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Internet Engineering Task Force (IETF) H. Schulzrinne
Request for Comments: 7406 Columbia University
Category: Informational S. McCann
ISSN: 2070-1721 BlackBerry Ltd
G. Bajko
MediaTek
H. Tschofenig
D. Kroeselberg
Siemens Corporate Technology
December 2014
Extensions to the Emergency Services Architecture for Dealing With
Unauthenticated and Unauthorized Devices
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 document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7406.
Schulzrinne, et al. Informational [Page 1]
RFC 7406 Unauthenticated Emergency Service December 2014
Copyright Notice
Copyright (c) 2014 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Use-Case Categories . . . . . . . . . . . . . . . . . . . . . 5
4. ZBP Considerations . . . . . . . . . . . . . . . . . . . . . 12
5. NASP Considerations . . . . . . . . . . . . . . . . . . . . . 12
5.1. End-Host Profile . . . . . . . . . . . . . . . . . . . . 15
5.1.1. LoST Server Discovery . . . . . . . . . . . . . . . . 15
5.1.2. ESRP Discovery . . . . . . . . . . . . . . . . . . . 15
5.1.3. Location Determination and Location Configuration . . 15
5.1.4. Emergency Call Identification . . . . . . . . . . . . 15
5.1.5. SIP Emergency Call Signaling . . . . . . . . . . . . 15
5.1.6. Media . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1.7. Testing . . . . . . . . . . . . . . . . . . . . . . . 16
5.2. IAP/ISP Profile . . . . . . . . . . . . . . . . . . . . . 16
5.2.1. ESRP Discovery . . . . . . . . . . . . . . . . . . . 16
5.2.2. Location Determination and Location Configuration . . 16
5.3. ESRP Profile . . . . . . . . . . . . . . . . . . . . . . 16
5.3.1. Emergency Call Routing . . . . . . . . . . . . . . . 16
5.3.2. Emergency Call Identification . . . . . . . . . . . . 16
5.3.3. SIP Emergency Call Signaling . . . . . . . . . . . . 17
6. Lower-Layer Considerations for NAA Case . . . . . . . . . . . 17
6.1. Link-Layer Emergency Indication . . . . . . . . . . . . . 18
6.2. Securing Network Attachment in NAA Cases . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Normative References . . . . . . . . . . . . . . . . . . 21
8.2. Informative References . . . . . . . . . . . . . . . . . 22
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
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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 telephony 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; those
devices are not traditional telephones, and users are increasingly
expecting them to be able 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 (Internet Access Provider
(IAP) or 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 the
Public Safety Answering Point (PSAP) URI by offering Location-to-
Service Translation (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.
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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 No ASP (NASP) and
zero-balance ASP (ZBP) cases below, 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.
No ASP (NASP): The caller does not have an ASP at the time of the
call. This can occur in case the caller either does not possess
any valid subscription for a reachable ASP or does possess a valid
subscription but none of the ASPs are 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 a 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 both in an 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 Voice Service Providers (VSPs), it is
technically possible to let a caller place an emergency call in the
ZBP case. We discuss each case in more detail in Section 3.
Some of the functionality provided in this document is already
available in the Public Switched Telephone Network (PSTN).
Consequently, there is real-world experience available and not all of
it is positive. For example, the functionality of calls without
Subscriber Identity Modules (SIMs) in today's cellular system has
lead to a fair amount of hoax or test calls in certain countries.
Schulzrinne, et al. Informational [Page 4]
RFC 7406 Unauthenticated Emergency Service December 2014
This causes overload situations at PSAPs, which is considered harmful
to the overall availability and reliability of emergency services.
As an example, the 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
Standards Development Organization (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 [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
An end host needs to perform the following steps if it is not
attached to the network and the user is starting to place an
emergency call:
Link-Layer Attachment: Some networks have added support for
unauthenticated emergency access while others have advertised
these capabilities using layer beacons (multicast or broadcast
announcements). The end host learns about these unauthenticated
emergency services capabilities from either the link layer type or
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.
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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 the need for help, a user dials an
emergency number and the SIP User Agent (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 earlier.
+-----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
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RFC 7406 Unauthenticated Emergency Service December 2014
+------------+ | +------------+ +------------+
| 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|
`...../ `...../
Abbreviations:
LLA: Link-Layer Attachment
ES: Emergency Services
Figure 1: Flow Diagram: NAA, ZBP, and NSAP Scenarios
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RFC 7406 Unauthenticated Emergency Service December 2014
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
+------------+
| Execute |
| NAA |
| Procedures |
+------------+
Schulzrinne, et al. Informational [Page 8]
RFC 7406 Unauthenticated Emergency Service December 2014
|
| 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
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RFC 7406 Unauthenticated Emergency Service December 2014
+------------+ +---------+
| ASP | NO | See |
| Configured?|----->| main |
+------------+ | diagram |
| `........./
|
| YES
|
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
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RFC 7406 Unauthenticated Emergency Service December 2014
+-----+
+------------|Start|-----------------+
| `...../ |
v v
+------------+ +----------------+
| NAA | | Regular |
| Procedures | | Network Access |
+------------+ | Procedures |
| +----------------+
| |
| |
----------------o--------------------+
|
|
|
|
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
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RFC 7406 Unauthenticated Emergency Service December 2014
The NAA procedures are described in Section 6. The ZBP procedures
are described in Section 4. The NASP procedures are described in
Section 5. The Phone BCP procedures are described in [RFC6881]. The
LLA procedures are not described in this document since they are
specific to the link-layer technology in use.
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 some 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,
preconfigured 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 attach 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).
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o When the end host has configured the IP address, it starts an
interaction with the discovered LCS at the ISP, as shown in step
(3). In certain deployments, the ISP may 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 is
shown in step (5).
o In step (6), the SIP UA initiates a SIP INVITE request 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 step (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 brevity, 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 Sections 6.5 and 6.6
of [RFC6881] regarding the interaction between the device and the
Location Information Server (LIS) applies to this document.
The SIP UA in the end host MUST attach available location information
in a Presence Information Data Format Location Object (PIDF-LO)
[RFC4119] when making an emergency call. When constructing the
PIDF-LO, the guidelines in the 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 dial string 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 of [RFC6881].
To enable callbacks, SIP UAs SHOULD place a globally routable URI in
a Contact header field.
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5.1.6. Media
Endpoints MUST comply with the media requirements for endpoints
placing an emergency call as described 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 endpoints 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 Sections 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
proprietary, but the description in [LIS] 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
while others have advertised 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 or 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 signaled in the IEEE 802.16-2009 wireless
link. In IEEE 802.11 WLAN [IEEE802.11], an emergency support
indicator allows the station (i.e., end host in this context) to
download before association to a Network Access Identifier (NAI),
which it can use to request server-side authentication only for an
IEEE 802.1X network.
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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 EAP
[RFC3748] is of particular relevance here. Examples are the EAP
NAI decoration used in Worldwide Interoperability for Microwave
Access (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 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 protocol layers and entities involved. 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
authentication, authorization, and policy decision process.
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
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early stages of link-layer activity in the network attachment
process. Possible conflicts may arise, e.g., in case of filtering
based on Media Access Control (MAC) in entities terminating link-
layer signaling in the network (like a base station). In normal
operation, EAP-related information will only be recognized in the
Network Access Server (NAS). Any entity residing between the 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 access based
on IEEE 802.11 or IEEE 802.16. 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 a Master Session Key
(MSK) to the authenticator to bootstrap further key derivation for
protecting the wireless link).
To match the above, the following approaches 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 IEEE 802.1X network. The
details are incorporated in the IEEE 802.11-2012 specification
[IEEE802.11].
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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 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 is 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 network attachment
based on EAP-TLS with client authentication based on the device
certificate.
7. Security Considerations
The security threats discussed in [RFC5069] are applicable to this
document.
The NASP and NAA cases introduce new vulnerabilities since the PSAP
operator will typically not have any information about the identity
of the caller via the signaling path. Today, in countries where this
functionality is used for Global System for Mobile Communications
(GSM) networks, 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. However, the details, e.g., for using filtering,
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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 an unauthenticated emergency when
location information can be verified by the ISP to fall within a
specific geographical area.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[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, <http://www.rfc-editor.org/info/rfc3261>.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005,
<http://www.rfc-editor.org/info/rfc4119>.
[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services", RFC 5031,
January 2008, <http://www.rfc-editor.org/info/rfc5031>.
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[RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location
Format for Presence Information Data Format Location
Object (PIDF-LO)", RFC 5139, February 2008,
<http://www.rfc-editor.org/info/rfc5139>.
[RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, August 2008,
<http://www.rfc-editor.org/info/rfc5222>.
[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, <http://www.rfc-editor.org/info/rfc5223>.
[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,
<http://www.rfc-editor.org/info/rfc5491>.
[RFC6881] Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in Support of Emergency Calling",
BCP 181, RFC 6881, March 2013,
<http://www.rfc-editor.org/info/rfc6881>.
8.2. Informative References
[IEEE802.11]
IEEE, "IEEE Standard for Information Technology -
Telecommunications and information exchange between
systems - Local and metropolitan area networks - Specific
requirements Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) Specifications", IEEE Std
802.11-2012, March 2012,
<http://standards.ieee.org/about/get/802/802.11.html>.
[LIS] Winterbottom, J. and S. Norreys, "LIS to LIS Protocol
Requirements", Work in Progress, draft-winterbottom-
geopriv-lis2lis-req-01, November 2007.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004, <http://www.rfc-editor.org/info/rfc3748>.
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RFC 7406 Unauthenticated Emergency Service December 2014
[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for
Emergency Context Resolution with Internet Technologies",
RFC 5012, January 2008,
<http://www.rfc-editor.org/info/rfc5012>.
[RFC5069] Taylor, T., Tschofenig, H., Schulzrinne, H., and M.
Shanmugam, "Security Threats and Requirements for
Emergency Call Marking and Mapping", RFC 5069, January
2008, <http://www.rfc-editor.org/info/rfc5069>.
[RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
Authentication Protocol", RFC 5216, March 2008,
<http://www.rfc-editor.org/info/rfc5216>.
[RFC5687] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
Location Configuration Protocol: Problem Statement and
Requirements", RFC 5687, March 2010,
<http://www.rfc-editor.org/info/rfc5687>.
[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,
<http://www.rfc-editor.org/info/rfc6280>.
[RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
"Framework for Emergency Calling Using Internet
Multimedia", RFC 6443, December 2011,
<http://www.rfc-editor.org/info/rfc6443>.
[RFC6444] Schulzrinne, H., Liess, L., Tschofenig, H., Stark, B., and
A. Kuett, "Location Hiding: Problem Statement and
Requirements", RFC 6444, January 2012,
<http://www.rfc-editor.org/info/rfc6444>.
[esw07] "3rd Standards Development Organziations (SDO) Emergency
Services Workshop", October 30th - November 1st 2007,
<http://www.emergency-services-
coordination.info/2007Nov/>.
[nwgstg3] WiMAX Forum, "WiMAX Forum Network Architecture - Detailed
Protocols and Procedures Base Specification", Stage-3 WMF-
T33-001-R022V02, April 2014, <http://resources.wimaxforum.
org/sites/wimaxforum.org/files/technical_document/2014/05/
WMF-T33-001-R022v02_Network-Stage3-Base.pdf>.
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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, Marc Linsner, James Polk,
Brian Rosen, and Martin Thomson for their feedback at the IETF#80
Emergency Context Resolution with Internet Technology (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.
Various IESG members provided review comments, including Spencer
Dawkins, Stephen Farrell, Joel Jaeggli, Barry Leiba, Ted Lemon, and
Pete Resnick.
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Authors' Addresses
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
United States
Phone: +1 212 939 7004
EMail: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu
Stephen McCann
BlackBerry Ltd
200 Bath Road
Slough, Berks SL1 3XE
United Kingdom
Phone: +44 1753 667099
EMail: smccann@blackberry.com
URI: http://www.blackberry.com
Gabor Bajko
MediaTek
EMail: gabor.bajko@mediatek.com
Hannes Tschofenig
Hall in Tirol 6060
Austria
EMail: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Dirk Kroeselberg
Siemens Corporate Technology
Otto-Hahn-Ring 6
Munich 81739
Germany
EMail: dirk.kroeselberg@siemens.com
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