Internet DRAFT - draft-ietf-ecrit-unauthenticated-access
draft-ietf-ecrit-unauthenticated-access
ECRIT H. Schulzrinne
Internet-Draft Columbia University
Intended status: Standards Track S. McCann
Expires: February 13, 2015 Research in Motion UK Ltd
G. Bajko
H. Tschofenig
D. Kroeselberg
Siemens
August 12, 2014
Extensions to the Emergency Services Architecture for dealing with
Unauthenticated and Unauthorized Devices
draft-ietf-ecrit-unauthenticated-access-10.txt
Abstract
This document provides a problem statement, introduces terminology
and describes an extension for the base IETF emergency services
architecture to address cases where an emergency caller is not
authenticated, has no identifiable service provider, or has no
remaining credit with which to pay for access to the network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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."
This Internet-Draft will expire on February 13, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Use Case Categories . . . . . . . . . . . . . . . . . . . . . 5
4. ZBP Considerations . . . . . . . . . . . . . . . . . . . . . 11
5. NASP Considerations . . . . . . . . . . . . . . . . . . . . . 11
5.1. End Host Profile . . . . . . . . . . . . . . . . . . . . 14
5.1.1. LoST Server Discovery . . . . . . . . . . . . . . . . 14
5.1.2. ESRP Discovery . . . . . . . . . . . . . . . . . . . 14
5.1.3. Location Determination and Location Configuration . . 14
5.1.4. Emergency Call Identification . . . . . . . . . . . . 14
5.1.5. SIP Emergency Call Signaling . . . . . . . . . . . . 14
5.1.6. Media . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1.7. Testing . . . . . . . . . . . . . . . . . . . . . . . 15
5.2. IAP/ISP Profile . . . . . . . . . . . . . . . . . . . . . 15
5.2.1. ESRP Discovery . . . . . . . . . . . . . . . . . . . 15
5.2.2. Location Determination and Location Configuration . . 15
5.3. ESRP Profile . . . . . . . . . . . . . . . . . . . . . . 15
5.3.1. Emergency Call Routing . . . . . . . . . . . . . . . 15
5.3.2. Emergency Call Identification . . . . . . . . . . . . 15
5.3.3. SIP Emergency Call Signaling . . . . . . . . . . . . 16
6. Lower Layer Considerations for NAA Case . . . . . . . . . . . 16
6.1. Link Layer Emergency Indication . . . . . . . . . . . . . 17
6.2. Securing Network Attachment in NAA Cases . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
10.1. Normative References . . . . . . . . . . . . . . . . . . 21
10.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
Summoning police, the fire department or an ambulance in emergencies
is one of the fundamental and most-valued functions of the telephone.
As telephone functionality moves from circuit-switched telephony to
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Internet telephony, its users rightfully expect that this core
functionality will continue to work at least as well as it has for
the older technology. New devices and services are being made
available that could be used to make a request for help, those
devices are not traditional telephones, and users are increasingly
expecting them to be used to place emergency calls.
Roughly speaking, the IETF emergency services architecture (see
[RFC6881] and [RFC6443]) divides responsibility for handling
emergency calls among the access network (ISP); the application
service provider (ASP), which may be a VoIP service provider (VSP);
and the provider of emergency signaling services, the emergency
service network (ESN). The access network may provide location
information to end systems, but does not have to provide any ASP
signaling functionality. The emergency caller can reach the ESN
either directly or through the ASP's outbound proxy. Any of the
three parties can provide the mapping from location to PSAP URI by
offering LoST [RFC5222] services.
In general, a set of automated configuration mechanisms allows a
device to function in a variety of architectures, without the user
being aware of the details on who provides location, mapping services
or call routing services. However, if emergency calling is to be
supported when the calling device lacks access network authorization
or does not have an ASP, one or more of the providers may need to
provide additional services and functions.
In all cases, the end device has to be able to perform a LoST lookup
and otherwise conduct the emergency call in the same manner as when
the three exceptional conditions discussed below do not apply.
We distinguish among three conditions:
No Access Authentication (NAA): In the NAA case, the emergency
caller does not posses valid credentials for the access network.
This includes the case where the access network allows pay-per-
use, as is common for wireless hotspots, but there is insufficient
time to enter credit card details and other registration
information required for access. It also covers all cases where
either no credentials are available at all, or the available
credentials do not work for the given IAP/ISP. As a result, the
NAA case basically combines the below NASP and ZBP cases, but at
the IAP/ISP level. Support for emergency call handling in the NAA
case is subject to the local policy of the ISP. Such policy may
vary substantially between ISPs and typically depends on external
factors that are not under the ISP control.
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No ASP (NASP): The caller does not have an ASP at the time of the
call. This can occur either in case the caller does not possess
any valid subscription for a reachable ASP, or in case none of the
ASPs where the caller owns a valid subscription is reachable
through the ISP.
Note: The interoperability need is increased with this scenario
since the client software used by the emergency caller must be
compatible with the protocols and extensions deployed by the ESN.
Zero-balance ASP (ZBP): In the case of zero-balance ASP, the ASP can
authenticate the caller, but the caller is not authorized to use
ASP services, e.g., because the contract has expired or the
prepaid account for the customer has been depleted.
These three cases are not mutually exclusive. A caller in need of
help may, for example, be in a NAA and NASP situation, as explained
in more detail in Figure 1. Depending on local policy and
regulations, it may not be possible to place emergency calls in the
NAA case. Unless local regulations require user identification, it
should always be possible to place calls in the NASP case, with
minimal impact on the ISP. Unless the ESN requires that all calls
traverse a known set of VSPs, it is technically possible to let a
caller place an emergency call in the ZBP case. We discuss each case
in more details in Section 3.
As mentioned in the abstract some of the functionality provided in
this document is already available in the PSTN. Consequently, there
is real-world experience available and not all of it is positive.
For example, the functionality of SIM-less calls in today's cellular
system has lead to a fair amount of hoax or test calls in certain
countries. This causes overload situations at PSAPs, which is
considered harmful to the overall availability and reliability of
emergency services.
As an example, Federal Office of Communications (OFCOM,
Switzerland) provided statistics about emergency (112) calls in
Switzerland from Jan. 1997 to Nov. 2001. Switzerland did not
offer SIM-less emergency calls except for almost a month in July
2000 where a significant increase in hoax and test calls was
reported. As a consequence, the functionality was disabled again.
More details can be found in the panel presentations of the 3rd
SDO Emergency Services Workshop [esw07].
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2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119
[RFC2119].
This document reuses terminology from [RFC5687] and [RFC5012], namely
Internet Access Provider (IAP), Internet Service Provider (ISP),
Application Service Provider (ASP), Voice Service Provider (VSP),
Emergency Service Routing Proxy (ESRP), Public Safety Answering Point
(PSAP), Location Configuration Server (LCS), (emergency) service dial
string, and (emergency) service identifier.
3. Use Case Categories
On a very high-level, the steps to be performed by an end host that
is not attached to the network and the user starting to make an
emergency call are the following:
Link Layer Attachment: Some networks have added support for
unauthenticated emergency access, some other type of networks
advertise these capabilities using layer beacons. The end host
learns about these unauthenticated emergency services capabilities
either from the link layer type or from advertisement.
The end host uses the link layer specific network attachment
procedures defined for unauthenticated network access in order to
get access to the network.
Pre-Emergency Service Configuration: When the link layer network
attachment procedure is completed the end host learns basic
configuration information using DHCP from the ISP. The end host
uses a Location Configuration Protocol (LCP) to retrieve location
information. Subsequently, the LoST protocol [RFC5222] is used to
learn the relevant emergency numbers, and to obtain the PSAP URI
applicable for that location.
Emergency Call: In case of need for help, a user dials an emergency
number and the SIP UA initiates the emergency call procedures by
communicating with the PSAP.
Figure 1 compiles the basic logic taking place during network entry
for requesting an emergency service and shows the interrelation
between the three conditions described in the above section.
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+-----Y
|Start|
`...../
|
| Are credentials
| for network attachment
| available?
|
NO v YES
+----------------------------+
| |
| |
V v
.............. ................
| Idle: Wait | |Execute |
| for ES Call| |LLA Procedures|
| Initiation | "--------------'
"------------' |
Is | +---------->O
emergency | | | Is ASP
service | NO +-----Y | | configured?
network +--->| End | | +---------------+
attachment| `...../ | YES | | NO
possible? | | | |
v | v v
+------------+ | +------------+ +------------+
| Execute | | | Execute | | Execute |
| NAA |--------+ | Phone BCP | | NASP |
| Procedures | | Procedures | | Procedures |
+------------+ +------------+ +------------+
Authorization for| |
making an | |
emergency call | |
with the ASP/VSP?| |
+--------------+ v
| NO | YES +-----Y
| | | Done|
v v `...../
+------------+ +------------+
| Execute | | Execute |
| ZBP | | Phone BCP |
| Procedures | | Procedures |
+------------+ +------------+
| |
| |
v v
+-----Y +-----Y
| Done| | Done|
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`...../ `...../
Abbreviations:
LLA: Link Layer Attachment
ES: Emergency Services
Figure 1: Flow Diagram: NAA, ZBP, and NSAP Scenarios.
The diagrams below highlight the most important steps for the three
cases.
+-----Y
|Start|
`...../
|
| No
| credentials
| for network access
| available
v
..............
| Idle: Wait |
| for ES Call|
| Initiation |
"------------'
|
|
|
v
--
// --
/ --
// Is --
/ emergency --
| service | NO +--------+
| network |------>| Call |
| attachment | Failed |
\ possible? / `......./
\ //
\\ //
\ //
\--/
|
| YES
|
|
v
+------------+
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| Execute |
| NAA |
| Procedures |
+------------+
|
| Network
| attachment
| in progress
v
/--\ Continue
| | with
| | application
\--/ layer interaction
Figure 2: Flow Diagram: NAA Scenario.
+-----+
+------------|Start|-----------------+
| `...../ |
v v
+------------+ +----------------+
| NAA | | Regular |
| Procedures | | Network Access |
+------------+ | Procedures |
| +----------------+
| |
| |
----------------o--------------------+
|
|
|
|
Network
Attachment
Completed
|
|
|
|
v
+------------+ +---------+
| ASP | NO | See |
| Configured?|----->| main |
+------------+ | diagram |
| `......../
|
| YES
|
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v
//----
/ --
// --
/ - +---------+
| Authorization| YES | See |
| for making |------>| main |
| ES call | | diagram |
\ with / `......../
\ VSP/ASP? //
\\ //
\ //
\--/
|
| NO
|
|
v
+------------+
| Execute |
| ZBP |
| Procedures |
+------------+
|
| Call
| in progress
|
v
+--------+
| Call |
Success|
`......./
Figure 3: Flow Diagram: ZBP Scenario.
+-----+
+------------|Start|-----------------+
| `...../ |
v v
+------------+ +----------------+
| NAA | | Regular |
| Procedures | | Network Access |
+------------+ | Procedures |
| +----------------+
| |
| |
----------------o--------------------+
|
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|
|
|
Network
Attachment
Completed
|
|
|
|
v
+------------+ +---------+
| ASP | YES | See |
| Configured?|----->| main |
+------------+ | diagram |
| `......../
|
| NO
|
v
+------------+
| Execute |
| NASP |
| Procedures |
+------------+
|
| Call
| in progress
|
v
+--------+
| Call |
Success|
`......./
Figure 4: Flow Diagram: NASP Scenario.
The "No Access Authentication (NAA)" procedures are described in
Section 6. The "Zero-balance ASP (ZBP)" procedures are described in
Section 4. The "No ASP (NASP)" procedures are described in
Section 5. The Phone BCP procedures are described in [RFC6881]. The
"Link Layer Attachment (LLA)" procedures are not described in this
document since they are specific to the link layer technology in use.
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4. ZBP Considerations
ZBP includes all cases where a subscriber is known to an ASP, but
lacks the necessary authorization to access regular ASP services.
Example ZBP cases include empty prepaid accounts, barred accounts,
roaming and mobility restrictions, or any other conditions set by ASP
policy.
Local regulation might demand that emergency calls cannot proceed
without successful service authorization. In regulatory regimes,
however, it may be possible to allow emergency calls to continue
despite authorization failures. To distinguish an emergency call
from a regular call an ASP can identify emergency sessions by
inspecting the service URN [RFC5031] used in call setup. The ZBP
case therefore only affects the ASP.
Permitting a call despite authorization failures could present an
opportunity for abuse. The ASP may choose to verify the destination
of the emergency calls and to only permit calls to certain, pre-
configured entities (e.g., to local PSAPs). Section 7 discusses this
topic in more detail.
An ASP without a regulatory requirement to authorize emergency calls
can deny emergency call setup. Where an ASP does not authorize an
emergency call, the caller may be able to fall back to NASP
procedures.
5. NASP Considerations
To start the description we consider the sequence of steps that are
executed in an emergency call based on Figure 5.
o As an initial step the devices attaches to the network as shown in
step (1). This step is outside the scope of this section.
o When the link layer network attachment procedure is completed the
end host learns basic IP configuration information using DHCP from
the ISP, as shown in step (2).
o When the IP address configuration is completed then the end host
starts an interaction with the discovered Location Configuration
Server at the ISP, as shown in step (3). The ISP may in certain
deployments need to interact with the IAP. This protocol exchange
is shown in step (4).
o Once location information is obtained the end host triggers the
LoST protocol to obtain the address of the ESRP/PSAP. This step
is shown in (5).
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o In step (6), the SIP UA initiates a SIP INVITE towards the
indicated ESRP. The INVITE message contains all the necessary
parameters required by Section 5.1.5.
o The ESRP receives the INVITE and processes it according to the
description in Section 5.3.3.
o The ESRP routes the call to the PSAP, as shown in (8), potentially
interacting with a LoST server first to determine the route.
o The PSAP evaluates the initial INVITE and aims to complete the
call setup.
o Finally, when the call setup is completed media traffic can be
exchanged between the PSAP and the SIP UA.
For editorial reasons the end-to-end SIP and media exchange between
the PSAP and SIP UA are not shown in Figure 5.
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+-------+
| PSAP |
| |
+-------+
^
| (8)
|
+----------+(7) +----------+
| LoST |<-->| ESRP |
| Server | | |
+----------+ +----------+
^ ^
+----------------+----------------|--------------+
| ISP | | |
|+----------+ | | +----------+|
|| LCS-ISP | (3)| | | DHCP ||
|| |<-+ | | | Server ||
|+----------+ | | | +----------+|
+-------^------+-+----------------|-----------^--+
+-------|------+-+----------------|-----------|--+
| IAP | (4) | |(5) | | |
| V | | | | |
|+----------+ | | | | |
|| LCS-IAP | | | +--------+ | | |
|| | | | | Link | |(6) | |
|+----------+ | | | Layer | | | |
| | | | Device | | (2)| |
| | | +--------+ | | |
| | | ^ | | |
| | | | | | |
+--------------+-|-------|--------|-----------|--+
| | | | |
| | (1)| | |
| | | | |
| | | +----+ |
| | v | |
| | +----------+ |
| +->| End |<-------------+
+___>| Host |
+----------+
Figure 5: Architectural Overview
Note: Figure 5 does not indicate who operates the ESRP and the LoST
server. Various deployment options exist.
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5.1. End Host Profile
5.1.1. LoST Server Discovery
The end host MUST discover a LoST server [RFC5222] using DHCP
[RFC5223] unless a LoST server has been provisioned using other
means.
5.1.2. ESRP Discovery
The end host MUST discover the ESRP using the LoST protocol [RFC5222]
unless a ESRP has been provisioned using other means.
5.1.3. Location Determination and Location Configuration
The end host MUST support location acquisition and the LCPs described
in Section 6.5 of [RFC6881]. The description in Section 6.5 and 6.6
of [RFC6881] regarding the interaction between the device and the LIS
applies to this document.
The SIP UA in the end host MUST attach available location information
in a PIDF-LO [RFC4119] when making an emergency call. When
constructing the PIDF-LO the guidelines in PIDF-LO profile [RFC5491]
MUST be followed. For civic location information the format defined
in [RFC5139] MUST be supported.
5.1.4. Emergency Call Identification
To determine which calls are emergency calls, some entity needs to
map a user entered dialstring into this URN scheme. A user may
"dial" 1-1-2, 9-1-1, etc., but the call would be sent to
urn:service:sos. This mapping SHOULD be performed at the endpoint
device.
End hosts MUST use the Service URN mechanism [RFC5031] to mark calls
as emergency calls for their home emergency dial string.
5.1.5. SIP Emergency Call Signaling
SIP signaling capabilities [RFC3261] are REQUIRED for end hosts.
The initial SIP signaling method is an INVITE. The SIP INVITE
request MUST be constructed according to the requirements in
Section 9.2 [RFC6881].
Regarding callback behavior SIP UAs SHOULD place a globally routable
URI in a Contact: header.
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5.1.6. Media
End points MUST comply with the media requirements for end points
placing an emergency call found in Section 14 of [RFC6881].
5.1.7. Testing
The description in Section 15 of [RFC6881] is fully applicable to
this document.
5.2. IAP/ISP Profile
5.2.1. ESRP Discovery
An ISP MUST provision a DHCP server with information about LoST
servers [RFC5223]. An ISP operator may choose to deploy a LoST
server or to outsource it to other parties.
5.2.2. Location Determination and Location Configuration
The ISP is responsible for location determination and exposes this
information to the end points via location configuration protocols.
The considerations described in [RFC6444] are applicable to this
document.
The ISP MUST support one of the LCPs described in Section 6.5 of
[RFC6881]. The description in Section 6.5 and 6.6 of [RFC6881]
regarding the interaction between the end device and the LIS applies
to this document.
The interaction between the LIS at the ISP and the IAP is often
priorietary but the description in
[I-D.winterbottom-geopriv-lis2lis-req] may be relevant to the reader.
5.3. ESRP Profile
5.3.1. Emergency Call Routing
The ESRP continues to route the emergency call to the PSAP
responsible for the physical location of the end host. This may
require further interactions with LoST servers but depends on the
specific deployment.
5.3.2. Emergency Call Identification
The ESRP MUST understand the Service URN mechanism [RFC5031] (i.e.,
the 'urn:service:sos' tree).
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5.3.3. SIP Emergency Call Signaling
SIP signaling capabilities [RFC3261] are REQUIRED for the ESRP. The
ESRP MUST process the messages sent by the client, according to
Section 5.1.5.
Furthermore, if a PSAP wants to support NASP calls, then it MUST NOT
restrict incoming calls to a particular set of ASPs.
6. Lower Layer Considerations for NAA Case
Some networks have added support for unauthenticated emergency
access, some other type of networks advertise these capabilities
using layer beacons. The end host learns about these unauthenticated
emergency services capabilities either from the link layer type or
from advertisement.
It is important to highlight that the NAA case is inherently a layer
2 problem, and the general form of the solution is to provide an
"emergency only" access type, with appropriate limits/monitoring to
prevent abuse. The described mechanisms are informative in nature
since the relationship to the IETF emergency services architecture is
only indirect, namely via some protocols developed within the IETF
(e.g., EAP and EAP methods) that require extensions to support this
functionality.
This section discusses different methods to indicate an emergency
service request as part of network attachment. It provides some
general considerations and recommendations that are not specific to
the access technology.
To perform network attachment and get access to the resources
provided by an IAP/ISP, the end host uses access technology specific
network attachment procedures, including for example network
detection and selection, authentication, and authorization. For
initial network attachment of an emergency service requester, the
method of how the emergency indication is given to the IAP/ISP is
specific to the access technology. However, a number of general
approaches can be identified:
Link layer emergency indication: The end host provides an
indication, e.g., an emergency parameter or flag, as part of the
link layer signaling for initial network attachment. Examples
include an emergency bit signalled in the IEEE 802.16-2009
wireless link. In IEEE 802.11 WLAN, an emergency support
indicator allows the station (i.e., end host in this context) to
download before association a Network Access Identifier (NAI),
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which it can use to request server side authentication only for an
802.1x network.
Higher-layer emergency indication: Typically, emergency indication
is provided in the network access authentication procedure. The
emergency caller's end host provides an indication as part of the
access authentication exchanges. Authentication via the
Extensible Authentication Protocol (EAP) [RFC3748] is of
particular relevance here. Examples are the EAP NAI decoration
used in WiMAX networks and modification of the authentication
exchange in IEEE 802.11. [nwgstg3].
6.1. Link Layer Emergency Indication
In general, link layer emergency indications provide good integration
into the actual network access procedure regarding the enabling of
means to recognize and prioritize an emergency service request from
an end host at a very early stage of the network attachment
procedure. However, support in end hosts for such methods cannot be
considered to be commonly available.
No general recommendations are given in the scope of this memo due to
the following reasons:
o Dependency on the specific access technology.
o Dependency on the specific access network architecture. Access
authorization and policy decisions typically happen at a different
layers of the protocol stack and in different entities than those
terminating the link-layer signaling. As a result, link layer
indications need to be distributed and translated between the
different involved protocol layers and entities. Appropriate
methods are specific to the actual architecture of the IAP/ISP
network.
o An advantage of combining emergency indications with the actual
network attachment procedure performing authentication and
authorization is the fact that the emergency indication can
directly be taken into account in the authentication and
authorization server that owns the policy for granting access to
the network resources. As a result, there is no direct dependency
on the access network architecture that otherwise would need to
take care of merging link-layer indications into the AA and policy
decision process.
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o EAP signaling happens at a relatively early stage of network
attachment, so it is likely to match most requirements for
prioritization of emergency signaling. However, it does not cover
early stages of link layer activity in the network attachment
process. Possible conflicts may arise e.g. in case of MAC-based
filtering in entities terminating the link-layer signaling in the
network (like a base station). In normal operation, EAP related
information will only be recognized in the NAS. Any entity
residing between end host and NAS should not be expected to
understand/parse EAP messages.
o An emergency indication can be given by forming a specific NAI
that is used as the identity in EAP based authentication for
network entry.
6.2. Securing Network Attachment in NAA Cases
For network attachment in NAA cases, it may make sense to secure the
link-layer connection between the device and the IAP/ISP. This
especially holds for wireless access with examples being IEEE 802.11
or IEEE 802.16 based access. The latter even mandates secured
communication across the wireless link for all IAP/ISP networks based
on [nwgstg3].
Therefore, for network attachment that is by default based on EAP
authentication it is desirable also for NAA network attachment to use
a key-generating EAP method (that provides an MSK key to the
authenticator to bootstrap further key derivation for protecting the
wireless link).
The following approaches to match the above can be identified:
1) Server-only Authentication:
The device of the emergency service requester performs an EAP
method with the IAP/ISP EAP server that performs server side
authentication only. An example for this is EAP-TLS [RFC5216].
This provides a certain level of assurance about the IAP/ISP to
the device user. It requires the device to be provisioned with
appropriate trusted root certificates to be able to verify the
server certificate of the EAP server (unless this step is
explicitly skipped in the device in case of an emergency service
request). This method is used to provide access of devices
without existing credentials to an 802.1x network. The details
are incorporated into the not yet published 802.11-2011
specification.
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2) Null Authentication:
In one case (e.g., WiMAX) an EAP method is performed. However, no
credentials specific to either the server or the device or
subscription are used as part of the authentication exchange. An
example for this would be an EAP-TLS exchange with using the
TLS_DH_anon (anonymous) ciphersuite. Alternatively, a publicly
available static key for emergency access could be used. In the
latter case, the device would need to be provisioned with the
appropriate emergency key for the IAP/ISP in advance. In another
case (e.g., IEEE 802.11), no EAP method is used, so that empty
frames are transported during the over the air IEEE 802.1X
exchange. In this case the authentication state machine completes
with no cryptographic keys being exchanged.
3) Device Authentication:
This case extends the server-only authentication case. If the
device is configured with a device certificate and the IAP/ISP EAP
server can rely on a trusted root allowing the EAP server to
verify the device certificate, at least the device identity (e.g.,
the MAC address) can be authenticated by the IAP/ISP in NAA cases.
An example for this are WiMAX devices that are shipped with device
certificates issued under the global WiMAX device public-key
infrastructure. To perform unauthenticated emergency calls, if
allowed by the IAP/ISP, such devices perform EAP-TLS based network
attachment with client authentication based on the device
certificate.
7. Security Considerations
The security threats discussed in [RFC5069] are applicable to this
document.
There are a couple of new vulnerabilities raised with unauthenticated
emergency services in NASP/NAA cases since the PSAP operator will
typically not possess any identity information about the emergency
caller via the signaling path itself. In countries where this
functionality is used for GSM networks today this has lead to a
significant amount of misuse.
In the context of NAA, the IAP and the ISP will probably want to make
sure that the claimed emergency caller indeed performs an emergency
call rather than using the network for other purposes, and thereby
acting fraudulent by skipping any authentication, authorization and
accounting procedures. By restricting access of the unauthenticated
emergency caller to the LoST server and the PSAP URI, traffic can be
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restricted only to emergency calls. This can be accomplished with
traffic separation. The details, however, e.g. for using filtering,
depend on the deployed ISP architecture and are beyond the scope of
this document.
We only illustrate a possible model. If the ISP runs its own
(caching) LoST server, the ISP would maintain an access control list
populated with IP-address information obtained from LoST responses
(in the mappings). These URIs would either be URIs for contacting
further LoST servers or PSAP URIs. It may be necessary to translate
domain names returned in LoST responses to IP addresses. Since the
media destination addresses are not predictable, the ISP also has to
provide a SIP outbound proxy so that it can determine the media
addresses and add those to the filter list.
For the ZBP case the additional aspect of fraud has to be considered.
Unless the emergency call traverses a PSTN gateway or the ASP charges
for IP-to-IP calls, there is little potential for fraud. If the ASP
also operates the LoST server, the outbound proxy MAY restrict
outbound calls to the SIP URIs returned by the LoST server. It is
NOT RECOMMENDED to rely on a fixed list of SIP URIs, as that list may
change.
RFC 6280 [RFC6280] discusses security vulnerabilities that are caused
by an adversary faking location information and thereby lying about
the actual location of the emergency caller. These threats may be
less problematic in the context of unauthenticated emergency when
location information can be verified by the ISP to fall within a
specific geographical area.
8. Acknowledgments
Parts of this document are derived from [RFC6881]. Participants of
the 2nd and 3rd SDO Emergency Services Workshop provided helpful
input.
We would like to thank Richard Barnes, Brian Rosen, James Polk, Marc
Linsner, and Martin Thomson for their feedback at the IETF#80 ECRIT
meeting.
Furthermore, we would like to thank Martin Thomson and Bernard Aboba
for their detailed document review in preparation of the 81st IETF
meeting. Alexey Melnikov was the General Area (Gen-Art) reviewer. A
number of changes to the document had been made in response to the AD
review by Richard Barnes.
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We would also like to thank review comments from various IESG
members, including Stephen Farrell, Barry Leiba, Pete Resnick,
Spencer Dawkins, Joel Jaeggli, and Ted Lemon.
9. IANA Considerations
This document does not require actions by IANA.
10. References
10.1. Normative References
[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services", RFC 5031,
January 2008.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[RFC5491] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
Presence Information Data Format Location Object (PIDF-LO)
Usage Clarification, Considerations, and Recommendations",
RFC 5491, March 2009.
[RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location
Format for Presence Information Data Format Location
Object (PIDF-LO)", RFC 5139, February 2008.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6881] Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in Support of Emergency Calling",
BCP 181, RFC 6881, March 2013.
[RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, August 2008.
[RFC5223] Schulzrinne, H., Polk, J., and H. Tschofenig, "Discovering
Location-to-Service Translation (LoST) Servers Using the
Dynamic Host Configuration Protocol (DHCP)", RFC 5223,
August 2008.
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10.2. Informative References
[RFC5687] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
Location Configuration Protocol: Problem Statement and
Requirements", RFC 5687, March 2010.
[RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
"Framework for Emergency Calling Using Internet
Multimedia", RFC 6443, December 2011.
[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for
Emergency Context Resolution with Internet Technologies",
RFC 5012, January 2008.
[RFC6444] Schulzrinne, H., Liess, L., Tschofenig, H., Stark, B., and
A. Kuett, "Location Hiding: Problem Statement and
Requirements", RFC 6444, January 2012.
[I-D.winterbottom-geopriv-lis2lis-req]
Winterbottom, J. and S. Norreys, "LIS to LIS Protocol
Requirements", draft-winterbottom-geopriv-lis2lis-req-01
(work in progress), November 2007.
[RFC5069] Taylor, T., Tschofenig, H., Schulzrinne, H., and M.
Shanmugam, "Security Threats and Requirements for
Emergency Call Marking and Mapping", RFC 5069, January
2008.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004.
[RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
Authentication Protocol", RFC 5216, March 2008.
[RFC6280] Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
Tschofenig, H., and H. Schulzrinne, "An Architecture for
Location and Location Privacy in Internet Applications",
BCP 160, RFC 6280, July 2011.
[esw07] "3rd SDO Emergency Services Workshop,
http://www.emergency-services-coordination.info/2007Nov/",
October 30th - November 1st 2007.
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[nwgstg3] "WiMAX Forum WMF-T33-001-R015V01, WiMAX Network
Architecture Stage-3
http://www.wimaxforum.org/sites/wimaxforum.org/files/
technical_document/2009/09/DRAFT-T33-001-R015v01-
O_Network-Stage3-Base.pdf", September 2009.
Authors' Addresses
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
Email: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu
Stephen McCann
Research in Motion UK Ltd
200 Bath Road
Slough, Berks SL1 3XE
UK
Phone: +44 1753 667099
Email: smccann@rim.com
URI: http://www.rim.com
Gabor Bajko
Email: gaborbajko@gmail.com
Hannes Tschofenig
Hall in Tirol 6060
Austria
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
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Dirk Kroeselberg
Siemens
Germany
Email: dirk.kroeselberg@siemens.com
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