ecrit                                                     H. Schulzrinne
Internet-Draft                                               Columbia U.
Expires: March 6, 2006                                  R. Marshall, Ed.
                                                       September 2, 2005

Requirements for Emergency Context Resolution with Internet Technologies

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Copyright Notice

   Copyright (C) The Internet Society (2005).


   This document enumerates requirements for emergency calls placed by
   the public using voice-over-IP (VoIP) and general Internet multimedia
   systems, where Internet protocols are used end-to-end.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  High-Level Requirements  . . . . . . . . . . . . . . . . . . . 10
   5.  Identifying the Caller Location  . . . . . . . . . . . . . . . 12
   6.  Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 13
   7.  Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 15
   8.  Emergency Caller  Identification . . . . . . . . . . . . . . . 19
   9.  Performance and Reliability Considerations . . . . . . . . . . 20
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 23
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     13.1.  Normative References  . . . . . . . . . . . . . . . . . . 24
     13.2.  Informative References  . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
   Intellectual Property and Copyright Statements . . . . . . . . . . 26

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1.  Introduction

   Users of voice-centric, (telephone-like) IP-based services expect to
   be able to call for emergency help, such as police, the fire
   department, or ambulance services, regardless of where they are, what
   (if any) service provider they are using, or what type of device they

   Additionally, users of other real-time and near real-time services
   (those other than voice) also expect to be able to summon emergency
   help.  For example, instant messaging (IM) and real time text users
   want to have access to the same types of emergency services as
   mentioned above.  IM and real time text are particularly helpful for
   hearing-disabled users, (RFC 3351 [4]), when there is a need for
   exactness as for example for spelling out names and addresses and in
   cases where bandwidth is scarce.

   Unfortunately, the mechanisms for emergency calls that have evolved
   in the public circuit-switched telephone network (PSTN) are not quite
   appropriate for evolving IP-based voice, text and real-time
   multimedia communications.  This document outlines the key
   requirements that end systems and network elements such as SIP
   proxies need to satisfy in order to provide emergency call services
   which at a minimum, offer the same functionality as existing PSTN
   services, with the goal of making emergency calling more robust,
   less-costly to implement, and multimedia-capable.

   This document only focuses on end-to-end IP-based calls, i.e., where
   the emergency call originates from an IP end system, (Internet
   device), and terminates to an IP-capable PSAP, done entirely over an
   IP network.

   This document outlines the various functional issues which relate to
   making an IP-based emergency call, including a description of general
   requirements, (Section 4), identification of the emergency caller's
   location, (Section 5), use of an emergency identifier to declare a
   call to be an emergency call, (Section 6), the mapping function
   required to route the call to the appropriate PSAP, (Section 7), and
   finally, identifying who placed the call, (Section 8)

   Note that location is required for two separate purposes, first, to
   route the call to the appropriate PSAP and second, to display the
   caller's location to the call taker for help in dispatching emergency
   assistance to the correct location.

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2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
   indicate requirement levels for compliant implementations.

   Since a requirements document does not directly specify a protocol to
   implement, these compliance labels should be read as indicating
   requirements for the protocol or architecture, rather than an

   For lack of a better term, we will use the term "caller" or
   "emergency caller" to refer to the person placing an emergency call
   or sending an emergency IM.

   Access Infrastructure Provider (AIP): An organization that provides
      physical network connectivity to its customers or users, e.g.
      through digital subscriber lines, cable TV plants, Ethernet,
      leased lines or radio frequencies.  This entity may or may not
      also provide IP routing, IP addresses, or other Internet protocol
      services.  Examples of such organizations include
      telecommunication carriers, municipal utilities, larger
      enterprises with their own network infrastructure, and government
      organizations such as the military.

   address: A description of a location of a person, organization, or
      building, most often consisting of numerical and text elements
      such as street number, street name, and city arranged in a
      particular format.

   Application Service (Voice) Provider (ASP, VSP): The organization
      that provides voice or other application-layer services, such as
      call routing, a SIP URI or PSTN termination.  This organization
      can be a private individual, an enterprise, a government or a
      service provider.  We avoid the term voice service provider, since
      emergency calls are sometimes likely to use other media, including
      text and video.  For a particular user, the ASP may not be the
      same organization as the AIP or ISP.

   Basic Emergency Service: Basic Emergency Service allows a user to
      reach a PSAP serving its current location, but the PSAP may not be
      able to determine the identity or geographic location of the
      caller (except by having the call taker ask the caller).

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   call taker: A call taker is an agent at the PSAP that accepts calls
      and may dispatch emergency help.  (Sometimes the functions of call
      taking and dispatching are handled by different groups of people,
      but these divisions of labor are not generally visible to the
      outside and thus do not concern us here.)

   civic location: A described location based on some defined grid, such
      as a jurisdictional, postal, metropolitan, or rural reference
      system (e.g. street address).

   emergency address: The sip:uri, sips:uri, or tel:uri which represents
      the network address of the PSAP useful for the completion of a
      VoIP emergency call.

   emergency caller: The user or user device entity which sends his/her
      location to another entity in the network.

   emergency identifier: The numerical and/or text identifier which is
      supplied by a user or a user device, which identifies the call as
      an emergency call and is translated into an emergency address for
      call routing and completion.

   enhanced emergency service: Enhanced emergency services add the
      ability to identify the caller identity and/or caller location to
      basic emergency services.  (Sometimes, only the caller location
      may be known, e.g. from a public access point that is not owned by
      an individual.)

   ESRP (Emergency Services Routing Proxy): An ESRP is a call routing
      entity that invokes the location-to-URL mapping, which in turn may
      return either the URL for another ESRP or the PSAP.  (In a SIP
      system, the ESRP would typically be a SIP proxy, but could also be
      a Back-to-back user agent (B2BUA).

   geographic location: A reference to a locatable point described by a
      set of defined coordinates within a geographic coordinate system,
      (e.g. lat/lon within WGS-84 datum)

   Internet Service Provider (ISP): An organization that provides IP
      network-layer services to its customers or users.  This entity may
      or may not provide the physical-layer and layer-2 connectivity,
      such as fiber or Ethernet.

   location: A geographic identification assigned to a region or feature
      based on a specific coordinate system, or by other precise
      information such as a street address.  In the geocoding process,
      the location is defined with an x,y coordinate value according to
      the distance north or south of the equator and east or west of the

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      prime meridian.

   location validation: A caller location is considered valid if the
      civic or geographic location is recognizable within an acceptable
      location reference systems (e.g.  USPS, WGS84, etc.), and can be
      mapped to one or more PSAPs.  Location validation ensures that a
      location is reference able, but makes no assumption about the
      association between the caller and the caller's location.

   Mapping: Process of resolving an address to a URI (or multiple URIs).

   Mapping Client: A Mapping Client interacts with the Mapping Server to
      learn one or multiple URIs for a given address.

   Mapping Server: The Mapping Server holds information about the
      address to URI mappings.

   Miniumum Connectivity: A minimum set of [physical, virtual...??]
      connectivity between two endpoints.

      [Ed.  Send additional text.]

   PSAP (Public Safety Answering Point): Physical location where
      emergency calls are received under the responsibility of a public
      authority.  (This terminology is used by both ETSI, in ETSI SR 002
      180, and NENA.)  In the United Kingdom, PSAPs are called Operator
      Assistance Centres, in New Zealand, Communications Centres.
      Within this document, it is assumed, unless stated otherwise, that
      PSAP is that which supports the receipt of emergency calls over
      IP.  It is also assumed that the PSAP is reachable by IP-based
      protocols, such as SIP for call signaling and RTP for media.

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3.  Basic Actors

   In order to support emergency services covering a large physical area
   various infrastructure elements are necessary: Access Infrastructure
   Providers, Application (Voice) Service Provider, PSAPs as endpoints
   for emergency calls, directory services or other infrastructure
   elements that assist in during the call routing and potentially many
   other entities.

   This section outlines which entities will be considered in the
   routing scenarios discussed.

      Information     +-----------------+
          |(1)        |Access           |   +-----------+
          v           |Infrastructure   |   |           |
     +-----------+    |Provider         |   | Directory |
     |           |    | (3)             |   |           |
     | Emergency |<---+-----------------+-->|           |
     | Caller    |    | (2)             |   +-----------+
     |           |<---+-------+         |          ^
     +-----------+    |  +----|---------+------+   |
          ^           |  |   Location   |      |   |
          |           |  |   Information<-+    |   |
          |           +--+--------------+ |(8) |   | (5)
          |              |    +-----------v+   |   |
          |   (4)        |    |Emergency   |   |   |
          +--------------+--->|Call Routing|<--+---+
          |              |    |Support     |   |
          |              |    +------------+   |
          |              |       ^             |
          |              |   (6) |        +----+--+
          |    (7)       |       +------->|       |
          +--------------+--------------->| PSAP  |
                         |                |       |
                         |Application     +----+--+
                         |(Voice)              |
                         |Service              |
                         |Provider             |

   Figure 1: Framework

   Figure 1 shows the interaction between the entities involved in the
   call.  There are a number of different deployment choices, as it can
   be easily seen from the figure.  The following deployment choices
   need to be highlighted:

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   o How is location information provided to the end host?  It might
   either be known to the end host itself (due to manual configuration
   or provided via GPS) or available via a third party.  Even if
   location information is known to the network it might be made
   available to the end host.  Alternatively, location information is
   used as part of call routing and inserted by intermediaries.

   o Is the Access Infrastructure Provider also the Application (Voice)
   Service Provider?  In the Internet today these roles are typically
   provided by different entities.  As a consequence, the Application
   (Voice) Service Provider is typically not able to learn the physical
   location of the Emergency Caller.

   Please note that the overlapping squares aim to indicate that certain
   functionality can be collapsed into a single entity.  As an example,
   the Application (Voice) Service Provider might be the same entity as
   the Access Infrastructure Provider and they might also operate the
   PSAP.  There is, however, no requirement that this must be the case.
   Additionally it is worth pointing out that end systems might be its
   own VSP, e.g., for enterprises or residential users.

   Below, we describe various interactions between the entities shown in
   Figure 1 are described:

   o (1) Location information might be available to the end host itself.

   o (2) Location information might, however, also be obtained from the
   Access Infrastructure Provider (e.g., using DHCP or application layer
   signaling protocols).

   o (3) The Emergency Caller might need to consult a directory to
   determine the PSAP that is appropriate for the physical location of
   the emergency caller (and considering other attributes such as a
   certain language support by the Emergency Call Takers).

   o (4) The Emergency Caller might get assistance for emergency call
   routing by infrastructure elements (referred as Emergency Call
   Routing Support entities).  In case of SIP these entities are

   o (5) Individual Emergency Call Routing Support entities might need
   to consult a directory to determine where to route the emergency

   o (6) The Emergency Call Routing Support entities need to finally
   forward the call, if infrastructure based emergency call routing is

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   o (7) The emergency caller might interact directly with the PSAP
   without any Emergency Call Routing Support entities.

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4.  High-Level Requirements

   Below, we summarize high-level architectural requirements that guide
   some of the component requirements detailed later in the document.

   R1.  Application Service Provider:  The existence of an Application
      Service Provider (ASP) MUST NOT be assumed.

      Motivation: The caller may not have a application (voice) service
      provider.  For example, a residence may have its own DNS domain
      and run its own SIP proxy server for that domain.  On a larger
      scale, a university might provide voice services to its students
      and staff, but not be a telecommunication provider.

   R2.  International:  The protocols and protocol extensions developed
      MUST support regional, political and organizational differences.

      Motivation: It must be possible for a device or software developed
      or purchased in one country to place emergency calls in another
      country.  System components should not be biased towards a
      particular set of emergency numbers or languages.  Also, different
      countries have evolved different ways of organizing emergency
      services, e.g. either centralizing them or having smaller regional
      subdivisions such as United States counties or municipalities
      handle emergency calls.

   R3.  Distributed Administration:  Deployment of emergency services
      MUST NOT depend on a sole central administration authority.

      Motivation: Once common standards are established, it must be
      possible to deploy and administer emergency calling features on a
      regional or national basis without requiring coordination with
      other regions or nations.  The system cannot assume, for example,
      that there is a single global entity issuing certificates for
      PSAPs, ASPs, AIPs or other participants.

   R4.  Multiple Modes:  Multiple communication modes, such as audio,
      video and text messaging MUST be supported.

      Motivation: In PSTN, voice and text telephony (often called TTY or
      textphone in North America ) are the only commonly supported
      media.  Emergency calling must support a variety of media.  Such
      media should include voice, conversational text (RFC 4103 [6]),
      instant messaging and video.

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   R5.  Minimum Connectivity:  An emergency call SHOULD succeed as long
      as there is a working network path between the caller and the
      PSAP.  In particular, reliance during call set-up and calls on
      entities and network paths that are located elsewhere should be

      Example: A caller in New York who needs to contact a PSAP in the
      same city shouldn't have to get information from some entity in
      Texas to make that call, as the call would then fail if the New
      York to Texas path is unavailable.  (To avoid this, the caller
      could, for example, have cached mapping information, use a local
      server that has the necessary information, or use other mechanisms
      to avoid such off-path dependencies.)

      [Ed.  Added a skeleton definintion of "minimum connectivity" to
      terms section (per ietf63 ecrit meeting minutes note), but still
      no resolution for the above.]

   R6.  Incremental Deployment:  The ECRIT mapping protocol MUST return
      URIs that are useable by a standard signaling protocol (i.e.,
      without special emergency extensions) unless an error is returned.

      Motivation: The format of the output returned by the mapping
      protocol is in a standard format for communication protocol.  For
      example, it should return something SIP specific (e.g.  URI), that
      any SIP capable phone would be able to use if used in a SIP
      context.  Special purpose URIs would not be understood by "legacy"
      SIP devices since they do not have knowledge about the mapping
      protocol, and therefore are not to be used.

   R7.  Relay Services:  It SHOULD be possible to involve relay services
      in the call for translation between different modes.

      Motivation: It should be possible to connect the relay service so
      that the direct flow of media to the emergency service is
      maintained.  In addition, it should be possible to convey
      telemetry data, such as data from automobile crash sensors.

   D1.  PSAP Identification:  The mapping information MUST be available
      without having to enroll with a service provider.

      Motivation: The mapping server may well be operated by a service
      provider, but access to the server offering the mapping must not
      require use of a specific ISP or VSP.

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5.  Identifying the Caller Location

   Location can either be provided directly, or by reference, and
   represents either a civic location, or as a geographic location.  How
   does the location (or location reference) become associated with the
   call?  In general, we can distinguish three modes of operation of how
   a location is associated with an emergency call:

   UA-inserted: The caller's user agent inserts the location
      information, derived from sources such as GPS, DHCP or link-layer
      announcements (LLDP).

   UA-referenced: The caller's user agent provides a reference, via a
      permanent or temporary identifier, to the location which is stored
      by a location service somewhere else and then retrieved by the

   Proxy-inserted: A proxy along the call path inserts the location or
      location reference.

   L6.  Validation of civic location: It MUST be possible to validate an
      address prior to its use in an actual emergency call.

      Motivation: Location validation refers to a process to determine
      whether or not a given civic location is valid or not.

   L10.  Preferred datum: The preferred coordinate reference system for
      emergency calls MUST be WGS-84.

   L28.  Location Provided: An Emergency Services Routing Proxy (ESRP)
      MUST NOT remove location information after performing location
      based routing.

      Motivation: The ESRP and the PSAP use the same location
      information object but for a different purpose.  Therefore, the
      PSAP still requires the receipt of information which represents
      the end device's location.

   L29.: Validation of civic addresses MUST NOT be required to enable
      any feature that is part of the emergency call process.

      Motivation: Emergency routing protocols must take into account
      location based on a variety of forms and formats, (e.g. civic
      address, MSAG, USPS, lat/lon, etc.) and be able to perform
      adequate PSAP routing for the context in which the call is

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6.  Emergency Identifier

   A1a.  Universal Identifier - Setup: One or more universal emergency
      identifiers MUST be recognized by any device or network element
      for call setup purposes

      Motivation: There must be some way for any device or element to
      recognize an emergency call throughout the call setup.  This is
      regardless of the device location, the application (voice) service
      provider used (if any at all), or of any other factor.  Examples
      of these might include: 911, 112, and sos.*.

   A1b.  Universal Identifier - Mapping: One or more universal emergency
      identifiers MUST be recognized by any device or network element to
      support mapping.

      Motivation: Mapping must be made to work under all circumstances,
      by any network element or device.  This is regardless of the
      device location, the application (voice) service provider used (if
      any at all), or of any other factor.  Examples of these might
      include: 911, 112, and sos.*.

   A1c.  Emergency Marking: Emergency requests which are not already
      marked as emergency calls, MUST be recognizable and marked by user
      agents, proxies, and other network elements as emergency calls.

      Motivation: SIP and other call signaling protocols are not
      specific to one country or service provider and devices are likely
      to be used across national or service provider boundaries.  Since
      services such as disabling mandatory authentication for emergency
      calls requires the cooperation of outbound proxies, the outbound
      proxy has to be able to recognize the emergency address and be
      assured that it will be routed as an emergency call.  A universal
      address also makes it possible to create user interface elements
      that are correctly configured without user intervention.  UA
      features could be made to work without such an identifier, but the
      user interface would then have to provide an unambiguous way to
      declare a particular call an emergency call.

   A3.  Recognizable: Emergency calls MUST be recognizable by user
      agents, proxies and other network elements.

      Motivation: To prevent fraud, an address identified as an
      emergency number for call features or authentication override MUST
      also cause routing to a PSAP.

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   A4.  Minimal configuration: Any local emergency identifiers SHOULD be
      configured automatically, without user intervention.

      Motivation: A new UA "unofficially imported" into an organization
      from elsewhere should have the same emergency capabilities as one
      officially installed.

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7.  Mapping Protocol

   There are two approaches for triggering the mapping protocol: caller-
   based, or mediated.

   From the previous section, we take the requirement of a single (or a
   small number of) emergency addresses which are independent of the
   caller's location.  However, since for reasons of robustness,
   jurisdictional and local knowledge, and since PSAPs only serve a
   limited geographic region, having the call reach the appropriate PSAP
   is crucial.

   There appears to be two basic architectures for translating an
   emergency identifier into the appropriate PSAP emergency address.  We
   refer to these as caller-based and mediated.  In caller-based
   resolution, the caller's user agent consults a directory and
   determines the appropriate PSAP based on its location.

   For mediated resolution, a call signaling server, such as a SIP
   (outbound) proxy or redirect server performs this function.  Note
   that the latter case includes the architecture where the call is
   effectively routed to a copy of the database, rather than having some
   non-SIP protocol query the database.  Since servers may be used as
   outbound proxy servers by clients that are not in the same geographic
   area as the proxy server, any proxy server has to be able to
   translate any caller location to the appropriate PSAP.  (A traveler
   may, for example, accidentally or intentionally configure its home
   proxy server as its outbound proxy server, even while far away from

   The resolution may take place well before the actual emergency call
   is placed, or at the time of the call.

   The problem at hand is more difficult to resolve than that for
   traditional web or email services.  In this case, the emergency
   caller only dialed an emergency identifier, and depending on the
   location, any one of several thousand PSAPs around the world could be
   appropriate PSAP.  In addition, the caller probably does not care
   which specific PSAP answers the call, but rather that it be an
   accredited PSAP, e.g. one run by the local government authorities.
   (Many PSAPs are run by private entities.  For example, universities
   and corporations with large campuses often have their own emergency
   response centers.)

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   I1.  Appropriate PSAP: Calls MUST be routed to the PSAP responsible
      for this particular geographic area.

      Motivation: In particular, the location determination should not
      be fooled by the location of IP telephony gateways or dial-in
      lines into a corporate LAN (and dispatch emergency help to the
      gateway or campus, rather than the caller), multi-site LANs and
      similar arrangements.

   I3.  Mapping redirection: The mapping protocol MUST support
      redirection functionality.

      Motivation: In some cases, an initial mapping may provide a single
      URL for a large geographic area.  The ESRP identified by that URL
      then re-invokes the mapping protocol on a different database to
      obtain another URL for an ESRP or PSAP covering a smaller area.

   D5.  Minimal additional delay: The execution of the mapping protocol
      SHOULD minimize the amount of additional delay to the overall
      call-setup time.

      Motivation: Since outbound proxies will likely be asked to resolve
      the same geographic coordinates repeatedly, a suitable time-
      limited caching mechanism should be supported.

   D7.  Referral: The mapping client MUST be able to contact any server
      and be referred to another server that is more qualified to answer
      the query.

      Motivation: This requirement alleviates the potential for
      incorrect configurations to cause calls to fail, particularly for
      caller-based queries.

   I4.  Return multiple PSAPs: The mapping protocol MUST be able to
      return multiple URLs for different PSAPs that cover the same area.

      The mapping protocol must provide additional information that
      allows the querying entity to determine relevant properties of the

      Motivation: In some cases, the same geographic area is served by
      several PSAPs, for example, a corporate campus might be served by
      both a corporate security department and the municipal PSAP.  The
      mapping protocol should then return URLs for both, with
      information allowing the querying entity to choose one or the
      other.  This determination could be made by either an ESRP, based
      on local policy, or by direct user choice, in the case of caller-
      based trigger methods.

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   I7.  Traceable resolution: The entity requesting mapping SHOULD be
      able to determine the entity or entities who provided the
      emergency address resolution information.

   I8.  Resilience against server failure: A client MUST be able to fail
      over to another replica of the mapping server, so that a failure
      of a server does not endanger the ability to perform the mapping.

   I10.  Incrementally deployable: The mapping function MUST be capable
      of being deployed incrementally.

      It must not be necessary, for example, to have a global street
      level database before deploying the system.  It is acceptable to
      have some misrouting of calls when the database does not (yet)
      contain accurate boundary information.

   I13.  Verify mapping support: The mapping protocol SHOULD support the
      ability for a requesting entity to verify that mapping services
      are available for a referenced location.

      Motivation: It should be possible to make sure ahead of time, that
      requests for emergency services will work when needed.

   I25.  Mapping requested from anywhere: The mapping protocol MUST be
      able to provide the mapping regardless of where the mapping client
      is located, either geographically or by network location.

      Motivation: The mapping client, (such as the ESRP), may not
      necessarily be anywhere close to the caller or the appropriate
      PSAP, but must still be able to obtain a mapping.

   I31: The mapping protocol MUST allow a response to carry multiple

      Motivation: In response to a mapping request, a server will
      normally provide a URI or set of URIs for contacting the
      appropriate PSAP.

   I31b: The mapping protocol MUST be able to return a URI or contact
      method explicitly marked as an alternate contact.

      Motivation: In response to a mapping request, if an expected URI
      is unable to be returned, then mapping server may return an
      alternate URI.  When and how this would be used will be described
      in an operational document.

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   I39.  Location Updates: It SHOULD be possible to have updates of

      Motivation: Updated location information may change call routing,
      (some device measurement techniques provide quick (i.e. early),
      but imprecise "first fix" location).

   I40.  The mapping protocol MUST be extensible to allow for the
      inclusion of new location fields.

      Motivation: This is needed, for example, to accommodate future
      extensions to location information that might be included in the
      PIDF-LO (I-D.ietf-geopriv-pidf-lo-03 [2])

   I41.  Split responsibility: The mapping protocol MUST allow that
      within a single level of the civic address hierarchy, multiple
      mapping servers handle subsets of the data elements.

      Motivation: For example, two directories for the same city or
      county may handle different streets within that city or county.

   I42.  The mapping function MUST be able to be invoked at any time,
      including while an emergency call is in process.

   D9.  Baseline query protocol: A mandatory-to-implement protocol MUST
      be specified.

      Motivation: An over-abundance of similarly-capable choices appears
      undesirable for interoperability.

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8.  Emergency Caller  Identification


      [Ed.  This section was never here, but was requested (H.
      Schulzrinne, 8/09/05 email.).]

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9.  Performance and Reliability Considerations

   Baseline performance and reliability requirements, while tend to be
   more of an implementation related set of issues, should still be
   discussed some within the context of basic requirements for the
   protocol.  Therefore, some suggested values relating to portions of
   the routing protocol are provided.

   Latency to ring-tone It is recommended that a session setup interval
      be no more than 2 seconds, 68% (1-sigma) of the time, 4 seconds
      for 95% (2-sigma), and 8 seconds for 99% (3-sigma), for the
      interval of time between when the session is initiated, until the
      time that the signaling "ring-tone" is received by the initiator.

      [Ed.  Not sure if the inclusion of this here is warranted.  May
      still be controversial.]

   Latency to operator It is recommended that a session setup interval
      be no more than 6 seconds, 68% (1-sigma) of the time, 8 seconds
      for 95% (2-sigma), and 10 seconds for 99% (3-sigma), for the
      interval of time between when the session is initiated, until the
      time that the signaling is received by the operator.

      [Ed. same comment as above.]

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10.  Security Considerations

   Note: Security Considerations are referenced in the ECRIT security
   document [3].

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11.  Contributors

   The information contained in this document is a result of a joint
   effort based on individual contributions by those involved in the
   ECRIT WG.  The contributors include Nadine Abbott, Hideki Arai,
   Martin Dawson, Motoharu Kawanishi, Brian Rosen, Richard Stastny,
   Martin Thomson, James Winterbottom.

   The contributors can be reached at:

   Nadine Abbott

   Hideki Arai  

   Martin Dawson

   Motoharu Kawanishi

   Brian Rosen  

   Richard Stastny

   Martin Thomson

   James Winterbottom

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12.  Acknowledgments

   We would like to thank James Polk, Ted Hardie and Andrew Newton for
   their input.

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13.  References

13.1.  Normative References

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

   [2]  Peterson, J., "A Presence-based GEOPRIV Location Object Format",
        draft-ietf-geopriv-pidf-lo-03 (work in progress),
        September 2004.

   [3]  Tschofenig, H., "Security Threats and Requirements for Emergency
        Calling", draft-tschofenig-ecrit-security-threats-01 (work in
        progress), July 2005.

13.2.  Informative References

   [4]  Charlton, N., Gasson, M., Gybels, G., Spanner, M., and A. van
        Wijk, "User Requirements for the Session Initiation Protocol
        (SIP) in Support of Deaf, Hard of Hearing and Speech-impaired
        Individuals", RFC 3351, August 2002.

   [5]  Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
        Polk, "Geopriv Requirements", RFC 3693, February 2004.

   [6]  Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation",
        RFC 4103, June 2005.

   [7]  Wijk, A., "Framework of requirements for real-time text
        conversation using SIP", draft-ietf-sipping-toip-02 (work in
        progress), August 2005.

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Authors' Addresses

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

   Phone: +1 212 939 7004

   Roger Marshall (editor)
   TeleCommunication Systems
   2401 Elliott Avenue
   2nd Floor
   Seattle, WA  98121

   Phone: +1 206 792 2424

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