ECRIT H. Schulzrinne
Internet-Draft Columbia University
Intended status: Standards Track S. McCann
Expires: April 28, 2011 Research in Motion UK Ltd
G. Bajko
Nokia
H. Tschofenig
D. Kroeselberg
Nokia Siemens Networks
October 25, 2010
Extensions to the Emergency Services Architecture for dealing with
Unauthenticated and Unauthorized Devices
draft-ietf-ecrit-unauthenticated-access-01.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, however, the device does not have these credentials
for network access, does not have a VoIP service provider, 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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 28, 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Use Case Categories . . . . . . . . . . . . . . . . . . . . . 6
4. ZBP Considerations . . . . . . . . . . . . . . . . . . . . . . 8
5. NASP Considerations . . . . . . . . . . . . . . . . . . . . . 9
5.1. End Host Profile . . . . . . . . . . . . . . . . . . . . . 11
5.1.1. LoST Server Discovery . . . . . . . . . . . . . . . . 11
5.1.2. ESRP Discovery . . . . . . . . . . . . . . . . . . . . 11
5.1.3. Location Determination and Location Configuration . . 11
5.1.4. Emergency Call Identification . . . . . . . . . . . . 11
5.1.5. SIP Emergency Call Signaling . . . . . . . . . . . . . 12
5.1.6. Media . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1.7. Testing . . . . . . . . . . . . . . . . . . . . . . . 12
5.2. IAP/ISP Profile . . . . . . . . . . . . . . . . . . . . . 12
5.2.1. ESRP Discovery . . . . . . . . . . . . . . . . . . . . 12
5.2.2. Location Determination and Location Configuration . . 12
5.3. ESRP Profile . . . . . . . . . . . . . . . . . . . . . . . 13
5.3.1. Emergency Call Routing . . . . . . . . . . . . . . . . 13
5.3.2. Emergency Call Identification . . . . . . . . . . . . 13
5.3.3. SIP Emergency Call Signaling . . . . . . . . . . . . . 13
5.3.4. Location Retrieval . . . . . . . . . . . . . . . . . . 13
6. Lower Layer Considerations for NAA Case . . . . . . . . . . . 14
6.1. Link Layer Emergency Indication . . . . . . . . . . . . . 14
6.2. Higher-Layer Emergency Indication . . . . . . . . . . . . 15
6.3. Securing Network Attachment in NAA Cases . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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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 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 between 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
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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.
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 for
help may find himself/herself in, for example, a NAA and NASP
situation, as explained in more details 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.
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
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
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functionality was disabled again. More details can be found in the
panel presentations of the 3rd SDO Emergency Services Workshop
[esw07].
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 not
being attached to the network and the user starting to make an
emergency call are the following:
Link Layer Attachment: 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.
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, including the
address of the LoST server. 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.
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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.
+-----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| |
Emergency Call? | |
+--------------+ v
| NO | YES +-----Y
| | | Done|
v v `...../
+------------+ +------------+
| Execute | | Execute |
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| ZBP | | Phone BCP |
| Procedures | | Procedures |
+------------+ +------------+
| |
| |
v v
+-----Y +-----Y
| Done| | Done|
`...../ `...../
Abbreviations:
LLA: Link Layer Attachment
ES: Emergency Services
Figure 1: Flow Diagram
4. ZBP Considerations
Although subject to local regulatory mandates, it is expected that
for most ASPs even with a lack of authorization for regular service
an otherwise authenticated and known subscriber must be granted
access to emergency services. Naturally, without an obligation to
support emergency services in ZBP cases an ASP can simply disallow
access by such customers. As a result, all such subscribers may fall
back into a NASP situation as described above.
If ASPs desire or are required by regulation to provide emergency
services to subscribers with valid credentials that only fail
authorization, the emergency services nature of a call can easily be
determined by inspecting the call setup procedure for the presence of
the emergency service URNs. This example shows that in the context
of this document no specific considerations apply to the ZBP case due
to the fact that the ASP will be able to relate the service request
to an existing subscription or user and will be in control of
adjusting any authorization decision based on its deployemnt specific
policy. It is, however, noted that specific security considerations
apply due to the fact that emergency service access will likely be
granted with limited authorization only, see Section 7.
ZBP cases in the context of this document cover all cases where an
otherwise valid subscription lacks authorization to access or regular
ASP services, i.e., a lack of authorization that would block the
subscriber from using the service for emergency purpose. Example ZBP
cases include empty prepaid accounts, barred accounts, or certain
roaming or mobility restrictions. The exact list of cases where
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emergency services need to be supported by the ASP is local to the
ASP policy and deployment, and is therefore beyond the scope of this
document.
5. NASP Considerations
To start the description we consider the sequence of steps that are
executed in an emergency call based on Figure 2.
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 configuration information using DHCP from
the ISP, including the address of the ESRP, as shown in step (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 5.1.5.
o The ESRP receives the INVITE and processes it according to the
description in Section 5.3.3. 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.
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 2.
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).
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Figure 2 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.
+-------+ +-------+
| PSAP | (7) | ESRP |
| |<----->| |
+-------+ +-------+
^
| (7)
v
+----------+ (6) +----------+
| Mapping |<----->| ESRP |
| Database | | |<-+
+----------+ +----------+ |
^ |
+------------------------|--------|--------------+
| ISP | | |
|+----------+ | | +----------+|
|| LCS-ISP | | | | DHCP ||
|| |<-----------+ | | Server ||
|+----------+ (4) | +----------+|
+-------^-------------------------|-----------^--+
+-------|-------------------------|-----------|--+
| IAP | (5) | | |
| V | | |
|+----------+ | | |
|| LCS-IAP | +--------+ | | |
|| | | Link | |(3) | |
|+----------+ | Layer | | | |
| | Device | | (2)| |
| +--------+ | | |
| ^ | | |
| | | | |
+------------------------|--------|-----------|--+
| | |
(1)| | |
| | |
| +----+ |
v v |
+----------+ |
| End |<-------------+
| Host |
+----------+
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Figure 2: Architectural Overview
Note: Figure 2 does not indicate who runs the ESRP or the mapping
database. There are different options available.
5.1. End Host Profile
5.1.1. LoST Server Discovery
The end host MAY attempt to use [RFC5222] to discover a LoST server.
If that attempt fails, the end host SHOULD attempt to discover the
address of an ESRP.
5.1.2. 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.
5.1.3. 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 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, but the call would be sent to urn:service:sos. This
mapping SHOULD be performed at the endpoint device.
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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
knows the visited emergency dial strings.
5.1.5. 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.
5.1.6. 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].
5.1.7. Testing
The description in Section 15 of [I-D.ietf-ecrit-phonebcp] is fully
applicable to this document.
5.2. IAP/ISP Profile
5.2.1. 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].
5.2.2. Location Determination and Location Configuration
When receiving an INVITE message the following steps are done:
1. If the INVITE message does not include location information the
ESRP-registrar MUST use HELD identity
[I-D.ietf-geopriv-held-identity-extensions] to obtain the
location of the device as both a location value and reference.
In order to contact the LIS the ESRP-registrar SHOULD determine
the LIS address using the mechanism described in
[I-D.thomson-geopriv-res-gw-lis-discovery]. The ESRP-registrar
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MAY use other methods for LIS determination where available.
2. If the INVITE message contains a location URI then the ESRP-
registrar MUST dereference it so that it has a location available
to route the impending emergency call. The ESRP-registrar MAY
validate the LIS address in the location URI with that of the LIS
serving the network from which the INVITE message originated.
3. The INVITE message contains location information by value. Any
actions performed by the ESRP-registrar to valid this information
are specific to the jurisdiction in which the ESRP operates and
are out of the scope of this document.
5.3. ESRP Profile
5.3.1. 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 [RFC5222] is a
suitable mechanism.
5.3.2. 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.
5.3.3. 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 5.1.5. Furthermore, the ESRP MUST be able to add a reference
to location information, as described in SIP Location Conveyance
[I-D.ietf-sipcore-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.
5.3.4. Location Retrieval
The ESRP acts a location recipient and the usage of HELD [RFC5985]
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.
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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.
6. Lower Layer Considerations for NAA Case
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.
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
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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.
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:
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2.
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 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.
3. 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 Method 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
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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
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
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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. 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
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.
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
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 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 returned to IP addresses and hope that the resolution captures
all possible DNS responses.) Since the media destination addresses
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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.
Finally, a number of security vulnerabilities discussed in
[I-D.ietf-geopriv-arch] around faked location information are less
problematic in the context of unauthenticated emergency 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.
8. Acknowledgments
Parts of this document are derived from [I-D.ietf-ecrit-phonebcp].
Participants of the 2nd and 3rd SDO Emergency Services Workshop
provided helpful input.
9. IANA Considerations
This document does not require actions by IANA.
10. References
10.1. Normative References
[I-D.ietf-sipcore-location-conveyance]
Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
for the Session Initiation Protocol",
draft-ietf-sipcore-location-conveyance-03 (work in
progress), July 2010.
[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.
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[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.
[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.
10.2. Informative References
[RFC5687] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
Location Configuration Protocol: Problem Statement and
Requirements", RFC 5687, March 2010.
[I-D.ietf-ecrit-framework]
Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
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"Framework for Emergency Calling using Internet
Multimedia", draft-ietf-ecrit-framework-11 (work in
progress), July 2010.
[I-D.thomson-geopriv-res-gw-lis-discovery]
Thomson, M. and R. Bellis, "Location Information Server
(LIS) Discovery using IP address and Reverse DNS",
draft-thomson-geopriv-res-gw-lis-discovery-04 (work in
progress), September 2010.
[RFC5985] Barnes, M., "HTTP-Enabled Location Delivery (HELD)",
RFC 5985, September 2010.
[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-05 (work in
progress), October 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-03 (work in progress),
October 2010.
[esw07] "3rd SDO Emergency Services Workshop,
http://www.emergency-services-coordination.info/2007Nov/",
October 30th - November 1st 2007.
[nwgstg3] "WiMAX Forum WMF-T33-001-R015V01, WiMAX Network
Architecture Stage-3
http://www.wimaxforum.org/sites/wimaxforum.org/files/ tech
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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
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
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Dirk Kroeselberg
Nokia Siemens Networks
St.-Martin-Str. 76
Munich 81541
Germany
Phone: +49 (89) 515933019
Email: Dirk.Kroeselberg@nsn.com
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