ECRIT                                                     H. Schulzrinne
Internet-Draft                                               Columbia U.
Expires: September 7, 2006                              R. Marshall, Ed.
                                                           March 6, 2006

      Requirements for Emergency Context  Resolution with Internet

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Copyright Notice

   Copyright (C) The Internet Society (2006).


   This document enumerates requirements for the context resolution of
   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  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  High-Level Requirements  . . . . . . . . . . . . . . . . . . . 12
   5.  Identifying the Caller's Location  . . . . . . . . . . . . . . 14
   6.  Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 15
   7.  Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 18
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 25
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 26
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     11.1.  Normative References  . . . . . . . . . . . . . . . . . . 27
     11.2.  Informative References  . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
   Intellectual Property and Copyright Statements . . . . . . . . . . 29

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1.  Introduction

   Users of both voice-centric (telephone-like) and non voice type
   services (e.g., text communication for hearing disabled users (RFC
   3351 [8]) have an expectation to be able to initiate a request for
   help in case of an emergency.

   Unfortunately, the existing mechanisms to support emergency calls
   that have evolved within the public circuit-switched telephone
   network (PSTN) are not appropriate to handle evolving IP-based voice,
   text and real-time multimedia communications.  This document outlines
   the key requirements that IP-based 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 additional overall goal of making
   emergency calling more robust, less costly to implement, and

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

   This document outlines the various functional issues which relate to
   placing an IP-based emergency call, including a description of
   baseline 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), and finally, the
   mapping function required to route the call to the appropriate PSAP
   (Section 7).

   Ideally, the mapping protocol would yield a URI from a preferred set
   of URIs (e.g., SIP:URI, SIPS:URI) which would allow an emergency call
   to be completed using IP end-to-end.  Despite this goal, some PSAPs
   may not immediately have IP based connectivity, and therefore it is
   imperative that the URI scheme not be fixed, in order to ensure
   support for a less preferred set of URIs, such as a TEL URI which may
   be used to complete a call via the PSTN.

   Identification of the caller, while not incompatible with the
   requirements for messaging outlined within this document, is
   considered to be outside the scope of the ECRIT charter.

   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.

   As used in this document, validation of location does not require to

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   ascertain whether the location actually exists.  For example,
   validation might only check that the house number in a civic address
   falls within the assigned range, not whether that building exists at
   that spot.  However, such higher precision validation is desirable.

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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].

   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

   Codes: "caller" or "emergency caller" refers to the person placing an
   emergency call or sending an emergency instant message (IM).

   Application Service Provider (ASP): The organization or entity that
      provides application-layer services, which may include voice (see
      "Voice Service Provider").  This entity can be a private
      individual, an enterprise, a government, or a service provider.
      An ASP is more general than a Voice Service Provider, since
      emergency calls may use other media beyond voice, including text
      and video.  For a particular user, the ASP may or may not be the
      same organization as his IAP 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.

   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 URI (e.g., SIP:URI, SIPS:URI, XMPP:URI, IM:
      URI, etc.) which represents the address of the PSAP useful for the
      completion of an emergency call.

   Emergency call routing support: An intermediary function which
      assists in the routing of an emergency call via IP.  An ESRP, is
      an example of an Emergency call routing support entity.

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   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.  A universal emergency identifier is an example
      of an emergency identifier.

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

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

   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 the WGS-84 datum).  For example, (2-D)
      geographic location is defined as an x,y coordinate value pair
      according to the distance North or South of the equator and East
      or West of the prime meridian.

   Home emergency dial string: A home emergency dial string represents a
      (e.g., dialed) sequence of digits, that is used to initiate an
      emergency call within a geographically correct location of a
      caller if it is considered to be a user's "home" location or

   Internet Attachment Provider (IAP): An organization that provides
      physical and layer 2 network connectivity to its customers or
      users, e.g., through digital subscriber lines, cable TV plants,
      Ethernet, leased lines or radio frequencies.  Examples of such
      organizations include telecommunication carriers, municipal
      utilities, larger enterprises with their own network
      infrastructure, and government organizations such as the military.

   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, i.e., it may or may not be the role of
      an IAP.

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   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 number and name.  It can be either a
      civic or geographic location.

   Location-dependent emergency dial string: Location-dependent
      emergency dial strings should be thought of as the digit sequence
      that is dialed in order to reach emergency services.  There are
      two dial strings, namely either a "home emergency dial string", or
      a "visited emergency dial string", and is something separate from
      a universal emergency identifier, since each represents specific
      emergency dial string key sequences which are recognized within a
      local geographic area or jurisdiction.

   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, WGS-84, etc.), and can be
      mapped to one or more PSAPs.  While it is desirable to determine
      that a location exists, validation may not ensure that such a
      location exists.  Location validation ensures that a location is
      able to be referenced for mapping, but makes no assumption about
      the association between the caller and the caller's location.

   Mapping: Process of resolving a location to a URI (or multiple URIs)
      which identify a PSAP, or intermediary which knows about a PSAP
      that is designated as responsible to serve that location.

   Mapping client: A mapping client interacts with the Mapping Server to
      learn one or more URIs for a given location.

   Mapping protocol: A protocol used to convey the mapping request and

   Mapping server: The Mapping Server holds information about the
      location-to-URI mappings.

   Mapping service: A network service which uses a distributed mapping
      protocol, to perform a mapping between a location and a PSAP, or
      intermediary which knows about the PSAP, and is used to assist in
      routing an emergency call.

   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

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      IP.  It is also assumed that the PSAP is reachable by IP-based
      protocols, such as SIP for call signaling and RTP for media.

   PSAP URI: PSAP URI is a general term, used to refer to the output of
      the mapping protocol, and represents either the actual PSAP IP
      address, or the IP address of some other intermediary, e.g., an
      ESRP, which points to the actual PSAP.

   Universal emergency identifier: An emergency identifier which is
      recognized by any compatible endpoint, from any geographic
      location.  A general approach to using universal emergency
      identifiers is outlined in the service URN draft (I-D.ietf-ecrit-
      service-urn [5]).

   Visited emergency dial string: A visited emergency dial string
      represents a sequence of digits that is used to initiate an
      emergency call within a geographically correct location of the
      caller if outside the caller's "home" location or vicinity.

   Voice Service Provider (VSP): A specific type of Application Service
      Provider which provides voice related services based on IP, such
      as call routing, a SIP URI, or PSTN termination.

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3.  Basic Actors

   In order to support emergency services covering a large physical
   area, various infrastructure elements are necessary, including:
   Internet Attachment Providers (IAPs), Application/Voice Service
   Providers (ASPs or VSPs), PSAPs as endpoints for emergency calls,
   mapping services or other infrastructure elements that assist during
   the call routing.

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

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

   Figure 1: Framework for emergency call routing

   Figure 1 shows the interaction between the entities involved in the
   call.  There are a number of different deployment choices, as can be
   easily seen from the figure.

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   o How is location information provided to the end host?  It might
   either be known to the end host itself via manual configuration,
   provided via GPS, or obtained via a third party method.  Even if
   location information is known to the network it might be made
   available to the end host via DHCP (RFC 3825 [2]) or some other
   mechanism.  Alternatively, location information is used as part of
   call routing and inserted by intermediaries.

   o Is the Internet Attachment 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.

   The overlapping squares in the figure indicate that some functions
   can be collapsed into a single entity.  As an example, the
   Application/Voice Service Provider might be the same entity as the
   Internet Attachment Provider.  There is, however, no requirement that
   this must be the case.  Additionally, we consider that end systems
   might act as their own VSP, e.g., either for enterprises or for
   residential users.

   Various potential interactions between the entities depicted in
   Figure 1, are described in the following:

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

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

   (3) The emergency caller might need to consult a mapping service to
   determine the PSAP that is appropriate for the physical location of
   the emergency caller, possibly considering other attributes such as
   appropriate language support by the emergency call taker.

   (4) The emergency caller might get assistance for emergency call
   routing by infrastructure elements that are Emergency Call Routing
   Support entities, e.g., an Emergency Service Routing Proxy (ESRP), in

   (5) Location Information is used by emergency call routing entities
   to determine the appropriate PSAP.

   (6) Individual emergency call routing support entities might need to
   consult a mapping service to determine where to route the emergency

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   (7) For infrastructure-based emergency call routing (in contrast to
   UE-based emergency call routing), the emergency call routing support
   entity needs to forward the call to the PSAP.

   (8) The emergency caller (UE) may interact directly with the PSAP
   (e.g., UE invokes mapping, and initiates a connection), without
   relying on any intermediary 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.

   Re1.  Application/Voice service provider: The existence of an
      Application/Voice Service Provider (ASP/VSP) SHOULD NOT be

      Motivation: The caller may not have an 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.

   Re2.  International: Regional, political and organizational aspects
      MUST be considered during the design of protocols and protocol

      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.

   Re3.  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, IAPs or other participants.

   Re4.  Multiple modes: Multiple communication modes, such as audio,
      video and text MUST be supported (i.e., implemented in the
      protocol, though not necessarily used in all calls).

      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 [10]), instant
      messaging and video.

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   Re5.  Alternate mapping sources: The mapping protocol MUST implement
      a mechanism that allows for the retrieval of mapping information
      from different sources.

      Motivation: This provides the possibility of having available
      alternative sources of mapping information when the normal source
      is unavailable or unreachable.

   Re6.  Differences of currency in mapping sources: For alternate
      mapping, differences in currency between mapping data contained
      within mapping sources SHOULD be minimized.

      Motivation: Alternative sources of mapping data may not have been
      created or updated with the same set of information within the
      same timeframe.

   Re7.  Mapping result usability: The ECRIT mapping protocol MUST
      return a URI (or URIs) that are usable within a standard signaling
      protocol (i.e., without special emergency extensions).

      Motivation: For example, a SIP specific URI returned by the
      mapping protocol, needs to be usable within any SIP capable phone
      in a SIP initiated emergency call.  This is in contrast to a
      "special purpose" URI, which may not be recognizable by a legacy
      SIP device.

   Re8.  PSAP accessibility: 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.

   Re9.  No modification of location databases: The mapping protocol
      SHOULD NOT require that data within location databases be
      transformed or modified in any unusual or unreasonable way in
      order for the mapping protocol to use the data.

      Motivation: Databases which contain civic addresses used within
      location servers, may be used for multiple purposes and
      applications beyond emergency service mapping.

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5.  Identifying the Caller's Location

   Location can either be provided direct, 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
      into the call signaling message.  The location information is
      derived from sources such as GPS, DHCP (RFC 3825 [2]) and
      I-D.ietf-geopriv-dhcp-civil [7]) or utilizing the Link Layer
      Discovery Protocol (LLDP) [see IEEE8021AB].

   UA-referenced: The caller's user agent provides a pointer (i.e., a
      location reference), via a permanent or temporary identifier, to
      the location which is stored by a location service somewhere else
      and then retrieved by the PSAP, ESRP, or other authorized service

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

   Lo1.  Reference datum: The mapping server MUST implement support for
      the WGS-84 coordinate reference system and MAY support other
      coordinate reference systems.

   Lo2.  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 needs to receive the caller's location.

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6.  Emergency Identifier

   Id1.  Universal emergency 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.  An example of this might be "urn:service:sos".

   Id2.  Emergency identifier resolution: Where multiple emergency
      identifiers exist, there MUST be a mechanism to differentiate each
      emergency identifier used, based on the specific type of emergency
      help requested.

      Motivation: Some jurisdictions may have multiple types of
      emergency services available, (e.g., fire, police, ambulance), in
      which case, it is important that any one could be selected

   Id3.  Emergency identifier marking: Any device in the signaling path
      that recognizes by some means that the signaling is associated
      with an emergency call MUST add a specific emergency indication,
      if it doesn't already exist, to the signaling before forwarding
      it.  This marking mechanism must be different than QoS marking.

      Motivation: Marking ensures proper handling as an emergency call
      by downstream elements that may not recognize, for example, a
      local variant of a logical emergency address.

   Id4.  Prevention of fraud: A call MUST be routed to a PSAP if it is
      identified as an emergency call.

      Motivation: This prevents use of the emergency call indication to
      gain access to call features or authentication override for non-
      emergency purposes.

   Id5.  Extensibility of emergency identifiers: The list of defined
      emergency identifiers MUST be extensible, and it is not necessary
      to provide mapping for every possible service.

      Motivation: The use of an emergency identifier is locally

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   Id6.  Discovery of emergency dial strings: The protocol MUST support
      a mechanism to discover existing location-dependent emergency dial
      strings, (e.g., "9-1-1", "1-1-2"), which are contextually
      appropriate for the location of the caller.

      Motivation: Users are trained to dial the appropriate emergency
      dial string to reach emergency services.  There needs to be a way
      to figure out what the dial string is within the local environment
      of the caller.

   Id7.  Local emergency dial string translation: An end device (i.e.,
      SIP UA), SHOULD translate home emergency dial strings into
      universal emergency identifiers.  The UA would most likely be pre-
      provisioned with the appropriate information in order to make such
      a translation.

   Id8.  Emergency dial string replacement: For each signaling protocol
      that can be used in an emergency call, reserved universal
      emergency identifiers SHOULD be allowed to replace the original
      emergency dial strings, based on local conventions, regulations,
      or preference (e.g., as in the case of an enterprise).

      Motivation: Any signaling protocol requires the use of some
      identifier to indicate the called party, and the user terminal may
      lack the capability to determine the actual emergency address
      (PSAP URI).  The use of local conventions may be required as a
      transition mechanism.  Note: Such use complicates international
      movement of the user terminal, and evolution to a standardized
      universal emergency identifier or set of identifiers is preferred.

   Id9.  Universal emergency identifier recognition: A universal
      emergency identifier MUST be recognized by any network element
      which supports the mapping protocol.

   Id10.  Emergency identifier not recognized: A call MUST be recognized
      as an emergency call even if the specific emergency service
      requested is not recognized.

      Motivation: In order to have a robust system that supports
      incremental service deployment while still maintaining a fallback

   Id11.  Discovery of visited emergency dial strings: The mapping
      protocol MUST support (i.e., implement, though not necessarily
      use) a mechanism to allow the end device to learn visited
      emergency dial strings.

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      Motivation: Scenarios exist where a user dials a visited emergency
      dial string that is different from the home emergency dial string:
      If a user (i.e., UA operator) visits a foreign country, observes a
      fire truck with 999 on the side, the expectation is one of being
      able to dial that same number to summon a fire truck.  Another use
      case cited is where a tourist collapses, and a "good Samaritan"
      uses the tourist's cell phone to enter a local emergency dial

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7.  Mapping Protocol

   Given the requirement from the previous section, one of having a
   universal emergency identifier that is independent of the caller's
   location, and since each PSAP only serves a limited geographic
   region, and for reasons of jurisdictional and local knowledge, having
   the call reach the appropriate PSAP based on a mapping protocol is

   There are two basic approaches to invoking a mapping service.  We
   refer to these as caller-based and mediated.  In each case, the
   mapping client initiates a request to a mapping server via a mapping
   protocol.  A proposed mapping protocol is outlined in the document
   I-D.hardie-ecrit-lost [6].

   For caller-based resolution, the caller's user agent invokes a
   mapping service to determine the appropriate PSAP based on the
   location provided.  The resolution may take place well before the
   actual emergency call is placed, or at the time of the call.

   For mediated resolution, a call signaling server, such as a SIP
   (outbound) proxy or redirect server invokes the mapping service.

   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 home.)

   Ma1.  Appropriate PSAP: Calls MUST be routed to the PSAP responsible
      for a particular geographic area.  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.

      Motivation: Routing to the wrong PSAP will result in delays in
      handling emergencies as calls are redirected, and result in
      inefficient use of PSAP resources at the initial point of contact.

   Ma2.  Minimal additional delay: The execution of the mapping protocol
      SHOULD minimize the amount of additional delay to the overall
      call-setup time.

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

   Ma3.  Referral: The mapping protocol MUST support (i.e., Implement
      for use), a mechanism for the mapping client to be able to contact
      any mapping 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.

   Ma4.  Multiple response URIs: The mapping protocol response MUST
      support the inclusion of multiple URIs in the response.

   Ma5.  URI alternate contact: The mapping protocol MUST support the
      return of a URI or contact method explicitly marked as an
      alternate contact.

      Motivation: In response to a mapping request, the mapping server
      may return an alternate URI.  Implementation details to be
      described within an operational document.

   Ma6.  URL properties: The mapping protocol MUST support the ability
      to provide additional information that allows the mapping client
      to determine relevant properties of the URL.

      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 methods.

   Ma7.  Traceable resolution: The mapping protocol SHOULD support the
      ability of the mapping client to be able to determine the entity
      or entities which provided the emergency address resolution

      Motivation: It is important for public safety reasons, that there
      is a method to provide operational traceability in case of errors.

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   Ma8.  URI for error reporting: The mapping protocol MUST support
      (i.e., implement for use) a mechanism to return a URI that can be
      used to report a suspected or known error within the mapping

   Ma9.  Resilience against failure: The mapping protocol MUST support
      (i.e., implement for use) a mechanism to enable the mapping client
      to 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.

   Ma10.  Incrementally deployable: The mapping protocol MUST be
      designed in such a way that supports the incremental deployment of
      mapping services.

      Motivation: 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 PSAP service area information.

   Ma11.  Mapping requested from anywhere: The mapping protocol MUST
      support (i.e., implement, though not necessarily use) the ability
      to provide mapping information in response to queries from any
      (earthly) location, regardless of where the mapping client is
      located, either geographically or by network location.

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

   Ma12.  Extensible protocol: The mapping protocol MUST be designed to
      support the extensibility of location data elements, both for new
      and existing fields.

      Motivation: This is needed, for example, to accommodate future
      extensions to location information that might be included in the
      PIDF-LO (RFC 4119 [3]).

   Ma13.  Split responsibility: The mapping protocol MUST support (i.e.,
      implement for use) the division of data subset handling between
      multiple mapping servers within a single level of a civic location

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

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   Ma14.  Any time mapping: The mapping protocol MUST support (i.e.,
      implement for use) the ability of the mapping function to be
      invoked at any time, including while an emergency call is in
      process and before an emergency call.

      Motivation: Used as a fallback mechanism only, if a mapping query
      fails at emergency call time, it may be advantageous to have prior
      knowledge of the PSAP URI.  This prior knowledge would be obtained
      by performing a mapping query at any time prior to an emergency

   Ma15.  Baseline query protocol: A mandatory-to-implement protocol
      MUST be specified.

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

   Ma16.  Multiple PSAP URIs: The mapping protocol MUST support (i.e.,
      implement, though not necessarily use), a method to be able to
      return multiple URIs for different PSAPs that cover the same area.

   Ma17.  Single URI per contact protocol: Though the mapping protocol
      supports the return of multiple URIs, it SHOULD return only one
      URI per contact protocol, so that clients are not required to
      select among different targets for the same contact protocol.

      Motivation: There may be two or more URIs returned when multiple
      contact protocols are available (e.g., SIP and SMS).  The client
      may select among multiple contact protocols based on its
      capabilities, preference settings, or availability.

   Ma18.  Anonymous mapping: The mapping protocol MUST NOT require the
      true identity of the target for which the location information is
      attributed.  Ideally, no identity information is provided via the
      mapping protocol.  Where identity information is provided, it may
      be in the form of an unlinked pseudonym (RFC 3693 [9]).

   Ma19.  Location delivery by-value: The mapping protocol MUST support
      (i.e., implement, though not necessarily use) the delivery of
      location information using a by-value method, though it MAY also
      support de-referencing a URL that references a location object.

      Motivation: The mapping protocol is not required to support the
      ability to de-reference specific location references.

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   Ma20.  Alternate community names: The mapping protocol MUST support
      both the jurisdictional community name and the postal community
      name fields within the PIDF-LO data.

      Motivation: A mapping query must be accepted with either or both
      community name fields, and provide appropriate responses.  If a
      mapping query is made with only one field present, and if the
      database contains both jurisdictional and postal, the mapping
      protocol response should return both.

   Ma21.  Ubiquitous triggering: The mapping protocol MUST implement,
      but not necessarily use, the ability to be invoked at any time,
      from any location, by any client which supports the mapping

      Motivation: While end devices are the typical initiators of
      mapping service requests, it is also expected that other mapping
      clients, such as relays, 3rd party devices, PSAPs, etc. may also
      trigger a mapping request.

   Ma22.  Validation of civic location: The mapping protocol MUST
      implement a method via a mapping request, that makes it possible
      for a mapping server to validate a civic location prior to that
      location's use in an actual emergency call.

      Motivation: Location validation provides an opportunity to help
      assure ahead of time, whether successful mapping to the
      appropriate PSAP will likely occur when it is required.
      Validation may also help to avoid delays during emergency call
      setup due to invalid locations.

   Ma23.  Validation resolution: The mapping protocol MUST support
      (i.e., required to implement, but not required for use) the return
      of additional information which can be used to determine the
      precision or resolution of the data elements used to determine a
      PSAP URI.

      Motivation: The mapping server may not use all the data elements
      in the provided location information to determine a match, or may
      be able to find a match based on all of the information except for
      some specific data elements.  The uniqueness of this information
      set may be used to differentiate among emergency jurisdictions.
      Precision or resolution in the context of this requirement might
      mean, for example, explicit identification of the data elements
      that were used successfully in the mapping.

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   Ma24.  Indication of non-existent location: The protocol MUST support
      a mechanism to indicate that a location or a part of a location is
      known to not exist, even if a valid location-to-PSAP URI mapping
      can be provided.  This includes a way to identify a separate
      mechanism to resolve any such discrepancy.

      Motivation: The emergency authority for a given jurisdiction may
      provide a means to resolve addressing problems, e.g., a URI for a
      web service that can be used to report problems with an address.

   Ma25.  Limits to validation: Successful validation of a civic
      location MUST NOT be required to place an emergency call.

      Motivation: In some cases, a civic location may not be considered
      valid.  This fact should not result in the call being dropped or
      rejected by any entity along the signaling path to the PSAP.

   Ma26. 3D sensitive mapping: The mapping protocol MUST implement
      support for both 2D and 3D location information, and may accept
      either a 2D or 3D mapping request as input.

      Motivation: It is expected that provisioning systems will accept
      both 2D and 3D data.  When a 3D request is presented to an area
      only defined by 2D data, the mapping result would be the same as
      if the height/altitude dimension was omitted in the request.

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8.  Security Considerations

   Security considerations are discussed in the ECRIT security document
   I-D.taylor-ecrit-security-threats [4] .

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9.  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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10.  Acknowledgments

   In addition to thanking those listed above, we would like to also
   thank Guy Caron, Barry Dingle, Keith Drage, Tim Dunn, Patrik
   Faeltstroem, Clive D.W. Feather, Raymond Forbes, Randall Gellens,
   Michael Haberler, Michael Hammer, Ted Hardie, Gunnar Hellstrom,
   Cullen Jennings, Marc Linsner, Rohan Mahy, Patti McCalmont, Don
   Mitchell, John Morris, Andrew Newton, Steve Norreys, Jon Peterson,
   James Polk, Benny Rodrig, John Rosenberg, Jonathan Rosenberg, John
   Schnizlein, Shida Schubert, James Seng, Byron Smith, Tom Taylor,
   Barbara Stark, Hannes Tschofenig, and Nate Wilcox, for their
   invaluable input.

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11.  References

11.1.  Normative References

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

   [2]  Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
        Configuration Protocol Option for Coordinate-based Location
        Configuration Information", RFC 3825, July 2004.

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

   [4]  Schulzrinne, H., "Security Threats and Requirements for
        Emergency Call Marking and Mapping",
        draft-taylor-ecrit-security-threats-03 (work in progress),
        March 2006.

   [5]  Schulzrinne, H., "A Uniform Resource Name (URN) for Services",
        draft-ietf-ecrit-service-urn-00 (work in progress),
        February 2006.

   [6]  Hardie, T., "LoST: A Location-to-Service Translation Protocol",
        draft-hardie-ecrit-lost-00 (work in progress), March 2006.

   [7]  Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
        and DHCPv6) Option for Civic  Addresses Configuration
        Information", draft-ietf-geopriv-dhcp-civil-09 (work in
        progress), January 2006.

11.2.  Informative References

   [8]   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.

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

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

   [11]  Wijk, A., "Framework of requirements for real-time text
         conversation using SIP", draft-ietf-sipping-toip-03 (work in
         progress), September 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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