ECRIT H. Schulzrinne
Internet-Draft Columbia University
Intended status: Standards Track S. McCann
Expires: March 25, 2011 Research in Motion UK Ltd
G. Bajko
Nokia
H. Tschofenig
D. Kroeselberg
Nokia Siemens Networks
September 21, 2010
Extensions to the Emergency Services Architecture for dealing with
Unauthenticated and Unauthorized Devices
draft-ietf-ecrit-unauthenticated-access-00.txt
Abstract
The IETF emergency services architecture assumes that the calling
device has acquired rights to use the access network or that no
authentication is required for the access network, such as for public
wireless access points. Subsequent protocol interactions, such as
obtaining location information, learning the address of the Public
Safety Answering Point (PSAP) and the emergency call itself are
largely decoupled from the underlying network access procedures.
In some cases, the device does not have credentials for network
access, does not have a VoIP provider or application service provider
(ASP), or the credentials have become invalid, e.g., because the user
has exhausted their prepaid balance or the account has expired.
This document provides a problem statement, introduces terminology
and describes an extension for the base IETF emergency services
architecture to address these scenarios.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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
Schulzrinne, et al. Expires March 25, 2011 [Page 1]
Internet-Draft Unauthenticated Emergency Service September 2010
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 25, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Schulzrinne, et al. Expires March 25, 2011 [Page 2]
Internet-Draft Unauthenticated Emergency Service September 2010
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. No Access Authorization (NAA) . . . . . . . . . . . . . . 5
1.2. No ASP (NASP) . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Zero-Balance Application Service Provider (ZBP) . . . . . 6
2. A Warning Note . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Considerations for ISPs to support Unauthenticated
Emergency Services without Architecture Extensions . . . . . . 7
5. Considerations for ISPs to support Unauthenticated
Emergency Services with Architecture Extensions . . . . . . . 8
6. NAA considerations for the network attachment procedure of
IAPs/ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Link layer emergency indication . . . . . . . . . . . . . 12
6.2. Higher-layer emergency indication . . . . . . . . . . . . 13
6.3. Securing network attachment in NAA cases . . . . . . . . . 14
7. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. End Host Profile . . . . . . . . . . . . . . . . . . . . . 16
7.1.1. LoST Server Discovery . . . . . . . . . . . . . . . . 16
7.1.2. ESRP Discovery . . . . . . . . . . . . . . . . . . . . 16
7.1.3. Location Determination and Location Configuration . . 16
7.1.4. Emergency Call Identification . . . . . . . . . . . . 16
7.1.5. SIP Emergency Call Signaling . . . . . . . . . . . . . 17
7.1.6. Media . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1.7. Testing . . . . . . . . . . . . . . . . . . . . . . . 17
7.2. IAP/ISP Profile . . . . . . . . . . . . . . . . . . . . . 17
7.2.1. ESRP Discovery . . . . . . . . . . . . . . . . . . . . 17
7.2.2. Location Determination and Location Configuration . . 17
7.3. ESRP Profile . . . . . . . . . . . . . . . . . . . . . . . 18
7.3.1. Emergency Call Routing . . . . . . . . . . . . . . . . 18
7.3.2. Emergency Call Identification . . . . . . . . . . . . 18
7.3.3. SIP Emergency Call Signaling . . . . . . . . . . . . . 18
7.3.4. Location Retrieval . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
Schulzrinne, et al. Expires March 25, 2011 [Page 3]
Internet-Draft Unauthenticated Emergency Service September 2010
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
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, which 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
[I-D.ietf-ecrit-phonebcp] and [I-D.ietf-ecrit-framework]) divides
responsibility for handling emergency calls between the access
network (ISP), the application service provider (ASP) that may be a
VoIP service provider 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 MUST 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 between three conditions:
No access authorization (NAA): The current access network requires
access authorization and the caller does not have valid user
credentials. (This includes the case where the access network
allows pay-per-use, as is common for wireless hotspots, but there
is insufficient time to pay for access.)
Schulzrinne, et al. Expires March 25, 2011 [Page 4]
Internet-Draft Unauthenticated Emergency Service September 2010
No ASP (NASP): The caller does not have an ASP at the time of the
call.
Zero-balance ASP (ZBP): The caller has valid credentials with an
ASP, but is not allowed to access services like placing calls in
case of a VoIP service, e.g., because the user has a zero balance
in a prepaid account.
A user may well suffer from both NAA and NASP or ZBP at the same
time. 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,
a caller should be able to place an emergency call in the ZBP case.
We discuss each case in separate sections below.
1.1. No Access Authorization (NAA)
In the NAA (No Access Authorization) case, the emergency caller does
not posses valid credentials for the access network. If local
regulations or policy allows or requires support for emergency calls
in NAA, the access network may or needs to cooperate in providing
emergency calling services. Support for NAA emergency calls 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. Hence, no global mandates for
supporting emergency calls in relation to NAA can be made. However,
it makes a lot of sense to offer appropriate building blocks that
enable ISPs to flexibly react on the local environment.Generally, the
ISP will want to ensure that devices do not pretend to place
emergency calls, but then abuse the access for obtaining more general
services fraudulently.
In particular, the ISP MUST allow emergency callers to acquire an IP
address and to reach a LoST server, either provided by the ISP or
some third party. It SHOULD also provide location information via
one of the mechanisms specified in [I-D.ietf-ecrit-phonebcp] without
requiring authorization unless it can safely assume that all nodes in
the access network can determine their own location, e.g., via GPS.
The details of how filtering is performed depends on the details of
the ISP architecture and are beyond the scope of this document. We
illustrate a possible model. If the ISP runs its own LoST server, it
would maintain an access control list including all IP addresses
contained in responses returned by the LoST server, as well as the
LoST server itself. (It may need to translate the domain names
Schulzrinne, et al. Expires March 25, 2011 [Page 5]
Internet-Draft Unauthenticated Emergency Service September 2010
returned to IP addresses and hope that the resolution captures all
possible DNS responses.) 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.
1.2. No ASP (NASP)
In the second case, the emergency caller has no current ASP. This
case poses no particular difficulties unless it is assumed that only
ASPs provide LoST server or that ESNs only accept calls that reach it
through a set of known ASPs. However, since the calling device
cannot obtain configuration information from its ASP, the ISP MUST
provide the address of a LoST server via DHCP [RFC5223] if this model
is to be supported. The LoST server may be operated either by the
ISP or a third party.
1.3. Zero-Balance Application Service Provider (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. Naturally, an ASP can simply disallow access by such
customers, so that all such customers find themselves in the NASP
situation described above. If ASPs desire or are required by
regulation to provide emergency calling services to such customers,
they need to provide LoST services to such customers and may need to
provide outbound SIP proxy services. As usual, the calling device
looks up the LoST server via SIP configuration.
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.
2. A Warning Note
At the time of writing there is no regulation in place that demands
the functionality described in this memo. SDOs have started their
work on this subject in a proactive fashion in the anticipation that
national regulation will demand it for a subset of network
environments.
There are also indications that the functionality of unauthenticated
emergency calls (called SIM-less calls) in today's cellular system in
Schulzrinne, et al. Expires March 25, 2011 [Page 6]
Internet-Draft Unauthenticated Emergency Service September 2010
certain countries leads to a fair amount of hoax or test calls. 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].
3. 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 [I-D.ietf-geopriv-l7-lcp-ps]
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.
4. Considerations for ISPs to support Unauthenticated Emergency
Services without Architecture Extensions
This section provides a recommended configuration for unauthenticated
emergency services support without architecture extensions.
On a very high-level, the steps to be performed by an end host not
being attached to the network and the user starting to make an
emergency call are the following:
o Some radio 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.
o The end host uses the link layer specific network attachment
procedures defined for unauthenticated network access in order to
get access to emergency services.
Schulzrinne, et al. Expires March 25, 2011 [Page 7]
Internet-Draft Unauthenticated Emergency Service September 2010
o When the link layer network attachment procedure is completed the
end host learns basic configuration information using DHCP from
the ISP, including the address of the LoST server.
o The end host MUST use a Location Configuration Protocol (LCP)
supported by the IAP or ISP to learn its own location.
o The end host MUST use the LoST protocol [I-D.ietf-ecrit-lost] to
query the LoST server and asks for the PSAP URI responsible for
that location.
o After the PSAP URI has been returned to the end host, the SIP UA
in the end host directly initiates a SIP INVITE towards the PSAP
URI.
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 restricted only to
emergency calls (see also section 1.1).
Using the above procedures, the unauthenticated emergency caller will
be successful only if:
o the ISP (or the IAP) support an LCP that the end host can use to
learn its location. A list of mandatory-to-implement LCPs can be
found in [I-D.ietf-ecrit-phonebcp]).
o the ISP configures it's firewalls appropriately to allow emergency
calls to traverse the network towards the PSAP.
Some IAPs/ISPs may not be able to fulfill the above requirements. If
those IAPs/ISPs want to support unauthenticated emergency calls, then
they can deploy an extended architecture as described in Section 5.
5. Considerations for ISPs to support Unauthenticated Emergency
Services with Architecture Extensions
This section provides a recommended configuration for unauthenticated
emergency services support without architecture extensions.
For unauthenticated emergency services support it is insufficient to
provide mechanisms only at the link layer in order to bypass
authentication for the cases when:
o the IAP/ISP does not support any Location Configuration Protocol
o the IAP/ISP cannot assume the end hosts to support a Location
Configuration Protocol
Schulzrinne, et al. Expires March 25, 2011 [Page 8]
Internet-Draft Unauthenticated Emergency Service September 2010
o the IAP/ISP does not have knowledge of a LoST server (which would
assist the client to find the correct PSAP)
A modification to the emergency services architecture is necessary
since the IAP and the ISP need 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.
Hence, without introducing some understanding of the specific
application the ISP (and consequently the IAP) will not be able to
detect and filter malicious activities. This leads to the
architecture described in Figure 1 where the IAP needs to implement
extensions to link layer procedures for unauthenticated emergency
service access and the ISP needs to deploy emergency services related
entities used for call routing, such as the Emergency Services
Routing Proxy (ESRP), a Location Configuration Server (LCS) and a
mapping database.
On a very high-level, the interaction is as follows starting with the
end host not being attached to the network and the user starting to
make an emergency call.
o Some radio 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.
o The end host uses the link layer specific network attachment
procedures defined for unauthenticated network access in order to
get access to emergency services.
o When the link layer network attachment procedure is completed the
end host learns basic configuration information using DHCP from
the ISP, including the address of the ESRP, as shown in (2).
o When the IP address configuration is completed then the SIP UA
initiates a SIP INVITE towards the indicated ESRP, as shown in
(3). The INVITE message contains all the necessary parameters
required by Section 7.1.5.
o The ESRP receives the INVITE and processes it according to the
description in Section 7.3.3. The location of the end host may
need to be determined using a protocol interaction shown in (4).
o Potentially, an interaction between the LCS of the ISP and the LCS
of the IAP may be necessary, see (5).
o Finally, the correct PSAP for the location of the end host has to
be evaluated, see (6).
o The ESRP routes the call to the PSAP, as shown in (7).
o The PSAP evaluates the initial INVITE and aims to complete the
call setup.
Schulzrinne, et al. Expires March 25, 2011 [Page 9]
Internet-Draft Unauthenticated Emergency Service September 2010
o Finally, when the call setup is completed media traffic can be
exchanged between the PSAP and the emergency caller.
For editorial reasons the end-to-end SIP and media exchange between
the PSAP and SIP UA are not shown in Figure 1.
Two important aspects are worth to highlight:
o The IAP/ISP needs to understand the concept of emergency calls or
other emergency applicationsand the SIP profile described in this
document. No other VoIP protocol profile, such as XMPP, Skype,
etc., are supported for emergency calls in this particular
architecture. Other profiles may be added in the future, but the
deployment effort is enormous since they have to be universally
deployed.
o The end host has no obligation to determine location information.
It may attach location information if it has location available
(e.g., from a GPS receiver).
Figure 1 shows that the ISP needs to deploy SIP-based emergency
services functionality. It is important to note that the ISP itself
may outsource the functionality by simply providing access to them
(e.g., it puts the IP address of an ESRP or a LoST server into an
allow-list). For editorial reasons this outsourcing is not shown.
Schulzrinne, et al. Expires March 25, 2011 [Page 10]
Internet-Draft Unauthenticated Emergency Service September 2010
+---------------------------+
| |
| Emergency Network |
| Infrastructure |
| |
| +----------+ +----------+ |
| | PSAP | | ESRP | |
| | | | | |
| +----------+ +----------+ |
+-------------------^-------+
|
| (7)
+------------------------+-----------------------+
| ISP | |
| | |
|+----------+ v |
|| Mapping | (6) +----------+ |
|| Database |<----->| ESRP / | |
|+----------+ | SIP Proxy|<-+ |
|+----------+ +----------+ | +----------+|
|| LCS-ISP | ^ | | DHCP ||
|| |<---------+ | | Server ||
|+----------+ (4) | +----------+|
+-------^-------------------------+-----------^--+
+-------|-------------------------+-----------|--+
| IAP | (5) | | |
| V | | |
|+----------+ | | |
|| LCS-IAP | +----------+ | | |
|| | | Link | |(3) | |
|+----------+ | Layer | | | |
| | Device | | (2)| |
| +----------+ | | |
| ^ | | |
| | | | |
+------------------------+--------+-----------+--+
| | |
(1)| | |
| | |
| +----+ |
v v |
+----------+ |
| End |<-------------+
| Host |
+----------+
Figure 1: Overview
Schulzrinne, et al. Expires March 25, 2011 [Page 11]
Internet-Draft Unauthenticated Emergency Service September 2010
It is important to note that a single ESRP may also offer it's
service to several ISPs.
6. NAA considerations for the network attachment procedure of IAPs/ISPs
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.
signalling allows an IEEE 802.1X to occur without exchanging
cryptogrpahic keys
- Higher-layer emergency indication: Typically emergency indication
in access authentication. The emergency caller's end host provides
an indication as part of the access authentication exchanges. EAP
based authentication is of particular relevance here. [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:
- Dependency on the specific access technology.
- Dependency on the specific access network architecture. Access
authorization and policy decisions typically happen at a different
Schulzrinne, et al. Expires March 25, 2011 [Page 12]
Internet-Draft Unauthenticated Emergency Service September 2010
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.
6.2. Higher-layer emergency indication
This section focuses on emergency indications based on authentication
and authorization in EAP-based network access.
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.
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.
The following potential methods to provide emergency indications in
combination with EAP-based network attachment, are recognized:
1) NAI-based emergency indication:
An emergency indication can be given by forming a specific NAI that
is used as the identity in EAP based authentication for network
entry. Methods include:
1.a) NAI Decoration: NAI decoration is commonly used in routing EAP
responses within the IAP/ISP AAA infrastructure. Additional
decoration can be used to add an indication that the network
attachment attempt is meant for accessing emergency services.
Potential advantages of such approach include that it requires only
minimal realization effort compared to link-layer indications with
good integration into the authentication and authorization
procedures. The same procedure can be used for all NAA cases (both
Schulzrinne, et al. Expires March 25, 2011 [Page 13]
Internet-Draft Unauthenticated Emergency Service September 2010
unauthenticated and unauthorized) as well as for normal attachment
with a valid subscription. A potential disadvantage is that such EAP
decoration is not globally defined across all different access
technologies.
1.b) Emergency NAI: The NAI comes with a realm or username part
indicating emergency (e.g. 'emergency@emergency.com'). An advantage
of this method for NAA cases is that no new requirements are put on
the involved signaling procedures. Only the identity used for
network entry is impacted. Potential disadvantages include that
different methods to indicate emergency for NAA cases and standard
emergency network attachments may be required. Also, modifying the
NAI itself (the username@realm part) may conflict with network
selection and network entry procedures, depending on the actual
access network.
2) Emergency EAP method
An emergency indication can be given by using a dedicated EAP method
that is reserved for emergency network attachment only.
2.a) Existing EAP method with new type: An existing EAP method may be
used. EAP methods themselves typically do not support emergency
indication. One option would be to pick a common EAP method like
EAP-TLS and allocate a new method type for the same method that is
exclusively reserved to emergency use. Such EAP method should be
chosen in a way that the same method can support NAA cases as well as
standard emergency network attachment.
2.b) Existing EAP method: Same as 2a), but without assigning a new
EAP method type for emergency. In this case some implicit indication
must be used. For example, in cases where EAP-TLS is used in network
attachment in combination with client certificates, the absence of a
client certificate could be interpreted by the network as a request
for emergency network attachment.
2.c) Emergency EAP method: A new EAP method could be defined that is
specifically designed for emergency network entry in NAA cases. Most
likely, such EAP method would not be usable for standard emergency
network attachment with an existing subscription. Such dedicated
emergency EAP method should be key-generating in compliance with
RFC3748 to enable the regular air interface security methods even in
unauthenticated operation.
6.3. 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
Schulzrinne, et al. Expires March 25, 2011 [Page 14]
Internet-Draft Unauthenticated Emergency Service September 2010
especially holds for wireless access with examples being 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 authentication only. An example for this is EAP-TLS.
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).
2) Null authentication: 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.
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. Profiles
Schulzrinne, et al. Expires March 25, 2011 [Page 15]
Internet-Draft Unauthenticated Emergency Service September 2010
7.1. End Host Profile
7.1.1. LoST Server Discovery
The end host MAY attempt to use [I-D.ietf-ecrit-lost] to discover a
LoST server. If that attempt fails, the end host SHOULD attempt to
discover the address of an ESRP.
7.1.2. ESRP Discovery
The end host only needs an ESRP when location configuration or LoST
server discovery fails. If that is the case, then the end host MUST
use the "Dynamic Host Configuration Protocol (DHCP-for-IPv4) Option
for Session Initiation Protocol (SIP) Servers" [RFC3361] (for IPv6)
and / or the "Dynamic Host Configuration Protocol (DHCPv6) Options
for Session Initiation Protocol (SIP) Servers" [RFC3319] to discover
the address of an ESRP. This SIP proxy located in the ISP network
will be used as the ESRP for routing emergency calls. There is no
need to discovery a separate SIP proxy with specific emergency call
functionality since the internal procedure for emergency call
processing is subject of ISP internal operation.
7.1.3. Location Determination and Location Configuration
The end host SHOULD attempt to use the supported LCPs to configure
its location. If no LCP is supported in the end host or the location
configuration is not successful, then the end host MUST attempt to
discover an ESRP, which would assist the end host in providing the
location to the PSAP.
The SIP UA in the end host SHOULD attach the location information in
a PIDF-LO [RFC4119] when making an emergency call. When constructing
the PIDF-LO the guidelines in PIDF-LO profile
[I-D.ietf-geopriv-pdif-lo-profile] MUST be followed. For civic
location information the format defined in [RFC5139] MUST be
supported.
7.1.4. 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, 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 (if known).
For visited emergency dial string the translation into the Service
URN mechanism is not mandatory since the ESRP in the ISPs network
Schulzrinne, et al. Expires March 25, 2011 [Page 16]
Internet-Draft Unauthenticated Emergency Service September 2010
knows the visited emergency dial strings.
7.1.5. SIP Emergency Call Signaling
SIP signaling capabilities [RFC3261] are mandated 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 [I-D.ietf-ecrit-phonebcp].
Regarding callback behavior SIP UAs MUST have a globally routable URI
in a Contact: header.
7.1.6. Media
End points MUST comply with the media requirements for end points
placing an emergency call found in Section 14 of
[I-D.ietf-ecrit-phonebcp].
7.1.7. Testing
The description in Section 15 of [I-D.ietf-ecrit-phonebcp] is fully
applicable to this document.
7.2. IAP/ISP Profile
7.2.1. ESRP Discovery
An ISP hosting an ESRP MUST implement the server side part of
"Dynamic Host Configuration Protocol (DHCP-for-IPv4) Option for
Session Initiation Protocol (SIP) Servers" [RFC3361] (for IPv4) and /
or the "Dynamic Host Configuration Protocol (DHCPv6) Options for
Session Initiation Protocol (SIP) Servers" [RFC3319].
7.2.2. Location Determination and Location Configuration
The ISP not hosting an ESRP MUST support at least one widely used
LCP. The ISP hosting an ESRP MUST perform the neccesary steps to
determine the location of the end host. It is not necessary to
standardize a specific mechanism.
The role of the ISP is to operate the LIS. The usage of HELD
[I-D.ietf-geopriv-http-location-delivery] with the identity
extensions [I-D.ietf-geopriv-held-identity-extensions] may be a
possible choice. It might be necessary for the ISP to talk to the
IAP in order to determine the location of the end host. The work on
LIS-to-LIS communication may be relevant, see
[I-D.winterbottom-geopriv-lis2lis-req].
Schulzrinne, et al. Expires March 25, 2011 [Page 17]
Internet-Draft Unauthenticated Emergency Service September 2010
7.3. ESRP Profile
7.3.1. Emergency Call Routing
The ESRP must route the emergency call to the PSAP responsible for
the physical location of the end host. However, a standardized
approach for determining the correct PSAP based on a given location
is useful but not mandatory.
For cases where a standardized protocol is used LoST
[I-D.ietf-ecrit-lost] is a suitable mechanism.
7.3.2. Emergency Call Identification
The ESRP MUST understand the Service URN mechanism [RFC5031] (i.e.,
the 'urn:service:sos' tree) and additionally the national emergency
dial strings. The ESRP SHOULD perform a mapping of national
emergency dial strings to Service URNs to simplify processing at
PSAPs.
7.3.3. SIP Emergency Call Signaling
SIP signaling capabilities [RFC3261] are mandated for the ESRP. The
ESRP MUST process the messages sent by the client, according to
Section 7.1.5. Furthermore, the ESRP MUST be able to add a reference
to location information, as described in SIP Location Conveyance
[I-D.ietf-sip-location-conveyance], before forwarding the call to the
PSAP. The ISP MUST be prepared to receive incoming dereferencing
requests to resolve the reference to the location information.
7.3.4. Location Retrieval
The ESRP acts a location recipient and the usage of HELD
[I-D.ietf-geopriv-http-location-delivery] with the identity
extensions [I-D.ietf-geopriv-held-identity-extensions] may be a
possible choice. The ESRP would thereby act as a HELD client and the
corresponding LIS at the ISP as the HELD server.
The ESRP needs to obtain enough information to route the call. The
ESRP itself, however, does not necessarily need to process location
information obtained via HELD since it may be used as input to LoST
to obtain the PSAP URI.
8. Security Considerations
The security threats discussed in [RFC5069] are applicable to this
document. A number of security vulnerabilities discussed in
Schulzrinne, et al. Expires March 25, 2011 [Page 18]
Internet-Draft Unauthenticated Emergency Service September 2010
[I-D.ietf-geopriv-arch] around faked location information are less
problematic in this case since location information does not need to
be provided by the end host itself or it can be verified to fall
within a specific geographical area.
There are a couple of new vulnerabilities raised with unauthenticated
emergency services since the PSAP operator does is not in possession
of any identity information about the emergency call 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.
The link layer mechanisms need to provide a special way of handling
unauthenticated emergency services. Although this subject is not a
topic for the IETF itself but there are at least a few high-level
assumptions that may need to be collected. This includes security
features that may be desirable.
9. Acknowledgments
Section 6 of this document is derived from [I-D.ietf-ecrit-phonebcp].
The WiMax Forum contributed parts of the terminology. Participants
of the 2nd and 3rd SDO Emergency Services Workshop provided helpful
input.
10. IANA Considerations
This document does not require actions by IANA.
11. References
11.1. Normative References
[I-D.ietf-sip-location-conveyance]
Polk, J. and B. Rosen, "Location Conveyance for the
Session Initiation Protocol",
draft-ietf-sip-location-conveyance-13 (work in progress),
March 2009.
[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.
Schulzrinne, et al. Expires March 25, 2011 [Page 19]
Internet-Draft Unauthenticated Emergency Service September 2010
[I-D.ietf-geopriv-pdif-lo-profile]
Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
PIDF-LO Usage Clarification, Considerations and
Recommendations", draft-ietf-geopriv-pdif-lo-profile-14
(work in progress), November 2008.
[RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location
Format for Presence Information Data Format Location
Object (PIDF-LO)", RFC 5139, February 2008.
[RFC3361] Schulzrinne, H., "Dynamic Host Configuration Protocol
(DHCP-for-IPv4) Option for Session Initiation Protocol
(SIP) Servers", RFC 3361, August 2002.
[RFC3319] Schulzrinne, H. and B. Volz, "Dynamic Host Configuration
Protocol (DHCPv6) Options for Session Initiation Protocol
(SIP) Servers", RFC 3319, July 2003.
[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.
[I-D.ietf-ecrit-phonebcp]
Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in support of Emergency Calling",
draft-ietf-ecrit-phonebcp-15 (work in progress),
July 2010.
[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.
11.2. Informative References
[I-D.ietf-ecrit-lost]
Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", draft-ietf-ecrit-lost-10 (work in progress),
May 2008.
Schulzrinne, et al. Expires March 25, 2011 [Page 20]
Internet-Draft Unauthenticated Emergency Service September 2010
[I-D.ietf-geopriv-l7-lcp-ps]
Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
Location Configuration Protocol; Problem Statement and
Requirements", draft-ietf-geopriv-l7-lcp-ps-10 (work in
progress), July 2009.
[I-D.ietf-ecrit-framework]
Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
"Framework for Emergency Calling using Internet
Multimedia", draft-ietf-ecrit-framework-11 (work in
progress), July 2010.
[I-D.ietf-geopriv-http-location-delivery]
Barnes, M., Winterbottom, J., Thomson, M., and B. Stark,
"HTTP Enabled Location Delivery (HELD)",
draft-ietf-geopriv-http-location-delivery-16 (work in
progress), August 2009.
[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for
Emergency Context Resolution with Internet Technologies",
RFC 5012, January 2008.
[I-D.ietf-geopriv-held-identity-extensions]
Winterbottom, J., Thomson, M., Tschofenig, H., and R.
Barnes, "Use of Device Identity in HTTP-Enabled Location
Delivery (HELD)",
draft-ietf-geopriv-held-identity-extensions-04 (work in
progress), June 2010.
[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.
[I-D.ietf-geopriv-arch]
Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
Tschofenig, H., and H. Schulzrinne, "An Architecture for
Location and Location Privacy in Internet Applications",
draft-ietf-geopriv-arch-02 (work in progress), May 2010.
[esw07] "3rd SDO Emergency Services Workshop,
http://www.emergency-services-coordination.info/2007Nov/",
October 30th - November 1st 2007.
Schulzrinne, et al. Expires March 25, 2011 [Page 21]
Internet-Draft Unauthenticated Emergency Service September 2010
[nwgstg3] "WiMAX Forum WMF-T33-001-R015V01, WiMAX Network
Architecture Stage-3
http://www.wimaxforum.org/sites/wimaxforum.org/files/ tech
nical_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
Nokia
Email: Gabor.Bajko@nokia.com
Schulzrinne, et al. Expires March 25, 2011 [Page 22]
Internet-Draft Unauthenticated Emergency Service September 2010
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Dirk Kroeselberg
Nokia Siemens Networks
St.-Martin-Str. 76
Munich 81541
Germany
Phone: +49 (89) 515933019
Email: Dirk.Kroeselberg@nsn.com
Schulzrinne, et al. Expires March 25, 2011 [Page 23]
