Internet Engineering Task Force Steven R. Donovan INTERNET DRAFT MCI February 8, 1999 Expires August 8, 1999 The SIP INFO Method Status of this document This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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." To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Abstract This document proposes an extension to the Session Initiation Protocol. This extension adds the INFO method to the SIP protocol. The intent of the INFO method is to allow for the carrying of session related control information that is generated during a session. Examples of such session control information are ISUP/ISDN signaling messages and DTMF digits used to control telephony services. Donovan [Page 1] Internet draft The SIP INFO Method February 8, 1999 1.0 Introduction There are situations where session related control information needs to be sent during a session. This information is separate from the media that is being exchanged as part of the session. Two examples of this are motivated by telephony related services: 1 - Mid Call Telephony Signaling Messages 2 - DTMF Digit/Dial Plus Control of Telephony Services It can also be envisioned that there will be non telephony inspired uses of a mechanism for relaying mid session information between participants of the session and to Proxy Servers interested in the session. This document proposes the addition of the INFO Request method to the SIP specification. 1.1 Mid Call Telephony Signaling Messages The first use for the INFO method is the need to carry mid call signaling information resulting from the interworking between an ISUP or ISDN network/device and a SIP controlled network. One specific example of this interworking is when the SIP controlled network is used for transport between two PSTN locations. For this call, there will be a PSTN leg from the calling party to the SIP network, a SIP leg through the SIP network and a PSTN leg from the SIP network to the called party. There needs to be a method to carry mid- call PSTN signaling that is originated by the calling party through the SIP network to the called party. 1.2 DTMF Digit/Dial Plus Control of Telephony Services The second type of telephony session control information that needs to be carried during a session is DTMF or dial plus (refered to from here on as DTMF) generated information. There are various telephony services implemented today which require the use of DTMF digits. Due to the design of these features, the DTMF information needs to be carried both as part of the media stream (in the RTP flow) and as part of the signaling or control path. This is due to the fact that there is an implicit separation of the media and control path in the SIP protocol. Thus, SIP Proxy Servers that implement services that require DTMF control and that are not in the media path require a mechanism to be notified of the DTMF digits. Donovan [Page 2] Internet draft The SIP INFO Method February 8, 1999 2.0 INFO Method The INFO method is used for communicating mid-session control information along the signaling path for the session. The signaling path for the INFO method is the signaling path established as a result of the session setup. The mid-session control information can be communicated in either an INFO message header or as part of an attachment. If the control information is telephony signaling information than the signaling message would be carried as part of an ISUP attachment to the INFO message as described in draft-ietf-sigtran-mime-isup-00.txt. The method for carrying the DTMF information in the INFO message has not yet been defined and is outside the scope of this document. 2.1 Header Field Support for INFO Method The following table is an extension of tables 4 and 5 in the SIP specification. Refer to the SIP Specification for a description of the content of the table. Header Where INFO ------ ----- ---- Accept R - Accept-Encoding R - Accept-Language R o Allow 200 - Allow 405 o Authorization R o Call-ID gc m Contact R - Contact 1xx - Contact 2xx - Contact 3xx - Contact 485 - Content-Encoding e o Content-Length e o Content-Type e * CSeq gc m Date g o Encryption g o Expires g - >From gc m Hide R o Max-Forwards R o Organization g o Donovan [Page 3] Internet draft The SIP INFO Method February 8, 1999 Header Where INFO ------ ----- ---- Priority R o Proxy-Authenticate 407 o Proxy-Authorization R o Proxy-Require R o Require R o Retry-After R - Retry-After 404,480,486 o Retry-After 503 o Retry-After 600,603 o Response-Key R o Record-Route R o Record-Route 2xx o Route R o Server r o Subject R - Timestamp g o To gc(1) m Unsupported 420 o User-Agent g o Via gc(2) m Warning r o WWW-Authenticate 401 o 2.2 Responses to the INFO Request Method A 200 OK response shall be sent if the INFO request was successful. Request Failure (4xx), Server Failure (5xx) and Global Failure (6xx) responses can also be sent for the INFO Request. 2.3 Message Body Inclusion The INFO request may contain a message body. 2.4 Behavior of SIP User Agents The protocol rules applied by the SIP User Agent shall be similar to those applied used for the BYE request. However, the INFO message shall shall not change the state of the session. 2.5 Behavior of SIP Proxy and Redirect Servers 2.5.1 Proxy Server The protocol rules applied by the SIP Proxy Server shall be similar to those applied used for the BYE request. However, the INFO message shall shall not change the state of the session. Donovan [Page 4] Internet draft The SIP INFO Method February 8, 1999 2.5.2 Forking Proxy Server The protocol rules applied by the SIP Forking Proxy Server shall be similar to those applied used for the BYE request. However, the INFO message shall shall not change the state of the session. 2.5.3 Redirection Server A redirection server should not receive the INFO method as it is a part of the signaling path only at the initiation of the session. As such, a redirection server should send a 403 Forbidden response. 2.6 Security Considerations There are no security issues specific to the INFO method. The security requirements specified in the SIP specification apply to the INFO method. 3.0 References [1] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: Session Initiation Protocol", Internet Draft, Internet Engineering Task Force, January 15, 1999. Work in progress. [2] C. Huitema, "The multipart/sip-id media type", Internet Draft, Internet Engineering Task Force, February 5, 1999. Work in Progress 4.0 Author's Address Steve Donovan MCI Worldcom 1493/678 901 International Parkway Richardson, Texas 75081 Email: steven.r.donovan@mci.com Donovan [Page 5]