johnston et al          Expires  October 2003               [Page 57] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Length: 0 
    
    
   F2 302 Moved Temporarily Redirect Proxy -> Alice 
    
   SIP/2.0 302 Moved Temporarily 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@chicago.example.com;transport=tcp> 
   Content-Length: 0 
    
    
   F3 ACK Alice -> Redirect Server 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F4 INVITE Alice -> Proxy 3 
    
   INVITE sip:bob@chicago.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Content-Length: 0 
    
 
 
Johnston et al          Expires  October 2003               [Page 58] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
   F5 INVITE Proxy 3 -> Bob 
    
   INVITE sip:bob@client.chicago.example.com SIP/2.0 
   Via: SIP/2.0/TCP 
   ss3.chicago.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss3.chicago.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Content-Length: 0 
    
    
   F6 100 Trying Proxy 3 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Content-Length: 0 
    
    
   F7 180 Ringing Bob -> Proxy 3 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/TCP 
   ss3.chicago.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.233 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss3.chicago.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.chicago.example.com;transport=tcp> 
   Content-Length: 0 
    
    
   F8 180 Ringing Proxy 3 -> Alice 
    
 
 
Johnston et al          Expires  October 2003               [Page 59] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss3.chicago.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.chicago.example.com;transport=tcp> 
   Content-Length: 0 
    
    
   F9 200 OK Bob -> Proxy 3 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP 
   ss3.chicago.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.233 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss3.chicago.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.chicago.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 148 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.chicago.example.com 
   s=- 
   c=IN IP4 192.0.2.100 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F10 200 OK Proxy -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss3.chicago.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 INVITE 
   Contact: <sip:bob@client.chicago.example.com;transport=tcp> 
 
 
Johnston et al          Expires  October 2003               [Page 60] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Type: application/sdp 
   Content-Length: 148 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.chicago.example.com 
   s=- 
   c=IN IP4 192.0.2.100 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /* ACK contains SDP of Alice since none present in INVITE */ 
    
   F11 ACK Alice -> Proxy 3 
    
   ACK sip:bob@client.chicago.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bq9 
   Max-Forwards: 70 
   Route: <sip:ss3.chicago.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 ACK 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F12 ACK Proxy 3 -> Bob 
    
   ACK sip:bob@client.chicago.example.com SIP/2.0 
   Via: SIP/2.0/TCP 
   ss3.chicago.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bq9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 ACK 
   Content-Type: application/sdp 
 
 
Johnston et al          Expires  October 2003               [Page 61] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
   /* RTP streams are established between Alice and Bob */ 
    
   /* Bob Hangs Up with Alice. */ 
    
   F13 BYE Bob -> Proxy 3 
    
   BYE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.chicago.example.com:5060;branch=z9hG4bKfgaw2 
   Max-Forwards: 70 
   Route: <sip:ss3.chicago.example.com;lr> 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F14 BYE Proxy 3 -> Alice 
    
   BYE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/TCP 
   ss3.chicago.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.100 
   Via: SIP/2.0/TCP client.chicago.example.com:5060;branch=z9hG4bKfgaw2 
   Max-Forwards: 69 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F15 200 OK Alice -> Proxy 3 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP 
   ss3.chicago.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.233 
   Via: SIP/2.0/TCP client.chicago.example.com:5060;branch=z9hG4bKfgaw2 
 
 
Johnston et al          Expires  October 2003               [Page 62] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    ;received=192.0.2.100 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    
    
   F16 200 OK Proxy 3 -> Bob 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/TCP client.chicago.example.com:5060;branch=z9hG4bKfgaw2 
    ;received=192.0.2.100 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 BYE 
   Content-Length: 0 
    






























 
 
Johnston et al          Expires  October 2003               [Page 63] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
     
  3.7 Session with re-INVITE (IP Address Change) 
    
    
        Alice                Proxy 2                Bob 
           |   F1 INVITE        |                    | 
           |------------------->|      F2 INVITE     | 
           |   F3 100 Trying    |------------------->| 
           |<-------------------|   F4 180 Ringing   | 
           |   F5 180 Ringing   |<-------------------| 
           |<-------------------|                    | 
           |                    |    F6 200 OK       | 
           |    F7 200 OK       |<-------------------| 
           |<-------------------|                    | 
           |                 F8  ACK                 | 
           |---------------------------------------->| 
           |      Both Way RTP Media Established     | 
           |<=======================================>| 
           |                                         | 
           |           Bob changes IP address        | 
           |                                         | 
           |                 F9 INVITE               | 
           |<----------------------------------------| 
           |                F10 200 OK               | 
           |---------------------------------------->|   
           |                 F11  ACK                | 
           |<----------------------------------------| 
           |         New RTP Media Stream            | 
           |<=======================================>| 
           |                 F12 BYE                 | 
           |---------------------------------------->| 
           |               F25 200 OK                | 
           |<----------------------------------------| 
           |                                         | 
    
    
   This example shows a session in which the media is changes midway 
   through the session.  When Bobs IP address changes during the 
   session, Bob sends a re-INVITE containing a new Contact and SDP 
   (version number incremented) information to A.  In this flow, the 
   proxy does not Record-Route so is not in the SIP messaging path after 
   the initial exchange. 
    
    
   Message Details 
    
   F1 INVITE Alice -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
 
 
Johnston et al          Expires  October 2003               [Page 64] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F2 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F3 100 Trying Proxy 2 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
 
 
Johnston et al          Expires  October 2003               [Page 65] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F4 180 Ringing Bob -> Proxy 2 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F5 180 Ringing Proxy 2 -> Alice 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F6 200 OK Bob -> Proxy 2 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
 
 
Johnston et al          Expires  October 2003               [Page 66] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F7 200 OK Proxy 2 -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Type: application/sdp 
   Content-Length: 147 
    
   v=0 
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com 
   s=- 
   c=IN IP4 192.0.2.201 
   t=0 0 
   m=audio 3456 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
      
    
   F8 ACK Alice -> Bob 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b7b 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   /* RTP streams are established between Alice and Bob */ 
    
   /* Bob changes IP address and re-INVITEs Alice with new Contact and 
   SDP */ 
    
   F9 INVITE Bob -> Alice 
 
 
Johnston et al          Expires  October 2003               [Page 67] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
   INVITE sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.chicago.example.com:5060;branch=z9hG4bKlkld5l 
   Max-Forwards: 70 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 14 INVITE 
   Contact: <sip:bob@client.chicago.example.com> 
   Content-Type: application/sdp 
   Content-Length: 149 
    
   v=0 
   o=bob 2890844527 2890844528 IN IP4 client.chicago.example.com 
   s=- 
   c=IN IP4 192.0.2.100 
   t=0 0 
   m=audio 47172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F10 200 OK Alice ->B 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.chicago.example.com:5060;branch=z9hG4bKlkld5l 
    ;received=192.0.2.100 
   Max-Forwards: 70 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 14 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 150 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 1000 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F11 ACK Bob -> Alice 
    
   ACK sip:alice@client.atlanta.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.chicago.example.com:5060;branch=z9hG4bKlkldcc 
   Max-Forwards: 70 
 
 
Johnston et al          Expires  October 2003               [Page 68] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   From: Bob <sip:bob@biloxi.example.com>;tag=314159 
   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 14 ACK 
   Content-Length: 0 
    
    
   /* New RTP stream established between Alice and Bob */ 
    
   /* Alice hangs up with Bob */ 
    
   F12 BYE Alice -> Bob 
    
   BYE sip:bob@client.chicago.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bo4 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 BYE 
   Content-Length: 0 
    
    
   F13 200 OK Bob -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bo4 
    ;received=192.0.2.101 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 2 BYE 
   Content-Length: 0 
    
    
    












 
 
Johnston et al          Expires  October 2003               [Page 69] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
 3.8 Unsuccessful No Answer 
    
   Alice           Proxy 1          Proxy 2            Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|   INVITE F2    |                | 
     |     100  F3    |--------------->|   INVITE F4    | 
     |<---------------|     100  F5    |--------------->| 
     |                |<---------------|                | 
     |                |                |      180 F6    | 
     |                |     180 F7     |<---------------| 
     |     180 F8     |<---------------|                | 
     |<---------------|                |                | 
     |                |                |                | 
     |   CANCEL F9    |                |                | 
     |--------------->|                |                | 
     |     200 F10    |                |                | 
     |<---------------|   CANCEL F11   |                | 
     |                |--------------->|                | 
     |                |     200 F12    |                | 
     |                |<---------------|                | 
     |                |                |   CANCEL F13   | 
     |                |                |--------------->| 
     |                |                |     200 F14    | 
     |                |                |<---------------| 
     |                |                |     487 F15    | 
     |                |                |<---------------| 
     |                |                |     ACK F16    | 
     |                |     487 F17    |--------------->| 
     |                |<---------------|                | 
     |                |     ACK F18    |                | 
     |     487 F19    |--------------->|                | 
     |<---------------|                |                | 
     |     ACK F20    |                |                | 
     |--------------->|                |                | 
     |                |                |                | 
    
   In this scenario, Alice gives up on the call before Bob answers 
   (sends a 200 OK response).  Alice sends a CANCEL (F9) since no final 
   response had been received from Bob.  If a 200 OK to the INVITE 
   had crossed with the CANCEL, Alice would have sent an ACK then a BYE 
   to Bob in order to properly terminate the call. 
    
   Note that the CANCEL message is acknowledged with a 200 OK on a hop 
   by hop basis, rather than end to end. 
    
    
    
    
 
 
Johnston et al          Expires  October 2003               [Page 70] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
   Message Details 
    
    
   F1 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Proxy-Authorization: Digest username="alice",  
    realm="atlanta.example.com", 
    nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="b00b416324679d7e243f55708d44be7b" 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /*Client for Alice prepares to receive data on port 49172 from the 
   network.*/ 
    
   F2 INVITE Proxy 1 -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
 
 
Johnston et al          Expires  October 2003               [Page 71] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F3 100 Trying Proxy 1 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F4 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.client.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   Max-Forwards: 68 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
 
 
Johnston et al          Expires  October 2003               [Page 72] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   a=rtpmap:0 PCMU/8000 
    
    
   F5 100 Trying Proxy 2 -> Proxy 1 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F6 180 Ringing Bob -> Proxy 2 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP 
   ss2.client.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F7 180 Ringing Proxy 2 -> Proxy 1 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
 
 
Johnston et al          Expires  October 2003               [Page 73] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F8 180 Ringing Proxy 1 -> Alice 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F9 CANCEL Alice -> Proxy 1 
    
   CANCEL sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Route: <sip:ss1.atlanta.example.com;lr> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 CANCEL 
   Content-Length: 0 
    
    
   F10 200 OK Proxy 1 -> Alice 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 CANCEL 
   Content-Length: 0 
    
    
   F11 CANCEL Proxy 1 -> Proxy 2 
    
   CANCEL sip:alice@atlanta.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
 
 
Johnston et al          Expires  October 2003               [Page 74] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 CANCEL 
   Content-Length: 0 
    
    
   F12 200 OK Proxy 2 -> Proxy 1 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 CANCEL 
   Content-Length: 0 
    
    
   F13 CANCEL Proxy 2 -> Bob 
    
   CANCEL sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 CANCEL 
   Content-Length: 0 
    
    
   F14 200 OK Bob -> Proxy 2 
    
   SIP/2.0 200 OK 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 CANCEL 
   Content-Length: 0 
    
    
   F15 487 Request Terminated Bob -> Proxy 2 
    
   SIP/2.0 487 Request Terminated 
 
 
Johnston et al          Expires  October 2003               [Page 75] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F16 ACK Proxy 2 -> Bob 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F17 487 Request Terminated Proxy 2 -> Proxy 1 
    
   SIP/2.0 487 Request Terminated 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F18 ACK Proxy 1 -> Proxy 2 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
 
 
Johnston et al          Expires  October 2003               [Page 76] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F19 487 Request Terminated Proxy 1 -> Alice 
    
   SIP/2.0 487 Request Terminated 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
    
    
   F20 ACK Alice -> Proxy 1 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   Proxy-Authorization: Digest username="alice",  
    realm="atlanta.example.com", 
    nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="b00b416324679d7e243f55708d44be7b" 
   CSeq: 1 ACK 
   Content-Length: 0 
    
     
















 
 
Johnston et al          Expires  October 2003               [Page 77] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
 3.9 Unsuccessful Busy  
    
   Alice           Proxy 1          Proxy 2            Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|   INVITE F2    |                | 
     |     100  F3    |--------------->|   INVITE F4    | 
     |<---------------|     100  F5    |--------------->| 
     |                |<---------------|                | 
     |                |                |      486 F6    | 
     |                |                |<---------------| 
     |                |                |     ACK F7     | 
     |                |      486 F8    |--------------->| 
     |                |<---------------|                | 
     |                |      ACK F9    |                | 
     |     486 F10    |--------------->|                | 
     |<---------------|                |                | 
     |     ACK F11    |                |                | 
     |--------------->|                |                | 
     |                |                |                | 
    
    
   In this scenario, Bob is busy and sends a 486 Busy Here response 
   to Alice's INVITE.  Note that the non-2xx response is acknowledged on 
   a hop-by-hop basis instead of end-to-end.  Also note that many SIP 
   UAs will not return a 486 response, as they have multiple line and 
   other features. 
    
    
   Message Details 
    
    
   F1 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Proxy-Authorization: Digest username="alice",  
    realm="atlanta.example.com", 
    nonce="dc3a5ab2530aa93112cf5904ba7d88fa", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="702138b27d869ac8741e10ec643d55be" 
   Content-Type: application/sdp 
 
 
Johnston et al          Expires  October 2003               [Page 78] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /*Client for Alice prepares to receive data on port 49172 from the 
   network.*/ 
    
   F2 INVITE Proxy 1 -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F3 100 Trying Proxy 1 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
 
 
Johnston et al          Expires  October 2003               [Page 79] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    
    
   F4 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 68 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F5 100 Trying Proxy 2 -> Proxy 1 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F6 486 Busy Here Bob -> Proxy 2 
    
   SIP/2.0  486 Busy Here 

 
 
Johnston et al          Expires  October 2003               [Page 80] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F7 ACK Proxy 2 -> Bob 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F8 486 Busy Here Proxy 2 -> Proxy 1 
    
   SIP/2.0  486 Busy Here 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F9 ACK Proxy 1 -> Proxy 2 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
 
 
Johnston et al          Expires  October 2003               [Page 81] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F10 486 Busy Here Proxy 1 -> Alice 
    
   SIP/2.0  486 Busy Here 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F11 ACK Alice -> Proxy 1 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Proxy-Authorization: Digest username="alice",  
    realm="atlanta.example.com", 
    nonce="dc3a5ab2530aa93112cf5904ba7d88fa", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="702138b27d869ac8741e10ec643d55be" 
   Content-Length: 0 
    
    
    
    
    
    
    
     










 
 
Johnston et al          Expires  October 2003               [Page 82] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
 3.10 Unsuccessful No Response from User Agent 
    
   Alice           Proxy 1          Proxy 2            Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|   INVITE F2    |                | 
     |     100  F3    |--------------->|   INVITE F4    | 
     |<---------------|     100  F5    |--------------->| 
     |                |<---------------|   INVITE F6    | 
     |                |                |--------------->| 
     |                |                |   INVITE F7    | 
     |                |                |--------------->| 
     |                |                |   INVITE F8    | 
     |                |                |--------------->| 
     |                |                |   INVITE F9    | 
     |                |                |--------------->| 
     |                |                |   INVITE F10   | 
     |                |                |--------------->| 
     |                |                |   INVITE F11   | 
     |                |     480 F12    |--------------->| 
     |                |<---------------|                | 
     |                |     ACK F13    |                | 
     |     480 F14    |--------------->|                | 
     |<---------------|                |                | 
     |     ACK F15    |                |                | 
     |--------------->|                |                | 
     |                |                |                | 
    
   In this example, there is no response from Bob to Alice's INVITE 
   messages being re-transmitted by Proxy 2.  After the sixth re- 
   transmission, Proxy 2 gives up and sends a 480 No Response to Alice.   
    
    
   Message Details 
    
    
   F1 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Proxy-Authorization: Digest username="alice",  
    realm="atlanta.example.com", 
 
 
Johnston et al          Expires  October 2003               [Page 83] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
    nonce="cf5904ba7d8dc3a5ab2530aa931128fa", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="7afc04be7961f053c24f80e7dbaf888f" 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /*Client for Alice prepares to receive data on port 49172 from the 
   network.*/ 
    
   F2 INVITE Proxy 1 -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F3 100 Trying Proxy 1 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
 
 
Johnston et al          Expires  October 2003               [Page 84] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F4 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 68 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F5 100 Trying Proxy 2 -> Proxy 1 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
 
 
Johnston et al          Expires  October 2003               [Page 85] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   F6 INVITE Proxy 2 -> Bob 
    
   Resend of Message F4 
    
    
   F7 INVITE Proxy 2 -> Bob 
    
   Resend of Message F4 
    
    
   F8 INVITE Proxy 2 -> Bob 
    
   Resend of Message F4 
    
    
   F9 INVITE Proxy 2 -> Bob 
    
   Resend of Message F4 
    
    
   F10 INVITE Proxy 2 -> Bob 
    
   Resend of Message F4 
    
    
   F11 INVITE Proxy 2 -> Bob 
    
   Resend of Message F4 
    
    
   /* Proxy 2 gives up */ 
    
   F12 480 No Response Proxy 2 -> Proxy 1 
    
   SIP/2.0 480 No Response 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F13 ACK Proxy 1 -> Proxy 2 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
 
 
Johnston et al          Expires  October 2003               [Page 86] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F14 480 No Response Proxy 1 -> Alice 
    
   SIP/2.0 480 No Response 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F15 ACK Alice -> Proxy 1 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Proxy-Authorization: Digest username="alice",  
    realm="atlanta.example.com", 
    nonce="cf5904ba7d8dc3a5ab2530aa931128fa", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="7afc04be7961f053c24f80e7dbaf888f" 
   Content-Length: 0 
    
    
    
     









 
 
Johnston et al          Expires  October 2003               [Page 87] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
 3.11 Unsuccessful Temporarily Unavailable 
    
   Alice          Proxy 1          Proxy 2            Bob 
     |                |                |                | 
     |   INVITE F1    |                |                | 
     |--------------->|   INVITE F2    |                | 
     |     100  F3    |--------------->|   INVITE F4    | 
     |<---------------|     100  F5    |--------------->| 
     |                |<---------------|      180 F6    | 
     |                |     180 F7     |<---------------| 
     |     180 F8     |<---------------|                | 
     |<---------------|                |     480 F9     | 
     |                |                |<---------------| 
     |                |                |     ACK F10    | 
     |                |     480 F11    |--------------->| 
     |                |<---------------|                | 
     |                |     ACK F12    |                | 
     |     480 F13    |--------------->|                | 
     |<---------------|                |                | 
     |     ACK F14    |                |                | 
     |--------------->|                |                | 
     |                |                |                | 
    
    
   In this scenario, Bob initially sends a 180 Ringing response to 
   Alice, indicating that alerting is taking place.  However, then a 
   480 Unavailable is then sent to Alice.  This response is 
   acknowledged then proxied back to Alice. 
    
    
   Message Details 
    
    
   F1 INVITE Alice -> Proxy 1 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Proxy-Authorization: Digest username="alice",  
    realm="atlanta.example.com", 
    nonce="aa9311cf5904ba7d8dc3a5ab253028fa", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="59a46a91bf1646562a4d486c84b399db" 
 
 
Johnston et al          Expires  October 2003               [Page 88] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   /*Client for Alice prepares to receive data on port 49172 from the 
   network.*/ 
    
   F2 INVITE Proxy 1 -> Proxy 2 
    
   INVITE sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 69 
   Record-Route: <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F3 100 Trying Proxy 1 -> Alice 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
 
 
Johnston et al          Expires  October 2003               [Page 89] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Content-Length: 0 
    
    
   F4 INVITE Proxy 2 -> Bob 
    
   INVITE sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Max-Forwards: 68 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:alice@client.atlanta.example.com> 
   Content-Type: application/sdp 
   Content-Length: 151 
    
   v=0 
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com 
   s=- 
   c=IN IP4 192.0.2.101 
   t=0 0 
   m=audio 49172 RTP/AVP 0 
   a=rtpmap:0 PCMU/8000 
    
    
   F5 100 Trying Proxy 2 -> Proxy 1 
    
   SIP/2.0 100 Trying 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com> 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F6 180 Ringing Bob -> Proxy 2 
    
   SIP/2.0 180 Ringing 
 
 
Johnston et al          Expires  October 2003               [Page 90] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F7 180 Ringing Proxy 2 -> Proxy 1 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
   F8 180 Ringing Proxy 1 -> Alice 
    
   SIP/2.0 180 Ringing 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   Record-Route: <sip:ss2.biloxi.example.com;lr>, 
   <sip:ss1.atlanta.example.com;lr> 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Contact: <sip:bob@client.biloxi.example.com> 
   Content-Length: 0 
    
    
 
 
Johnston et al          Expires  October 2003               [Page 91] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   F9 480 Temporarily Unavailable Bob -> Proxy 2 
    
   SIP/2.0 480 Temporarily Unavailable 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
    ;received=192.0.2.222 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F10 ACK Proxy 2 -> Bob 
    
   ACK sip:bob@client.biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP 
   ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F11 480 Temporarily Unavailable Proxy 2 -> Proxy 1 
    
   SIP/2.0 480 Temporarily Unavailable 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
    ;received=192.0.2.111 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F12 ACK Proxy 1 -> Proxy 2 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 
   Max-Forwards: 70 
 
 
Johnston et al          Expires  October 2003               [Page 92] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 ACK 
   Content-Length: 0 
    
    
   F13 480 Temporarily Unavailable Proxy 1 -> Alice 
    
   SIP/2.0 480 Temporarily Unavailable 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
    ;received=192.0.2.101 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   CSeq: 1 INVITE 
   Content-Length: 0 
    
    
   F14 ACK Alice -> Proxy 1 
    
   ACK sip:bob@biloxi.example.com SIP/2.0 
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 
   Max-Forwards: 70 
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl 
   To: Bob <sip:bob@biloxi.example.com>;tag=314159 
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com 
   Proxy-Authorization: Digest username="alice",  
    realm="atlanta.example.com", 
    nonce="aa9311cf5904ba7d8dc3a5ab253028fa", opaque="", 
    uri="sip:bob@biloxi.example.com", 
    response="59a46a91bf1646562a4d486c84b399db" 
   CSeq: 1 ACK 
   Content-Length: 0 
    
Security Considerations 
    
   Since this document contains examples of SIP session establishment, 
   the security considerations in RFC 3261 [1] apply.  RFC 3261 
   describes the basic threats including registration hijacking, server 
   impersonation, message body tampering, session modifying or teardown, 
   and denial of service and amplification attacks.  The use of HTTP 
   Digest as shown in this document provides one-way authentication and 
   protection against replay attacks.  TLS transport is used in 
   registration scenarios due to the lack of integrity protection in 
   HTTP Digest and the danger of registration hijacking without it, as 
   described in RFC 3261 [1].  A full discussion of the weaknesses of 
   HTTP Digest is provided in RFC 3261 [1].  The use of TLS and the 
   Secure SIP (sips) URI scheme provides a better level of security 
 
 
Johnston et al          Expires  October 2003               [Page 93] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   including two-way authentication. S/MIME can provide end-to-end 
   confidentiality and integrity protection of message bodies, as 
   described in RFC 3261. 
    
Normative References 
    
                     
  1 Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 
      Peterson, J., Sparks, R., Handley, M., and Schooler, E., "SIP: 
      Session Initiation Protocol", RFC 3261, June 2002. 
   
  2 Rosenberg, J. and Schulzrinne, H., "An Offer/Answer Model with 
      SDP", Internet Engineering Task Force, RFC 3264, April 2002. 
   
  3 Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, 
      P., Luotonen, A. and Stewart, L., "HTTP authentication: Basic and 
      Digest Access Authentication", RFC 2617, June 1999. 
    
    
    
Informative References 
     
    
  4 Johnston, A., Donovan, S., Sparks, R., Cunningham, C., Summers, K., 
      "Session Initiation Protocol PSTN Call Flow Examples", RFC xxxx, 
      August 2002. 
    
    
Acknowledgments 
    
   This document is has been a group effort by the SIP and SIPPING WGs.  
   The authors wish to thank everyone who has read, reviewed, commented, 
   or made suggestions to improve this document. 
    
   Thanks to Rohan Mahy, Adam Roach, Gonzalo Camarillo, Cullen Jennings, 
   and Tom Taylor for their detailed comments during the final review.  
   Thanks to Dean Willis for his early contributions to the development 
   of this document. 
    
   The authors wish to thank Neil Deason for his additions to the 
   Torture Test messages and Kundan Singh for performing parser 
   validation of messages.  
    
   The authors wish to thank the following individuals for their 
   participation in the review of this call flows document: Aseem 
   Agarwal, Rafi Assadi, Ben Campbell, Sunitha Kumar, Jon Peterson, Marc 
   Petit-Huguenin, Vidhi Rastogi, and Bodgey Yin Shaohua.   
    

 
 
Johnston et al          Expires  October 2003               [Page 94] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   The authors also wish to thank the following individuals for their 
   assistance: Jean-Francois Mule, Hemant Agrawal, Henry Sinnreich, 
   David Devanatham, Joe Pizzimenti, Matt Cannon, John Hearty, the whole 
   MCI WorldCom IPOP Design team, Scott Orton, Greg Osterhout, Pat 
   Sollee, Doug Weisenberg, Danny Mistry, Steve McKinnon, and Denise 
   Ingram, Denise Caballero, Tom Redman, Ilya Slain, Pat Sollee, John 
   Truetken, and others from MCI WorldCom, 3Com, Cisco, Lucent and 
   Nortel. 
    
Author's Addresses 
    
   All listed authors actively contributed large amounts of text to this 
   document. 
    
      Alan Johnston 
      WorldCom 
      100 South 4th Street 
      St. Louis, MO 63102 
      USA 
    
      EMail:  alan.johnston@wcom.com 
    
    
      Steve Donovan 
      dynamicsoft, Inc. 
      5100 Tennyson Parkway 
      Suite 1200 
      Plano, Texas 75024 
      USA 
    
      EMail:  sdonovan@dynamicsoft.com 
    
    
      Robert Sparks 
      dynamicsoft, Inc. 
      5100 Tennyson Parkway 
      Suite 1200 
      Plano, Texas 75024 
      USA 
    
      EMail:  rsparks@dynamicsoft.com 
    
      Chris Cunningham 
      dynamicsoft, Inc. 
      5100 Tennyson Parkway 
      Suite 1200 
      Plano, Texas 75024 
      USA 
    
 
 
Johnston et al          Expires  October 2003               [Page 95] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
      EMail: ccunningham@dynamicsoft.com 
    
       
      Kevin Summers 
      Sonus 
      1701 North Collins Blvd, Suite 3000 
      Richardson, TX 75080 
      USA 
    
      Email: kevin.summers@sonusnet.com 
    
    
Intellectual Property Statement 
    
   The IETF takes no position regarding the validity or scope of any 
   intellectual property or other rights that might be claimed to 
   pertain to the implementation or use of the technology described in 
   this document or the extent to which any license under such rights 
   might or might not be available; neither does it represent that it 
   has made any effort to identify any such rights. Information on the 
   IETF's procedures with respect to rights in standards-track and 
   standards-related documentation can be found in BCP-11. Copies of 
   claims of rights made available for publication and any assurances of 
   licenses to be made available, or the result of an attempt made to 
   obtain a general license or permission for the use of such 
   proprietary rights by implementors or users of this specification can 
   be obtained from the IETF Secretariat. 
    
   The IETF invites any interested party to bring to its attention any 
   copyrights, patents or patent applications, or other proprietary 
   rights which may cover technology that may be required to practice 
   this standard. Please address the information to the IETF Executive 
   Director. 
    
    
Full Copyright Statement 
    
   Copyright (C) The Internet Society (2003). All Rights Reserved. 
    
   This document and translations of it may be copied and furnished to 
   others, and derivative works that comment on or otherwise explain it 
   or assist in its implementation may be prepared, copied, published 
   and distributed, in whole or in part, without restriction of any 
   kind, provided that the above copyright notice and this paragraph are 
   included on all such copies and derivative works. However, this 
   document itself may not be modified in any way, such as by removing 
   the copyright notice or references to the Internet Society or other 
   Internet organizations, except as needed for the purpose of 
   developing Internet standards in which case the procedures for 
 
 
Johnston et al          Expires  October 2003               [Page 96] 

                     SIP Basic Call Flow Examples           April 2003 
 
 
   copyrights defined in the Internet Standards process must be 
   followed, or as required to translate it into languages other than 
   English. 
    
   The limited permissions granted above are perpetual and will not be 
   revoked by the Internet Society or its successors or assignees. 
    
   This document and the information contained herein is provided on an 
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 
    
 
Acknowledgement 
 
   Funding for the RFC Editor function is currently provided by the 
   Internet Society. 
    




























 
 
Johnston et al          Expires  October 2003               [Page 97]