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ecrit                                                           B. Rosen
Internet-Draft                                                   NeuStar
Intended status: Standards Track                                 J. Polk
Expires: April 18, 2007                                    Cisco Systems
                                                        October 15, 2006

    Best Current Practice for Communications Services in support of
                           Emergency Calling

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on April 18, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).


   Requesting help in an emergency using a communications device such as
   a telephone or mobile is an accepted practice in most of the world.
   As communications devices increasingly utilize the Internet to
   interconnect and communicate, users will continue to expect to use
   such devices to request help, regardless of whether or not they
   communicate using IP.  The emergency response community will have to

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   upgrade their facilities to support the wider range of communications
   services, but cannot be expected to handle wide variation in device
   and service capability.  The IETF has several efforts targeted at
   standardizing various aspects of placing emergency calls.  This memo
   describes best current practice on how devices and services should
   use such standards to reliably make emergency calls

Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Which devices and services should support emergency calls  . .  4
   4.  Determining Location . . . . . . . . . . . . . . . . . . . . .  4
   5.  Determining an emergency call  . . . . . . . . . . . . . . . .  7
   6.  Session Signaling  . . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  SIP signaling requirements for User Agents . . . . . . . .  8
     6.2.  Mapping from Location to a PSAP URI  . . . . . . . . . . .  9
     6.3.  Routing the call . . . . . . . . . . . . . . . . . . . . . 10
     6.4.  Responding to PSAP signaling . . . . . . . . . . . . . . . 10
     6.5.  Disabling of features  . . . . . . . . . . . . . . . . . . 11
   7.  Testing  . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Testing Mechanism  . . . . . . . . . . . . . . . . . . . . 11
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
   Intellectual Property and Copyright Statements . . . . . . . . . . 16

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1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Introduction

   This document describes how SIP User Agents and proxy servers support
   emergency calling, as outlined in [framework].  Here, an emergency
   call refers to a communications session established by a user to a
   "Public Safety Answering Point" (PSAP) which is a call center
   established by response agencies to accept emergency calls.  We
   differentiate such calls from other sessions which are created by
   responders using public communications infrastructure often involving
   some kind of priority access as defined in Emergency
   Telecommunications Service (ETS) in IP Telephony [RFC4190].

   Making an emergency call involves the use of location information,
   referring to the physical location of the caller.  Location is used
   within the emergency calling system to route a call to the correct
   PSAP, as well as by the PSAP to choose the correct responder, and
   direct them to the person in need of assistance.

   The steps involved in an emergency call from an IP based device are
   (with a rough ordering of operation)
   1.  Device connects to access network, and obtains initial location
   2.  User dials visited location's emergency number
   3.  User device identifies call as emergency call
   4.  User device includes location indication (by value or by
       reference) in the call set-up messaging
   5.  emergency call set-up is routed to appropriate PSAP based on
       location of the caller
   6.  call is established with PSAP
   7.  caller's location is presented to PSAP operator for dispatch

   As a quick overview for a typical Ethernet connected telephone using
   SIP signaling:
   o  the phone "boots" and connects to its access network
   o  the phone would get location from the DHCP server [or an L7
   o  It would use "urn:service:sos" as the URI of an emergency call.
   o  It would determine the PSAP's URI by using the
      [I-D.ietf-ecrit-lost] mapping server from the location provided in
      the signaling

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   o  It would put its location in the SIP INVITE as a PIDF-LO in the
      body of the INVITE (or a reference to location in a Location
      header) and forward the call to its first hop proxy.
   o  The proxy recognizes the call as an emergency call and routes the
      call using normal SIP routing mechanisms
   [RFC4504] details Best Current Practice for SIP user agents.  This
   memo can be considered an addition to it for endpoints.

3.  Which devices and services should support emergency calls

   Although present PSAPs have only support for voice calls placed
   through PSTN facilities or systems connected to the PSTN, future
   PSAPs will support Internet connectivity and a wider range of media
   types.  In general, if a user could reasonably expect to be able to
   call for help with the device, then the device or service should
   support emergency calling.  Certainly, any device or service that
   looks like and works like a telephone (wired or mobile) should
   support emergency calling, but increasingly, users have expectations
   that other devices and services should work.

   Using current (evolving) standards, devices that create media
   sessions and exchange audio, video and/or text, and have the
   capability to establish sessions to a wide variety of addresses, and
   communicate over private IP networks or the Internet, should support
   emergency calls.

4.  Determining Location

   With Internet based communications services, determining where the
   caller is located is more problematic than in PSTN and mobile
   systems.  Existing wired phones are tethered with a wire that is
   connected directly to a call control device, a circuit switch.
   Cellular phones are tethered via a radio channel to a cell tower,
   which connects that cell phone to a circuit switch.  The primary
   difficulty with IP based phones is that the connectivity, whether
   wired or radio channel, is decoupled from the call control device.
   The communications service may not have any relationship with the
   access network carrier, and, with NAT and VPN tunnels, may have no
   way to even find out who the access carrier is.

   For this reason, standards have been created for endpoints (devices)
   to obtain location information where it is the access network that
   knows the location of the endpoint.  To obtain location information,
   the endpoint can use a Location Configuration Protocol.  The endpoint
   is a subscriber to both the access network and the communications
   service, and thus is in a position to obtain its location from the

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   access network, and supply it to the communications service.  These
   issues, and the necessity for endpoints and access networks to
   support LCPs is detailed in [framework].

   For devices that operate on a network where the network operator
   controls the specification of every device connected to that network
   that could be used for emergency calls, the method by which location
   is determined need not be an IETF standard, but can be any method
   that achieves the desired result.  Such a method MUST be specified,
   and every device MUST support it.

   For all other devices, location configuration by DHCP, [Placeholder
   for L7 LCP] and LLDP-MED MUST be supported.  DHCP [RFC2131] has been
   enhanced to provide the location of a device.  [RFC3825] describes
   how a geo-location (lat/lon/alt) may be obtained and
   [I-D.schulzrinne-geopriv-dhcp-civil] describes how a civic (street
   address) location can be obtained via DHCP.

   [Placeholder for HELD, LCP or other L7 location determination

   [LLDP] with [LLDP-MED] extensions provides an alternative to DHCP in
   many enterprise environments.

   For devices that operate in a network where the network operator
   controls the specification of every device connected to that network,
   but the network attachment supports upstream networks to which
   communications devices are connected (such as any network that
   supports Ethernet connected telephones and terminal adapters), the
   method by which location is determined need not be an IETF standard,
   but can be any method which achieves the desired result.  However,
   the network attachment MUST support at least one of DHCP [L7 LCP] or
   LLDP-MED for upstream communications devices to obtain location.  For
   smaller interior (e.g, LAN) networks, the DHCP, [L7 LCP] or LLDP-MED
   server should simply repeat the location obtained from the access
   network.  For larger networks, other mechanisms, such as a DHCP Relay
   Agent [RFC3046] SHOULD be used to provide more accurate location of

   For devices that operate on a network where the network operator does
   not control the specification of every device connected to the
   network, at least one of DHCP, [L7 LCP] or LLDP-MED MUST be supported
   on the network.

   Self Reported location is generally unacceptable in emergency calls,
   although it is being used prior to automatic location determination
   schemes being fielded.  Local laws may govern what is acceptable in
   any country or area.  Devices and/or access networks SHOULD support a

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   manual method to "override" the location the access network
   determines.  The access network generally only knows the location of
   its demarcation point between the access network and the subscriber.
   The subscriber could have an extended network behind the demarc
   unknown to the access network.  A method to account for this
   condition SHOULD be provided.

   Devices SHOULD get location immediately after obtaining local network
   configuration information.  It is essential for the location to be
   determined BEFORE any VPN tunnels are established.  It is equally
   essential that this location information is *not* overwritten by any
   process engaged from establishing a VPN connection.  In other words,
   the established VPN to Chicago from the device in Dallas should not
   overwrite the Dallas location for any reason especially an emergency

   It is desirable that location information be periodically refreshed.
   For devices which are not expected to roam, refreshing on the order
   of once per day is RECOMMENDED.  For devices which roam, refresh of
   location SHOULD be more frequent, with the frequency related to the
   mobility of the device and the ability of the access network to
   support the refresh operation.  There can be instances in which a
   device is aware of when it moves, for example when it changes access
   points.  When this type of event occurs, the device SHOULD refresh
   its location.

   It is desirable for location information to be requested immediately
   before placing an emergency call.  However, if there is any delay in
   getting more recent location, the call SHOULD be placed with the most
   recent location information the device has.  It is RECOMMENDED that
   the device not wait longer than 1 sec to obtain updated location, and
   systems should ideally be designed such that the typical response is
   under 100ms.  These numbers are empirically derived, but are intended
   to keep total call signaling time below 2 seconds.  There are
   conflicts between the time it takes to generate location when
   measuring techniques are used and the desire to route the call
   quickly.  If an accurate location cannot be determined quickly, a
   rough location SHOULD be returned within 100ms which can be used to
   route the call.  The location of the nearest base station in a
   wireless network is an example of a rough location.

   If the LCP does not return location in the form of a PIDF-LO
   [RFC4119], the endpoint must map the location information it receives
   from the configuration protocol to a PIDF-LO.

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5.  Determining an emergency call

   An emergency call is distinguished by the device (or a downstream
   element) by an "address", which in most cases for Internet connected
   devices is still a dialstring, although other user interfaces may be

   Note: It is undesirable to have a single "button" emergency call user
   interface element.  These mechanisms have a very high false call
   rate.  PSAPs prefer devices to use their local emergency call

   While in some countries there is a single 3 digit dialstring that is
   used for all emergency calls (i.e. 911 in North America), in some
   countries there are several 3 digit numbers used for different types
   of calls.  For example, in Switzerland, 117 is used to call police,
   118 is used to call the fire brigade, and 144 is used for emergency
   medical assistance.  In other countries, there are no "short codes"
   or "service codes" for 3 digit dialing of emergency services and
   local (PSTN) numbers are used.

   [I-D.schulzrinne-sipping-service] introduces a universal emergency
   service URN scheme.  On the wire, emergency calls SHOULD include this
   type of URI as a Route header [RFC3261].  The scheme includes a
   single emergency URN (urn:service:sos) and responder specific ones
   (urn:service:sos.police).  Using the service:sos URN scheme,
   emergency calls can be recognized as such throughout the Internet.

   Devices MUST use the service:sos URN scheme to mark emergency calls.

   To determine which calls are emergency calls, some entity needs to
   map a user entered dialstring into this URN scheme.  A user may
   "dial" 1-1-2, but the call would be sent to urn:service:sos.  This
   mapping is SHOULD performed at the endpoint device, but MAY be
   performed at an intermediate entity (such as a SIP proxy server).

   Note: It is strongly RECOMMENDED that devices recognize the emergency
   dialstring(s) and map to the universal emergency URN.  If devices
   cannot do "dial plan interpretation", then the first signaling aware
   element (first hop proxy in SIP signaled devices) SHOULD do the
   mapping.  It is important to not require a large number of active
   elements handle a call before it is recognized as an emergency call

   In systems that support roaming, there may be a concept of "visited"
   and "home" networks.  Even when there is not a "visited network", the
   user may be roaming (or nomadic) in a different country from their
   home.  This gives rise to the problem of which dialstring(s) to
   recognize, the "home" or "visited"?  While it is desirable that the

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   "home" dialstrings be recognized, it is required (by law in some
   countries) that the "visited" dialstrings be recognized.  Dial plan
   interpretation may need to take "visited" emergency dialstrings into

   To give an example of this difference in dialstrings: If the device
   is from North America, the home and visited emergency dialstring is
   "9-1-1".  If that devices roams to the UK, the home emergency
   dialstring is still "9-1-1", but the visited emergency dialstring
   would become "9-9-9".  If the device roams to Paris, the home
   dialstring remains the same, "9-1-1", but the visited dialstring
   changes from 999 to "1-1-2".

   The home emergency dialstrings MAY be provisioned into the device (or
   other element doing dialstring to universal emergency call URN
   mapping).  [I-D.ietf-ecrit-lost]) provides dialstrings for a given
   location and SHOULD be used by devices to learn the local (i.e.
   "visited" dialstrings.

6.  Session Signaling

   SIP signaling [RFC3261] is expected be supported by upgraded PSAPs.
   Gateways MAY be used between Internet connected devices and older
   PSAPs.  Some countries may support other signaling protocols into

6.1.  SIP signaling requirements for User Agents

   The initial signaling Method is INVITE.
   1.   The Request URI SHOULD be a PSAP URI obtained from LoST (see
        Section 6.2).  If the device cannot access a LoST server, the
        To: SHOULD be a service URN in the "sos" tree.  If the device
        cannot do local dialstring interpretation, the Request URI:
        SHOULD be a dialstring URI [I-D.rosen-iptel-dialstring]with the
        dialed digits. sips MUST be specified, unless the operation must
        be retried due to a failure to establish a TLS connection.
   2.   The To: header MUST be present and SHOULD be a service URN in
        the "sos" tree.  If the device cannot do local dialstring
        interpretation, the To: SHOULD be a dialstring URI with the
        dialed digits. sips MUST be specified, unless the operation must
        be retried due to a failure to establish a TLS connection.
   3.   The From: header MUST be present and SHOULD be the AoR of the

        NOTE: unintialized devices may not have an AoR available

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   4.   A Via: header MUST be present and SHOULD include the URI of the
   5.   A Route header SHOULD be present with the service URN in the
        "sos" tree, and the loose route parameter.
   6.   Either a P-Asserted-Identity [RFC3325] or an Identity header
        [RFC4474], or both, SHOULD be included to identify the sender.
   7.   A Contact header MUST be present (which might contain a GRUU
        [I-D.ietf-sip-gruu]) to permit an immediate call-back to the
        specific device which placed the emergency call.
   8.   Other headers MAY be included as per normal sip behavior
   9.   A Supported: header MUST be included with the 'geolocation'
        option tag[I-D.ietf-sip-location-conveyance], unless the device
        does not understand the concept of SIP Location ;
   10.  If the device's location is by-reference, a Geolocation:
        header[I-D.ietf-sip-location-conveyance] MUST be present
        containing the URI of the PIDF-LO reference for that device;
   11.  if a device understands the SIP Location Conveyance
        [I-D.ietf-sip-location-conveyance] extension and has its
        location available, it MUST include location either by-value or
        by-reference.  If it is by-value, the INVITE contains a
        Supported header with a "geolocation" option tag, and a "cidURL"
        [RFC2396]as the value in the Geolocation header, indicating
        which message body part contains the PIDF-LO.  If the INVITE
        contains a location by-reference, it includes the same Supported
        header with the "geolocation" option tag, and includes the URI
        of the PIDF-LO on a remote node in a Geolocation header.
        [I-D.ietf-geopriv-pdif-lo-profile] MUST be used
   12.  If a device understand the SIP Location Conveyance extension and
        has its location unavailable or unknown to that device, it MUST
        include a Supported header with a "geolocation" option tag, and
        not include a Geoocation header, and not include a PIDF-LO
        message body.;
   13.  A normal SDP offer SHOULD be included in the INVITE.  The offer
        SHOULD NOT include compressed audio codecs, although a wideband
        codec offer MAY be included.

   Note: Silence suppression (Voice Activity Detection methods) MUST NOT
   be used on emergency calls.  PSAP call takers sometimes get
   information on what is happening in the background to determine how
   to process the call.

6.2.  Mapping from Location to a PSAP URI

   To route an emergency call, we make use of the [I-D.ietf-ecrit-lost]
   mapping service which takes a location expressed by a PIDF-LO and
   returns one or more PSAP URIs.  The request includes the service URN
   which is used to determine which entity should receive the call.
   Ideally, mapping from location to the PSAP URI would be accomplished

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   at the time the emergency call is placed.  However, it could be that
   when the emergency occurs, the LoST server is unavailable to the
   caller, or busy.  To guard against that, devices MUST cache a
   mapping.  The mapping MUST be performed at boot time, and whenever
   the location changes such that the previous mapping may no longer
   valid.  To facilitate this operation, LoST provides a mechanism that
   a device can use to determine when it should refresh the mapping.
   Devices where location changes SHOULD use this mechanism to maintain
   a desired mapping.

   User agents that can obtain location information MUST perform the
   mapping from location information to PSAP URI using
   [I-D.ietf-ecrit-lost].  The mapping is performed whenever the UA
   acquires new location information that is outside the bounds of the
   current PSAP coverage region specified in the LoST response or the
   time-to-live value of that response has expired.

   All proxies in the outbound path SHOULD recognize emergency calls
   with a Request URI of the service URN in the "sos" tree.  A proxy
   recognizing such a call (which indicates that the endpoint understood
   the call was an emergency call, but was unable to map its location to
   a PSAP URI) MUST perform the LoST mapping and retarget the call to
   the PSAP URI (the service URN SHOULD remain as a Route header).

   To deal with old user agents that predate this specification and with
   UAs that do not have access to their own location data, proxies that
   recognize a call as an emergency call that is not marked as such (see
   Section 5) or where the Request-URI is a service:sos URN MUST also
   perform this mapping, with the best location it has available for the
   endpoint.  The resulting PSAP URI would become the Request URI.

6.3.  Routing the call

   Normal routing mechanisms for the specified URI should be used.  For
   SIP signaled devices, the domain of the URI should be extracted, and
   the DNS consulted for a sip (or sips) SRV.  The resulting NAPTR, if
   present, should be used for the FQDN of the server.

6.4.  Responding to PSAP signaling

   The PSAP is expected to use normal signaling (e.g.  SIP) as per IETF
   standards.  Devices and proxies should expect to:
   1.  Be REFERed to a conference bridge; PSAPs often include
       dispatchers, responders or specialists on a call.
   2.  Be REFERed to a secondary PSAP.  Some responder's dispatchers are
       not located in the primary PSAP.  The call may have to be
       transferred to another PSAP.  Most often this will be an attended
       transfer, or a bridged transfer.

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   3.  (For devices that are Mobile) SUBSCRIBE to the Presence of the
       AoR (or equivalent for other signaling schemes) to get location
   4.  Support Session Timer (or equivalent) to guard against session

   Devices with an active emergency call (i.e.  SIP Dialog) MUST NOT
   generate a BYE request (or equivalent for other non-SIP signaling).
   The PSAP must be the only entity that can terminate a call.  If the
   user "hangs up" an emergency call, the device should ring, and when
   answered, reconnect the caller to the PSAP.

   There can be a case where the session signaling path is lost, and the
   user agent does not receive the BYE.  If the call is hung up, the
   session timer expires, and 5 minutes elapses from the last message
   received by the device from the PSAP, the call may be declared lost.
   If in the 5 minute interval an incoming call is received from the
   domain of the PSAP, the device should drop the old call and alert for
   the (new) incoming call.

6.5.  Disabling of features

   The calling device and/or service SHOULD disable outgoing call
   features such as:
   o  Call Waiting
   o  Call Transfer
   o  Three Way Call
   o  Flash hold
   o  Outbound Call Blocking

   The emergency dialstrings SHOULD NOT be permitted in Call Forward
   numbers or speed dial lists.

   The device and/or service SHOULD disable the following incoming call
   features on calls from the PSAP:
   o  Call Waiting (all kinds)
   o  Do Not Disturb
   o  Call Forward (all kinds) (if the PSAP calls back within some
      (30min?) interval)

7.  Testing

7.1.  Testing Mechanism

   INVITE requests to a service urn with a urn parameter of "test"
   indicates a request for an automated test.  For example,
   "urn:service.sos.fire;test".  As in standard SIP, a 200 (OK) response

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   indicates that the address was recognized and a 404 (Not found) that
   it was not.  A 486 (Busy Here) should be returned if the test service
   is busy, and a 488 (Not Acceptable Here) should be returned if the
   PSAP does not support the test mechanism.

   In its response to the test, the PSAP MAY include a text body
   indicating the identity of the PSAP, the requested service, and the
   location reported with the call.  For the latter, the PSAP SHOULD
   return location-by-value even if the original location delivered with
   the test was by-reference.

   A PSAP accepting a test call SHOULD accept a media loopback
   test[I-D.ietf-mmusic-media-loopback] and SHOULD support the "rtp-pkt-
   loopback" and "rtp-start-loopback" options.  The user agent would
   specify a loopback attribute of "loopback-source", the PSAP being the
   mirror.  User Agents should expect the PSAP to loop back no more than
   3 packets of each media type accepted, after which the PSAP would
   normally send BYE.

   User agents SHOULD perform a full call test, including media
   loopback, after a disconnect and subsequent change in IP address.
   After an initial IP address assignment test, a full test SHOULD be
   repeated approximately every 30 days with a random interval.

   User agents MUST NOT place a test call immediately after booting, as
   a widespread power outage and subsequent restoration would impose an
   inordinate load on the emergency call routing system.

   PSAPs MAY refuse repeated requests for test from the same device in a
   short period of time.

8.  Security Considerations

   There are no new security considerations beyond those in the
   normative references.  This memo does not introduce any new
   protocols; it specifies use of several of them.  Implementers are
   admonished to ,,,

9.  Normative References

              Hardie, T., "LoST: A Location-to-Service Translation
              Protocol", draft-ietf-ecrit-lost-01 (work in progress),
              September 2006.


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              Tschofenig, H., "GEOPRIV PIDF-LO Usage Clarification,
              Considerations and Recommendations",
              draft-ietf-geopriv-pdif-lo-profile-04 (work in progress),
              May 2006.

              Hedayat, K., "An Extension to the Session Description
              Protocol (SDP) for Media Loopback",
              draft-ietf-mmusic-media-loopback-05 (work in progress),
              September 2006.

              Rosenberg, J., "Obtaining and Using Globally Routable User
              Agent (UA) URIs (GRUU) in the  Session Initiation Protocol
              (SIP)", draft-ietf-sip-gruu-10 (work in progress),
              August 2006.

              Polk, J. and B. Rosen, "Session Initiation Protocol
              Location Conveyance",
              draft-ietf-sip-location-conveyance-04 (work in progress),
              August 2006.

              Wijk, A. and G. Gybels, "Framework for real-time text over
              IP using the Session Initiation Protocol  (SIP)",
              draft-ietf-sipping-toip-07 (work in progress),
              August 2006.

              Rosen, B., "Dialstring parameter for the Session
              Initiation Protocol Uniform Resource  Identifier",
              draft-rosen-iptel-dialstring-04 (work in progress),
              June 2006.

              Schulzrinne, H., "DHCP Option for Civil Location",
              draft-schulzrinne-geopriv-dhcp-civil-01 (work in
              progress), February 2003.

              Schulzrinne, H., "A Uniform Resource Name (URN) for
              Services", draft-schulzrinne-sipping-service-01 (work in
              progress), October 2005.

   [LLDP]     "IEEE802.1ab Station and Media Access Control", Dec 2004.


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Internet-Draft          Emergency Call Phone BCP            October 2006

              TIA, "ANSI/TIA-1057 Link Layer Discovery Protocol - Media
              Endpoint Discovery".

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

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC2396]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifiers (URI): Generic Syntax", RFC 2396,
              August 1998.

   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",
              RFC 3046, January 2001.

   [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.

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              November 2002.

   [RFC3825]  Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
              Configuration Protocol Option for Coordinate-based
              Location Configuration Information", RFC 3825, July 2004.

   [RFC4103]  Hellstrom, G. and P. Jones, "RTP Payload for Text
              Conversation", RFC 4103, June 2005.

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

   [RFC4190]  Carlberg, K., Brown, I., and C. Beard, "Framework for
              Supporting Emergency Telecommunications Service (ETS) in
              IP Telephony", RFC 4190, November 2005.

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474, August 2006.

   [RFC4504]  Sinnreich, H., Lass, S., and C. Stredicke, "SIP Telephony
              Device Requirements and Configuration", RFC 4504,
              May 2006.

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Internet-Draft          Emergency Call Phone BCP            October 2006

              Rosen, B., Polk, J., Schulzrinne, H., and A. Newton,
              "Framework for Emergency Calling in Internet Multimedia",
              October 2006.

Authors' Addresses

   Brian Rosen
   470 Conrad Dr.
   Mars, PA  16046

   Phone: +1 724 382 1051
   Email: br@brianrosen.net

   James M. Polk
   Cisco Systems
   3913 Treemont Circle
   Colleyville, TX  76034

   Phone: +1-817-271-3552
   Email: jmpolk@cisco.com

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Full Copyright Statement

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