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Versions: (draft-schulzrinne-ecrit-unauthenticated-access) 00 01 02 03 04 05 06 07 08 09 10 RFC 7406

ECRIT                                                     H. Schulzrinne
Internet-Draft                                       Columbia University
Intended status: Standards Track                               S. McCann
Expires: February 13, 2015                     Research in Motion UK Ltd
                                                                G. Bajko

                                                           H. Tschofenig

                                                          D. Kroeselberg
                                                                 Siemens
                                                         August 12, 2014


   Extensions to the Emergency Services Architecture for dealing with
                Unauthenticated and Unauthorized Devices
             draft-ietf-ecrit-unauthenticated-access-10.txt

Abstract

   This document provides a problem statement, introduces terminology
   and describes an extension for the base IETF emergency services
   architecture to address cases where an emergency caller is not
   authenticated, has no identifiable service provider, or has no
   remaining credit with which to pay for access to the network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   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 February 13, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Use Case Categories . . . . . . . . . . . . . . . . . . . . .   5
   4.  ZBP Considerations  . . . . . . . . . . . . . . . . . . . . .  11
   5.  NASP Considerations . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  End Host Profile  . . . . . . . . . . . . . . . . . . . .  14
       5.1.1.  LoST Server Discovery . . . . . . . . . . . . . . . .  14
       5.1.2.  ESRP Discovery  . . . . . . . . . . . . . . . . . . .  14
       5.1.3.  Location Determination and Location Configuration . .  14
       5.1.4.  Emergency Call Identification . . . . . . . . . . . .  14
       5.1.5.  SIP Emergency Call Signaling  . . . . . . . . . . . .  14
       5.1.6.  Media . . . . . . . . . . . . . . . . . . . . . . . .  15
       5.1.7.  Testing . . . . . . . . . . . . . . . . . . . . . . .  15
     5.2.  IAP/ISP Profile . . . . . . . . . . . . . . . . . . . . .  15
       5.2.1.  ESRP Discovery  . . . . . . . . . . . . . . . . . . .  15
       5.2.2.  Location Determination and Location Configuration . .  15
     5.3.  ESRP Profile  . . . . . . . . . . . . . . . . . . . . . .  15
       5.3.1.  Emergency Call Routing  . . . . . . . . . . . . . . .  15
       5.3.2.  Emergency Call Identification . . . . . . . . . . . .  15
       5.3.3.  SIP Emergency Call Signaling  . . . . . . . . . . . .  16
   6.  Lower Layer Considerations for NAA Case . . . . . . . . . . .  16
     6.1.  Link Layer Emergency Indication . . . . . . . . . . . . .  17
     6.2.  Securing Network Attachment in NAA Cases  . . . . . . . .  18
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     10.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   Summoning police, the fire department or an ambulance in emergencies
   is one of the fundamental and most-valued functions of the telephone.
   As telephone functionality moves from circuit-switched telephony to



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   Internet telephony, its users rightfully expect that this core
   functionality will continue to work at least as well as it has for
   the older technology.  New devices and services are being made
   available that could be used to make a request for help, those
   devices are not traditional telephones, and users are increasingly
   expecting them to be used to place emergency calls.

   Roughly speaking, the IETF emergency services architecture (see
   [RFC6881] and [RFC6443]) divides responsibility for handling
   emergency calls among the access network (ISP); the application
   service provider (ASP), which may be a VoIP service provider (VSP);
   and the provider of emergency signaling services, the emergency
   service network (ESN).  The access network may provide location
   information to end systems, but does not have to provide any ASP
   signaling functionality.  The emergency caller can reach the ESN
   either directly or through the ASP's outbound proxy.  Any of the
   three parties can provide the mapping from location to PSAP URI by
   offering LoST [RFC5222] services.

   In general, a set of automated configuration mechanisms allows a
   device to function in a variety of architectures, without the user
   being aware of the details on who provides location, mapping services
   or call routing services.  However, if emergency calling is to be
   supported when the calling device lacks access network authorization
   or does not have an ASP, one or more of the providers may need to
   provide additional services and functions.

   In all cases, the end device has to be able to perform a LoST lookup
   and otherwise conduct the emergency call in the same manner as when
   the three exceptional conditions discussed below do not apply.

   We distinguish among three conditions:

   No Access Authentication (NAA):  In the NAA case, the emergency
      caller does not posses valid credentials for the access network.
      This includes the case where the access network allows pay-per-
      use, as is common for wireless hotspots, but there is insufficient
      time to enter credit card details and other registration
      information required for access.  It also covers all cases where
      either no credentials are available at all, or the available
      credentials do not work for the given IAP/ISP.  As a result, the
      NAA case basically combines the below NASP and ZBP cases, but at
      the IAP/ISP level.  Support for emergency call handling in the NAA
      case is subject to the local policy of the ISP.  Such policy may
      vary substantially between ISPs and typically depends on external
      factors that are not under the ISP control.





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   No ASP (NASP):  The caller does not have an ASP at the time of the
      call.  This can occur either in case the caller does not possess
      any valid subscription for a reachable ASP, or in case none of the
      ASPs where the caller owns a valid subscription is reachable
      through the ISP.

      Note: The interoperability need is increased with this scenario
      since the client software used by the emergency caller must be
      compatible with the protocols and extensions deployed by the ESN.


   Zero-balance ASP (ZBP):  In the case of zero-balance ASP, the ASP can
      authenticate the caller, but the caller is not authorized to use
      ASP services, e.g., because the contract has expired or the
      prepaid account for the customer has been depleted.


   These three cases are not mutually exclusive.  A caller in need of
   help may, for example, be in a NAA and NASP situation, as explained
   in more detail in Figure 1.  Depending on local policy and
   regulations, it may not be possible to place emergency calls in the
   NAA case.  Unless local regulations require user identification, it
   should always be possible to place calls in the NASP case, with
   minimal impact on the ISP.  Unless the ESN requires that all calls
   traverse a known set of VSPs, it is technically possible to let a
   caller place an emergency call in the ZBP case.  We discuss each case
   in more details in Section 3.

   As mentioned in the abstract some of the functionality provided in
   this document is already available in the PSTN.  Consequently, there
   is real-world experience available and not all of it is positive.
   For example, the functionality of SIM-less calls in today's cellular
   system has lead to a fair amount of hoax or test calls in certain
   countries.  This causes overload situations at PSAPs, which is
   considered harmful to the overall availability and reliability of
   emergency services.

      As an example, Federal Office of Communications (OFCOM,
      Switzerland) provided statistics about emergency (112) calls in
      Switzerland from Jan.  1997 to Nov. 2001.  Switzerland did not
      offer SIM-less emergency calls except for almost a month in July
      2000 where a significant increase in hoax and test calls was
      reported.  As a consequence, the functionality was disabled again.
      More details can be found in the panel presentations of the 3rd
      SDO Emergency Services Workshop [esw07].






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2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in RFC 2119
   [RFC2119].

   This document reuses terminology from [RFC5687] and [RFC5012], namely
   Internet Access Provider (IAP), Internet Service Provider (ISP),
   Application Service Provider (ASP), Voice Service Provider (VSP),
   Emergency Service Routing Proxy (ESRP), Public Safety Answering Point
   (PSAP), Location Configuration Server (LCS), (emergency) service dial
   string, and (emergency) service identifier.

3.  Use Case Categories

   On a very high-level, the steps to be performed by an end host that
   is not attached to the network and the user starting to make an
   emergency call are the following:

   Link Layer Attachment:  Some networks have added support for
      unauthenticated emergency access, some other type of networks
      advertise these capabilities using layer beacons.  The end host
      learns about these unauthenticated emergency services capabilities
      either from the link layer type or from advertisement.

      The end host uses the link layer specific network attachment
      procedures defined for unauthenticated network access in order to
      get access to the network.


   Pre-Emergency Service Configuration:  When the link layer network
      attachment procedure is completed the end host learns basic
      configuration information using DHCP from the ISP.  The end host
      uses a Location Configuration Protocol (LCP) to retrieve location
      information.  Subsequently, the LoST protocol [RFC5222] is used to
      learn the relevant emergency numbers, and to obtain the PSAP URI
      applicable for that location.


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

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




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                         +-----Y
                         |Start|
                         `...../
                            |
                            | Are credentials
                            | for network attachment
                            | available?
                            |
               NO           v         YES
             +----------------------------+
             |                            |
             |                            |
             V                            v
        ..............               ................
        | Idle: Wait |               |Execute       |
        | for ES Call|               |LLA Procedures|
        | Initiation |               "--------------'
        "------------'                    |
    Is        |               +---------->O
    emergency |               |           | Is ASP
    service   | NO +-----Y    |           | configured?
    network   +--->| End |    |           +---------------+
    attachment|    `...../    |       YES |               | NO
    possible? |               |           |               |
              v               |           v               v
        +------------+        |     +------------+    +------------+
        | Execute    |        |     | Execute    |    | Execute    |
        | NAA        |--------+     | Phone BCP  |    | NASP       |
        | Procedures |              | Procedures |    | Procedures |
        +------------+              +------------+    +------------+
                         Authorization for|                |
                            making an     |                |
                         emergency call   |                |
                         with the ASP/VSP?|                |
                           +--------------+                v
                           | NO           | YES         +-----Y
                           |              |             | Done|
                           v              v             `...../
                    +------------+  +------------+
                    | Execute    |  | Execute    |
                    | ZBP        |  | Phone BCP  |
                    | Procedures |  | Procedures |
                    +------------+  +------------+
                           |              |
                           |              |
                           v              v
                        +-----Y        +-----Y
                        | Done|        | Done|



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                        `...../        `...../

   Abbreviations:
     LLA: Link Layer Attachment
     ES: Emergency Services

           Figure 1: Flow Diagram: NAA, ZBP, and NSAP Scenarios.

   The diagrams below highlight the most important steps for the three
   cases.

               +-----Y
               |Start|
               `...../
                  |
                  | No
                  | credentials
                  | for network access
                  | available
                  v
            ..............
            | Idle: Wait |
            | for ES Call|
            | Initiation |
            "------------'
                  |
                  |
                  |
                  v
                  --
                //  --
               /      --
             //  Is     --
            /  emergency  --
            |   service    |  NO   +--------+
            |   network    |------>| Call   |
            |  attachment  |         Failed |
            \  possible?   /       `......./
             \           //
              \\       //
                \    //
                 \--/
                  |
                  | YES
                  |
                  |
                  v
            +------------+



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            | Execute    |
            | NAA        |
            | Procedures |
            +------------+
                  |
                  | Network
                  | attachment
                  | in progress
                  v
                /--\  Continue
               |    | with
               |    | application
                \--/  layer interaction

                   Figure 2: Flow Diagram: NAA Scenario.

                        +-----+
           +------------|Start|-----------------+
           |            `...../                 |
           v                                    v
     +------------+                     +----------------+
     | NAA        |                     | Regular        |
     | Procedures |                     | Network Access |
     +------------+                     | Procedures     |
           |                            +----------------+
           |                                    |
           |                                    |
           ----------------o--------------------+
                           |
                           |
                           |
                           |
                       Network
                       Attachment
                       Completed
                           |
                           |
                           |
                           |
                           v
                     +------------+      +---------+
                     | ASP        |  NO  | See     |
                     | Configured?|----->| main    |
                     +------------+      | diagram |
                           |             `......../
                           |
                           | YES
                           |



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                           v
                        //----
                       /      --
                     //         --
                    /              -       +---------+
                    | Authorization|  YES  | See     |
                    | for making   |------>| main    |
                    |   ES call    |       | diagram |
                    \    with      /       `......../
                     \  VSP/ASP? //
                      \\       //
                        \    //
                         \--/
                           |
                           | NO
                           |
                           |
                           v
                     +------------+
                     | Execute    |
                     | ZBP        |
                     | Procedures |
                     +------------+
                           |
                           | Call
                           | in progress
                           |
                           v
                       +--------+
                       | Call   |
                         Success|
                       `......./

                   Figure 3: Flow Diagram: ZBP Scenario.

                              +-----+
                 +------------|Start|-----------------+
                 |            `...../                 |
                 v                                    v
           +------------+                     +----------------+
           | NAA        |                     | Regular        |
           | Procedures |                     | Network Access |
           +------------+                     | Procedures     |
                 |                            +----------------+
                 |                                    |
                 |                                    |
                 ----------------o--------------------+
                                 |



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                                 |
                                 |
                                 |
                             Network
                             Attachment
                             Completed
                                 |
                                 |
                                 |
                                 |
                                 v
                           +------------+      +---------+
                           | ASP        |  YES | See     |
                           | Configured?|----->| main    |
                           +------------+      | diagram |
                                 |             `......../
                                 |
                                 | NO
                                 |
                                 v
                           +------------+
                           | Execute    |
                           | NASP       |
                           | Procedures |
                           +------------+
                                 |
                                 | Call
                                 | in progress
                                 |
                                 v
                             +--------+
                             | Call   |
                               Success|
                             `......./

                  Figure 4: Flow Diagram: NASP Scenario.

   The "No Access Authentication (NAA)" procedures are described in
   Section 6.  The "Zero-balance ASP (ZBP)" procedures are described in
   Section 4.  The "No ASP (NASP)" procedures are described in
   Section 5.  The Phone BCP procedures are described in [RFC6881].  The
   "Link Layer Attachment (LLA)" procedures are not described in this
   document since they are specific to the link layer technology in use.








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4.  ZBP Considerations

   ZBP includes all cases where a subscriber is known to an ASP, but
   lacks the necessary authorization to access regular ASP services.
   Example ZBP cases include empty prepaid accounts, barred accounts,
   roaming and mobility restrictions, or any other conditions set by ASP
   policy.

   Local regulation might demand that emergency calls cannot proceed
   without successful service authorization.  In regulatory regimes,
   however, it may be possible to allow emergency calls to continue
   despite authorization failures.  To distinguish an emergency call
   from a regular call an ASP can identify emergency sessions by
   inspecting the service URN [RFC5031] used in call setup.  The ZBP
   case therefore only affects the ASP.

   Permitting a call despite authorization failures could present an
   opportunity for abuse.  The ASP may choose to verify the destination
   of the emergency calls and to only permit calls to certain, pre-
   configured entities (e.g., to local PSAPs).  Section 7 discusses this
   topic in more detail.

   An ASP without a regulatory requirement to authorize emergency calls
   can deny emergency call setup.  Where an ASP does not authorize an
   emergency call, the caller may be able to fall back to NASP
   procedures.

5.  NASP Considerations

   To start the description we consider the sequence of steps that are
   executed in an emergency call based on Figure 5.

   o  As an initial step the devices attaches to the network as shown in
      step (1).  This step is outside the scope of this section.

   o  When the link layer network attachment procedure is completed the
      end host learns basic IP configuration information using DHCP from
      the ISP, as shown in step (2).

   o  When the IP address configuration is completed then the end host
      starts an interaction with the discovered Location Configuration
      Server at the ISP, as shown in step (3).  The ISP may in certain
      deployments need to interact with the IAP.  This protocol exchange
      is shown in step (4).

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



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   o  In step (6), the SIP UA initiates a SIP INVITE towards the
      indicated ESRP.  The INVITE message contains all the necessary
      parameters required by Section 5.1.5.

   o  The ESRP receives the INVITE and processes it according to the
      description in Section 5.3.3.

   o  The ESRP routes the call to the PSAP, as shown in (8), potentially
      interacting with a LoST server first to determine the route.

   o  The PSAP evaluates the initial INVITE and aims to complete the
      call setup.

   o  Finally, when the call setup is completed media traffic can be
      exchanged between the PSAP and the SIP UA.

   For editorial reasons the end-to-end SIP and media exchange between
   the PSAP and SIP UA are not shown in Figure 5.

































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

                     Figure 5: Architectural Overview

   Note: Figure 5 does not indicate who operates the ESRP and the LoST
   server.  Various deployment options exist.






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5.1.  End Host Profile

5.1.1.  LoST Server Discovery

   The end host MUST discover a LoST server [RFC5222] using DHCP
   [RFC5223] unless a LoST server has been provisioned using other
   means.

5.1.2.  ESRP Discovery

   The end host MUST discover the ESRP using the LoST protocol [RFC5222]
   unless a ESRP has been provisioned using other means.

5.1.3.  Location Determination and Location Configuration

   The end host MUST support location acquisition and the LCPs described
   in Section 6.5 of [RFC6881].  The description in Section 6.5 and 6.6
   of [RFC6881] regarding the interaction between the device and the LIS
   applies to this document.

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

5.1.4.  Emergency Call Identification

   To determine which calls are emergency calls, some entity needs to
   map a user entered dialstring into this URN scheme.  A user may
   "dial" 1-1-2, 9-1-1, etc., but the call would be sent to
   urn:service:sos.  This mapping SHOULD be performed at the endpoint
   device.

   End hosts MUST use the Service URN mechanism [RFC5031] to mark calls
   as emergency calls for their home emergency dial string.

5.1.5.  SIP Emergency Call Signaling

   SIP signaling capabilities [RFC3261] are REQUIRED for end hosts.

   The initial SIP signaling method is an INVITE.  The SIP INVITE
   request MUST be constructed according to the requirements in
   Section 9.2 [RFC6881].

   Regarding callback behavior SIP UAs SHOULD place a globally routable
   URI in a Contact: header.




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5.1.6.  Media

   End points MUST comply with the media requirements for end points
   placing an emergency call found in Section 14 of [RFC6881].

5.1.7.  Testing

   The description in Section 15 of [RFC6881] is fully applicable to
   this document.

5.2.  IAP/ISP Profile

5.2.1.  ESRP Discovery

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

5.2.2.  Location Determination and Location Configuration

   The ISP is responsible for location determination and exposes this
   information to the end points via location configuration protocols.
   The considerations described in [RFC6444] are applicable to this
   document.

   The ISP MUST support one of the LCPs described in Section 6.5 of
   [RFC6881].  The description in Section 6.5 and 6.6 of [RFC6881]
   regarding the interaction between the end device and the LIS applies
   to this document.

   The interaction between the LIS at the ISP and the IAP is often
   priorietary but the description in
   [I-D.winterbottom-geopriv-lis2lis-req] may be relevant to the reader.

5.3.  ESRP Profile

5.3.1.  Emergency Call Routing

   The ESRP continues to route the emergency call to the PSAP
   responsible for the physical location of the end host.  This may
   require further interactions with LoST servers but depends on the
   specific deployment.

5.3.2.  Emergency Call Identification

   The ESRP MUST understand the Service URN mechanism [RFC5031] (i.e.,
   the 'urn:service:sos' tree).




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5.3.3.  SIP Emergency Call Signaling

   SIP signaling capabilities [RFC3261] are REQUIRED for the ESRP.  The
   ESRP MUST process the messages sent by the client, according to
   Section 5.1.5.

   Furthermore, if a PSAP wants to support NASP calls, then it MUST NOT
   restrict incoming calls to a particular set of ASPs.

6.  Lower Layer Considerations for NAA Case

   Some networks have added support for unauthenticated emergency
   access, some other type of networks advertise these capabilities
   using layer beacons.  The end host learns about these unauthenticated
   emergency services capabilities either from the link layer type or
   from advertisement.

   It is important to highlight that the NAA case is inherently a layer
   2 problem, and the general form of the solution is to provide an
   "emergency only" access type, with appropriate limits/monitoring to
   prevent abuse.  The described mechanisms are informative in nature
   since the relationship to the IETF emergency services architecture is
   only indirect, namely via some protocols developed within the IETF
   (e.g., EAP and EAP methods) that require extensions to support this
   functionality.

   This section discusses different methods to indicate an emergency
   service request as part of network attachment.  It provides some
   general considerations and recommendations that are not specific to
   the access technology.

   To perform network attachment and get access to the resources
   provided by an IAP/ISP, the end host uses access technology specific
   network attachment procedures, including for example network
   detection and selection, authentication, and authorization.  For
   initial network attachment of an emergency service requester, the
   method of how the emergency indication is given to the IAP/ISP is
   specific to the access technology.  However, a number of general
   approaches can be identified:

   Link layer emergency indication:  The end host provides an
      indication, e.g., an emergency parameter or flag, as part of the
      link layer signaling for initial network attachment.  Examples
      include an emergency bit signalled in the IEEE 802.16-2009
      wireless link.  In IEEE 802.11 WLAN, an emergency support
      indicator allows the station (i.e., end host in this context) to
      download before association a Network Access Identifier (NAI),




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      which it can use to request server side authentication only for an
      802.1x network.


   Higher-layer emergency indication:  Typically, emergency indication
      is provided in the network access authentication procedure.  The
      emergency caller's end host provides an indication as part of the
      access authentication exchanges.  Authentication via the
      Extensible Authentication Protocol (EAP) [RFC3748] is of
      particular relevance here.  Examples are the EAP NAI decoration
      used in WiMAX networks and modification of the authentication
      exchange in IEEE 802.11. [nwgstg3].


6.1.  Link Layer Emergency Indication

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

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

   o  Dependency on the specific access technology.

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

   o  An advantage of combining emergency indications with the actual
      network attachment procedure performing authentication and
      authorization is the fact that the emergency indication can
      directly be taken into account in the authentication and
      authorization server that owns the policy for granting access to
      the network resources.  As a result, there is no direct dependency
      on the access network architecture that otherwise would need to
      take care of merging link-layer indications into the AA and policy
      decision process.





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   o  EAP signaling happens at a relatively early stage of network
      attachment, so it is likely to match most requirements for
      prioritization of emergency signaling.  However, it does not cover
      early stages of link layer activity in the network attachment
      process.  Possible conflicts may arise e.g. in case of MAC-based
      filtering in entities terminating the link-layer signaling in the
      network (like a base station).  In normal operation, EAP related
      information will only be recognized in the NAS.  Any entity
      residing between end host and NAS should not be expected to
      understand/parse EAP messages.

   o  An emergency indication can be given by forming a specific NAI
      that is used as the identity in EAP based authentication for
      network entry.

6.2.  Securing Network Attachment in NAA Cases

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

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

   The following approaches to match the above can be identified:

   1) Server-only Authentication:

      The device of the emergency service requester performs an EAP
      method with the IAP/ISP EAP server that performs server side
      authentication only.  An example for this is EAP-TLS [RFC5216].
      This provides a certain level of assurance about the IAP/ISP to
      the device user.  It requires the device to be provisioned with
      appropriate trusted root certificates to be able to verify the
      server certificate of the EAP server (unless this step is
      explicitly skipped in the device in case of an emergency service
      request).  This method is used to provide access of devices
      without existing credentials to an 802.1x network.  The details
      are incorporated into the not yet published 802.11-2011
      specification.





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   2) Null Authentication:

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


   3) Device Authentication:

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

7.  Security Considerations

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

   There are a couple of new vulnerabilities raised with unauthenticated
   emergency services in NASP/NAA cases since the PSAP operator will
   typically not possess any identity information about the emergency
   caller via the signaling path itself.  In countries where this
   functionality is used for GSM networks today this has lead to a
   significant amount of misuse.

   In the context of NAA, the IAP and the ISP will probably want to make
   sure that the claimed emergency caller indeed performs an emergency
   call rather than using the network for other purposes, and thereby
   acting fraudulent by skipping any authentication, authorization and
   accounting procedures.  By restricting access of the unauthenticated
   emergency caller to the LoST server and the PSAP URI, traffic can be



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   restricted only to emergency calls.  This can be accomplished with
   traffic separation.  The details, however, e.g. for using filtering,
   depend on the deployed ISP architecture and are beyond the scope of
   this document.

   We only illustrate a possible model.  If the ISP runs its own
   (caching) LoST server, the ISP would maintain an access control list
   populated with IP-address information obtained from LoST responses
   (in the mappings).  These URIs would either be URIs for contacting
   further LoST servers or PSAP URIs.  It may be necessary to translate
   domain names returned in LoST responses to IP addresses.  Since the
   media destination addresses are not predictable, the ISP also has to
   provide a SIP outbound proxy so that it can determine the media
   addresses and add those to the filter list.

   For the ZBP case the additional aspect of fraud has to be considered.
   Unless the emergency call traverses a PSTN gateway or the ASP charges
   for IP-to-IP calls, there is little potential for fraud.  If the ASP
   also operates the LoST server, the outbound proxy MAY restrict
   outbound calls to the SIP URIs returned by the LoST server.  It is
   NOT RECOMMENDED to rely on a fixed list of SIP URIs, as that list may
   change.

   RFC 6280 [RFC6280] discusses security vulnerabilities that are caused
   by an adversary faking location information and thereby lying about
   the actual location of the emergency caller.  These threats may be
   less problematic in the context of unauthenticated emergency when
   location information can be verified by the ISP to fall within a
   specific geographical area.

8.  Acknowledgments

   Parts of this document are derived from [RFC6881].  Participants of
   the 2nd and 3rd SDO Emergency Services Workshop provided helpful
   input.

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

   Furthermore, we would like to thank Martin Thomson and Bernard Aboba
   for their detailed document review in preparation of the 81st IETF
   meeting.  Alexey Melnikov was the General Area (Gen-Art) reviewer.  A
   number of changes to the document had been made in response to the AD
   review by Richard Barnes.






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   We would also like to thank review comments from various IESG
   members, including Stephen Farrell, Barry Leiba, Pete Resnick,
   Spencer Dawkins, Joel Jaeggli, and Ted Lemon.

9.  IANA Considerations

   This document does not require actions by IANA.

10.  References

10.1.  Normative References

   [RFC5031]  Schulzrinne, H., "A Uniform Resource Name (URN) for
              Emergency and Other Well-Known Services", RFC 5031,
              January 2008.

   [RFC4119]  Peterson, J., "A Presence-based GEOPRIV Location Object
              Format", RFC 4119, December 2005.

   [RFC5491]  Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
              Presence Information Data Format Location Object (PIDF-LO)
              Usage Clarification, Considerations, and Recommendations",
              RFC 5491, March 2009.

   [RFC5139]  Thomson, M. and J. Winterbottom, "Revised Civic Location
              Format for Presence Information Data Format Location
              Object (PIDF-LO)", RFC 5139, February 2008.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6881]  Rosen, B. and J. Polk, "Best Current Practice for
              Communications Services in Support of Emergency Calling",
              BCP 181, RFC 6881, March 2013.

   [RFC5222]  Hardie, T., Newton, A., Schulzrinne, H., and H.
              Tschofenig, "LoST: A Location-to-Service Translation
              Protocol", RFC 5222, August 2008.

   [RFC5223]  Schulzrinne, H., Polk, J., and H. Tschofenig, "Discovering
              Location-to-Service Translation (LoST) Servers Using the
              Dynamic Host Configuration Protocol (DHCP)", RFC 5223,
              August 2008.



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10.2.  Informative References

   [RFC5687]  Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
              Location Configuration Protocol: Problem Statement and
              Requirements", RFC 5687, March 2010.

   [RFC6443]  Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
              "Framework for Emergency Calling Using Internet
              Multimedia", RFC 6443, December 2011.

   [RFC5012]  Schulzrinne, H. and R. Marshall, "Requirements for
              Emergency Context Resolution with Internet Technologies",
              RFC 5012, January 2008.

   [RFC6444]  Schulzrinne, H., Liess, L., Tschofenig, H., Stark, B., and
              A. Kuett, "Location Hiding: Problem Statement and
              Requirements", RFC 6444, January 2012.

   [I-D.winterbottom-geopriv-lis2lis-req]
              Winterbottom, J. and S. Norreys, "LIS to LIS Protocol
              Requirements", draft-winterbottom-geopriv-lis2lis-req-01
              (work in progress), November 2007.

   [RFC5069]  Taylor, T., Tschofenig, H., Schulzrinne, H., and M.
              Shanmugam, "Security Threats and Requirements for
              Emergency Call Marking and Mapping", RFC 5069, January
              2008.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
              3748, June 2004.

   [RFC5216]  Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
              Authentication Protocol", RFC 5216, March 2008.

   [RFC6280]  Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
              Tschofenig, H., and H. Schulzrinne, "An Architecture for
              Location and Location Privacy in Internet Applications",
              BCP 160, RFC 6280, July 2011.

   [esw07]    "3rd SDO Emergency Services Workshop,
              http://www.emergency-services-coordination.info/2007Nov/",
              October 30th - November 1st 2007.








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   [nwgstg3]  "WiMAX Forum WMF-T33-001-R015V01, WiMAX Network
              Architecture Stage-3
              http://www.wimaxforum.org/sites/wimaxforum.org/files/
              technical_document/2009/09/DRAFT-T33-001-R015v01-
              O_Network-Stage3-Base.pdf", September 2009.

Authors' Addresses

   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   450 Computer Science Building
   New York, NY  10027
   US

   Phone: +1 212 939 7004
   Email: hgs+ecrit@cs.columbia.edu
   URI:   http://www.cs.columbia.edu


   Stephen McCann
   Research in Motion UK Ltd
   200 Bath Road
   Slough, Berks  SL1 3XE
   UK

   Phone: +44 1753 667099
   Email: smccann@rim.com
   URI:   http://www.rim.com


   Gabor Bajko

   Email: gaborbajko@gmail.com


   Hannes Tschofenig
   Hall in Tirol  6060
   Austria

   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at









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   Dirk Kroeselberg
   Siemens
   Germany

   Email: dirk.kroeselberg@siemens.com














































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