ECRIT                                                     H. Schulzrinne
Internet-Draft                                       Columbia University
Intended status: Standards Track                               S. McCann
Expires: April 28, September 30, 2011                    Research in Motion UK Ltd
                                                                G. Bajko
                                                                   Nokia
                                                           H. Tschofenig
                                                          D. Kroeselberg
                                                  Nokia Siemens Networks
                                                        October 25, 2010
                                                          D. Kroeselberg
                                                                 Siemens
                                                          March 29, 2011

   Extensions to the Emergency Services Architecture for dealing with
                Unauthenticated and Unauthorized Devices
             draft-ietf-ecrit-unauthenticated-access-01.txt
             draft-ietf-ecrit-unauthenticated-access-02.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
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 28, September 30, 2011.

Copyright Notice

   Copyright (c) 2010 2011 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 . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6  7
   3.  Use Case Categories  . . . . . . . . . . . . . . . . . . . . .  6  8
   4.  ZBP Considerations . . . . . . . . . . . . . . . . . . . . . .  8 10
   5.  NASP Considerations  . . . . . . . . . . . . . . . . . . . . .  9 11
     5.1.  End Host Profile . . . . . . . . . . . . . . . . . . . . . 11 13
       5.1.1.  LoST Server Discovery  . . . . . . . . . . . . . . . . 11 13
       5.1.2.  ESRP Discovery . . . . . . . . . . . . . . . . . . . . 11 13
       5.1.3.  Location Determination and Location Configuration  . . 11 13
       5.1.4.  Emergency Call Identification  . . . . . . . . . . . . 11 13
       5.1.5.  SIP Emergency Call Signaling . . . . . . . . . . . . . 12 13
       5.1.6.  Media  . . . . . . . . . . . . . . . . . . . . . . . . 12 14
       5.1.7.  Testing  . . . . . . . . . . . . . . . . . . . . . . . 12 14
     5.2.  IAP/ISP Profile  . . . . . . . . . . . . . . . . . . . . . 12 14
       5.2.1.  ESRP Discovery . . . . . . . . . . . . . . . . . . . . 12 14
       5.2.2.  Location Determination and Location Configuration  . . 12 14
     5.3.  ESRP Profile . . . . . . . . . . . . . . . . . . . . . . . 13 14
       5.3.1.  Emergency Call Routing . . . . . . . . . . . . . . . . 13 14
       5.3.2.  Emergency Call Identification  . . . . . . . . . . . . 13 14
       5.3.3.  SIP Emergency Call Signaling . . . . . . . . . . . . . 13
       5.3.4.  Location Retrieval . . . . . . . . . . . . . . . . . . 13 15
   6.  Lower Layer Considerations for NAA Case  . . . . . . . . . . . 14 16
     6.1.  Link Layer Emergency Indication  . . . . . . . . . . . . . 14 16
     6.2.  Higher-Layer Emergency Indication  . . . . . . . . . . . . 15
     6.3.  Securing Network Attachment in NAA Cases . . . . . . . . . 17
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18 20
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 19 21
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19 22
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 23
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 19 23
     10.2. Informative References . . . . . . . . . . . . . . . . . . 20 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22 26

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
      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
   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. ISP.  The end host
      uses a Location Configuration Protocol (LCP) to retrieve location
      information.  Subsequently, the LoST protocol [RFC5222] is used to
      learn the relevant emergency numbers, and to obtain the PSAP URI
      applicable for that location.

   Emergency Call:  In case of need for help, a user dials an emergency
      number and the SIP UA initiates the emergency call procedures by
      communicating with the PSAP.

   Figure 1 compiles the basic logic taking place during network entry
   for requesting an emergency service and shows the interrelation
   between the three conditions described in the above section.

                         +-----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    |
                    | 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
   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 end host
      starts an interaction with the discovered Location Configuration
      Server at the ISP, as shown in step (3).  The ISP may in certain
      deployments need to interact with the IAP.  This protocol exchange
      is shown in step (4).

   o  Once location information is obtained the end host triggers the
      LoST protocol to obtain the address of the ESRP/PSAP.  This step
      is shown in (5).

   o  In step (6), the SIP UA initiates a SIP INVITE towards the
      indicated ESRP, as shown in
      (3). 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.  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). (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 emergency caller. SIP UA.

   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).

   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) (8)
                                      |
               +----------+(7) +----------+
               | Mapping  |<----->| LoST     |<-->| ESRP     |
               | Database Server   |    |          |          |<-+
               +----------+    +----------+  |
                     ^        |
     +------------------------|--------|--------------+                ^
    +----------------+----------------|--------------+
    | ISP            |                |              |
    |+----------+    |                |  +----------+|
    || LCS-ISP  |            | (3)|                |  | DHCP     ||
    ||          |<-----------+          |<-+ |                |  | Server   ||
    |+----------+     (4)  | |                |  +----------+|
     +-------^-------------------------|-----------^--+
     +-------|-------------------------|-----------|--+
    +-------^------+-+----------------|-----------^--+
    +-------|------+-+----------------|-----------|--+
    | IAP   | (5) (4)  | |(5)             |           |  |
    |       V      | |                |           |  |
    |+----------+  | |                |           |  |
    || LCS-IAP  |  | |  +--------+    |           |  |
    ||          |  | |  | Link   |    |(3)    |(6)        |  |
    |+----------+  | |  | Layer  |    |           |  |
    |              | |  | Device |    |        (2)|  |
    |              | |  +--------+    |           |  |
    |              | |       ^        |           |  |
    |              | |       |        |
     +------------------------|--------|-----------|--+           |  |
    +--------------+-|-------|--------|-----------|--+
                   | |       |        |           |
                   | |    (1)|        |           |
                   | |       |        |           |
                   | |       |   +----+           |
                   | |       v   v   |                |
                   | |  +----------+              |
                   | +->| End      |<-------------+
                         |
                   +___>| Host     |
                        +----------+

                     Figure 2: Architectural Overview

   Note: Figure 2 does not indicate who runs operates the ESRP or and the mapping
   database.  There are different LoST
   server.  Various deployment options available. exist.

5.1.  End Host Profile

5.1.1.  LoST Server Discovery

   The end host MAY attempt to use [RFC5222] to MUST discover a LoST server.
   If that attempt fails, the end host SHOULD attempt to discover the
   address of an ESRP. server [RFC5222] using DHCP
   [RFC5223].

5.1.2.  ESRP Discovery

   The end host only needs an ESRP when location configuration or LoST
   server discovery fails.  If that is MUST discover the case, then ESRP using the LoST protocol
   [RFC5222].

5.1.3.  Location Determination and Location Configuration

   The end host MUST
   use the "Dynamic Host Configuration Protocol (DHCP-for-IPv4) Option
   for Session Initiation Protocol (SIP) Servers" [RFC3361] (for IPv6) support location acquisition and / or the "Dynamic Host Configuration Protocol (DHCPv6) Options
   for Session Initiation Protocol (SIP) Servers" [RFC3319] to discover the address LCPs described
   in Section 6.5 of an ESRP.  This SIP proxy located [I-D.ietf-ecrit-phonebcp].  The description in
   Section 6.5 and 6.6 of [I-D.ietf-ecrit-phonebcp] regarding 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
   interaction between the internal procedure for emergency call
   processing is subject of ISP internal operation.

5.1.3.  Location Determination device 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 LIS applies to the PSAP. this document.

   The SIP UA in the end host MUST attach available location information
   in a PIDF-LO [RFC4119] when making an emergency call.  When
   constructing the PIDF-LO the guidelines in PIDF-LO profile [RFC5491]
   MUST be followed.  For civic location information the format defined
   in [RFC5139] MUST be supported.

5.1.4.  Emergency Call Identification

   To determine which calls are emergency calls, some entity needs to
   map a user entered dialstring into this URN scheme.  A user may
   "dial" 1-1-2, 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
   knows the visited emergency dial strings. string.

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 SHOULD place 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 provision a DHCP server with information about LoST
   servers [RFC5223].  An ISP operator may choose to deploy a LoST
   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]. to outsource it to other parties.

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

   The ISP is responsible for location determination and exposes this
   information the
       ESRP-registrar MUST use HELD identity
       [I-D.ietf-geopriv-held-identity-extensions] to obtain the end points via location configuration protocols.
   The considerations described in [I-D.ietf-ecrit-location-hiding-req]
   are applicable to this document.

   The ISP MUST support one of the LCPs described in Section 6.5 of
   [I-D.ietf-ecrit-phonebcp].  The description in Section 6.5 and 6.6 of
   [I-D.ietf-ecrit-phonebcp] regarding the interaction between the end
   device as both a location value and reference.
       In order the LIS applies to contact this document.

   The interaction between the LIS at the ESRP-registrar SHOULD determine ISP and the LIS address using IAB is often
   priorietary but the mechanism described description in
       [I-D.thomson-geopriv-res-gw-lis-discovery].  The ESRP-registrar
       MAY use other methods for LIS determination where available.
   2.  If
   [I-D.winterbottom-geopriv-lis2lis-req] may be relevant to 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. reader.

5.3.  ESRP Profile

5.3.1.  Emergency Call Routing

   The ESRP must continues to 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  This may
   require further interactions with LoST [RFC5222] is a
   suitable mechanism. 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) 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. tree).

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.

   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  In IEEE 802.11 WLAN, an emergency support
      indicator allows the STA to download before association an IEEE 802.1X NAI
      which it can use to occur without
      exchanging cryptogrpahic keys.

   Higher-layer emergency indication:  Typically emergency indication request server side authentication only for an
      802.1x network.

   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.  Examples
      are the EAP NAI decoration used in WiMAX networks and modification
      of the authentication exchange in IEEE 802.11. [nwgstg3].

6.1.  Link Layer Emergency Indication

   In general, link layer emergency indications provide good integration
   into the actual network access procedure regarding the enabling of
   means to recognize and prioritize an emergency service request from
   an end host at a very early stage of the network attachment
   procedure.  However, support in end hosts for such methods cannot be
   considered to be commonly available.

   No general recommendations are given in the scope of this memo due to
   the following reasons:

   o  Dependency on the specific access technology.

   o  Dependency on the specific access network architecture.  Access
      authorization and policy decisions typically happen at a different
      layers of the protocol stack and in different entities than those
      terminating the link-layer signaling.  As a result, link layer
      indications need to be distributed and translated between the
      different involved protocol layers and entities.  Appropriate
      methods are specific to the actual architecture of the IAP/ISP
      network.

6.2.  Higher-Layer Emergency Indication

   This section focuses on emergency indications based on authentication
   and authorization in EAP-based network access.

   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 link-layer indications into the AA 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
      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:

   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, entities terminating the
          absence of a client certificate could be interpreted by link-layer signaling in the
      network as (like a request for emergency network attachment.

       2.c) Emergency EAP Method:

          A new base station).  In normal operation, EAP method could related
      information will only be defined that is specifically
          designed for emergency network entry recognized in NAA cases.  Most
          likely, such EAP method would the NAS.  Any entity
      residing between end host and NAS should not be usable for standard
          emergency network attachment with an existing subscription.
          Such dedicated emergency expected to
      understand/parse EAP method should messages.

   o  An emergency indication can be key-generating
          in compliance with RFC3748 to enable given by forming a specific NAI
      that is used as the regular air interface
          security methods even identity in unauthenticated operation.

6.3. EAP based authentication for
      network entry.

6.2.  Securing Network Attachment in NAA Cases

   For network attachment in NAA cases, it may make sense to secure the
   link-layer connection between the device and the IAP/ISP.  This
   especially holds for wireless access with examples being IEEE 802.11
   or IEEE 802.16 based access.  The latter even mandates secured
   communication across the wireless link for all IAP/ISP networks based
   on [nwgstg3].

   Therefore, for network attachment that is by default based on EAP
   authentication it is desirable also for NAA network attachment to use
   a key-generating EAP method (that provides an MSK key to the
   authenticator to bootstrap further key derivation for protecting the
   wireless link).

   The following approaches to match the above can be identified:

   1) Server-only Authentication:

      The device of the emergency service requester performs an EAP
      method with the IAP/ISP EAP server that performs server side
      authentication only.  An example for this is EAP-TLS.  This
      provides a certain level of assurance about the IAP/ISP to the
      device user.  It requires the device to be provisioned with
      appropriate trusted root certificates to be able to verify the
      server certificate of the EAP server (unless this step is
      explicitly skipped in the device in case of an emergency service
      request).  This method is used to provide access of devices
      without existing credentials to an 802.1x network.  The details
      are incorporated into the not yet published 802.11-2011
      specification.

   2) Null Authentication:

      In one case (e.g.  WiMAX) an EAP method is performed.  However, no
      credentials specific to either the server or the device or
      subscription are used as part of the authentication exchange.  An
      example for this would be an EAP-TLS exchange with using the
      TLS_DH_anon (anonymous) ciphersuite.  Alternatively, a publicly
      available static key for emergency access could be used.  In the
      latter case, the device would need to be provisioned with the
      appropriate emergency key for the IAP/ISP in advance.  In another
      case (e.g.  IEEE 802.11), no EAP method is used, so that empty
      frames are transported during the over the air IEEE 802.1X
      exchange.  In this case the authentication state machine completes
      with no cryptographic keys being exchanged.

   3) Device Authentication:

      This case extends the server-only authentication case.  If the
      device is configured with a device certificate and the IAP/ISP EAP
      server can rely on a trusted root allowing the EAP server to
      verify the device certificate, at least the device identity (e.g.,
      the MAC address) can be authenticated by the IAP/ISP in NAA cases.
      An example for this are WiMAX devices that are shipped with device
      certificates issued under the global WiMAX device public-key
      infrastructure.  To perform unauthenticated emergency calls, if
      allowed by the IAP/ISP, such devices perform EAP-TLS based network
      attachment with client authentication based on the device
      certificate.

7.  Security Considerations

   The security threats discussed in [RFC5069] are applicable to this
   document.

   There are a couple of new vulnerabilities raised with unauthenticated
   emergency services in NASP/NAA cases since the PSAP operator will
   typically not possess any identity information about the emergency
   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
   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.

   We would like to thank Richard Barnes, Brian Rosen, James Polk, Marc
   Linsner, and Martin Thomson for their feedback at the IETF#80 ECRIT
   meeting.

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.

   [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
              draft-ietf-ecrit-phonebcp-17 (work in progress),
              July 2010.
              March 2011.

   [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,
              "Framework for Emergency Calling using Internet
              Multimedia", draft-ietf-ecrit-framework-11 draft-ietf-ecrit-framework-12 (work in
              progress), July October 2010.

   [I-D.thomson-geopriv-res-gw-lis-discovery]

   [I-D.ietf-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
              draft-ietf-geopriv-res-gw-lis-discovery-01 (work in
              progress), September 2010. March 2011.

   [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.,

   [I-D.ietf-ecrit-location-hiding-req]
              Schulzrinne, H., Liess, L., Tschofenig, H., Stark, B., and R.
              Barnes, "Use of Device Identity in HTTP-Enabled Location
              Delivery (HELD)",
              draft-ietf-geopriv-held-identity-extensions-05
              A. Kuett, "Location Hiding: Problem Statement and
              Requirements", draft-ietf-ecrit-location-hiding-req-04
              (work in progress), October February 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
              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
   Dirk Kroeselberg
   Nokia
   Siemens Networks
   St.-Martin-Str. 76
   Munich  81541
   Germany

   Phone: +49 (89) 515933019
   Email: Dirk.Kroeselberg@nsn.com dirk.kroeselberg@siemens.com