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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 draft-ietf-sipcore-location-conveyance

SIP Working Group                                            James Polk
Internet Draft                                            Cisco Systems
Expiration: May 16th, 2008                                  Brian Rosen
Intended Status: Standards Track (PS)                           NeuStar




         Location Conveyance for the Session Initiation Protocol
               draft-ietf-sip-location-conveyance-09.txt
                             Nov 16th, 2007


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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document defines an extension to the Session Initiation
   Protocol (SIP) to convey geographic location information from one
   SIP entity to another SIP entity.  The extension covers end to end
   conveyance as well as location-based routing, where proxy servers
   make routing decisions based on the location of the SIP user agents.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Conventions used in this document . . . . . . . . . . . . . .  4
   3.  Mechanisms  . . . . . . . . . . . . . . . . . . . . . . . . .  4
       3.1 Overview of SIP Location Conveyance . . . . . . . . . . .  4
       3.2 The Geolocation Header  . . . . . . . . . . . . . . . . .  5
       3.3 424 (Bad Location Information) Response Code  . . . . . .  8
       3.4 The Geolocation-Error Header  . . . . . . . . . . . . . .  9
       3.5 The Geolocation Option Tag  . . . . . . . . . . . . . . . 18
       3.6 Using sip/sips/pres as a Dereference Scheme . . . . . . . 19
   4.  Geolocation Examples  . . . . . . . . . . . . . . . . . . . . 20
       4.1 Location-by-value (Coordinate Format) . . . . . . . . . . 20
       4.2 Location-by-reference . . . . . . . . . . . . . . . . . . 22
   5.  SIP Element Behavior  . . . . . . . . . . . . . . . . . . . . 23
       5.1 UAC Behavior  . . . . . . . . . . . . . . . . . . . . . . 24
       5.2 UAS Behavior  . . . . . . . . . . . . . . . . . . . . . . 26
       5.3 Proxy Behavior  . . . . . . . . . . . . . . . . . . . . . 29
   6.  Geopriv Privacy Considerations  . . . . . . . . . . . . . . . 32
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . 33
   8.  IANA Considerations   . . . . . . . . . . . . . . . . . . . . 34
       8.1 IANA Registration for New SIP Geolocation Header  . . . . 34
       8.2 IANA Registration for New SIP Geolocation Option Tag  . . 35
       8.3 IANA Registration for New 424 Response Code . . . . . . . 35
       8.4 IANA Registration for New SIP Geolocation-Error Header  . 35
       8.5 IANA Registration for New SIP Geolocation-Error Codes . . 35
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 37
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . 37
       10.1 Normative References   . . . . . . . . . . . . . . . . . 37
       10.2 Informative References . . . . . . . . . . . . . . . . . 38
       Author Information  . . . . . . . . . . . . . . . . . . . . . 38
       Appendix A. Requirements for SIP Location Conveyance  . . . . 39
       Appendix B. Example of Civic-based PIDF-LO w/ S/MIME  . . . . 41
       Intellectual Property and Copyright Statements  . . . . . . . 42


1.  Introduction

   This document describes how Location can be "conveyed" (that is,
   transmitted over the Internet) from one SIP user agent (UA), or in
   some circumstances, a proxy server acting in support of a UA, to
   another entity using SIP [RFC3261].  Here "Location" is a
   description of the physical geographical area where something
   currently exists.  The phrase "location conveyance" describes
   scenarios in which a SIP user agent client (UAC) is informing a user
   agent server  (UAS), or intermediate SIP server where the UAC is.  A
   superset of this can also be true as well, in which one UA(1) is
   telling another UA(2) where another Target is, meaning not
   necessarily where UA(1) is.  The key to this is whether UA(1) has
   permission to retransmit that other Target's location.  If yes, then
   this is valid.  If no, then this is breaking a fundamental rule
   within this extension.


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   Location Conveyance is different from a UAC seeking the location the
   UAS.  Location conveyance is a 'sending location out in the request'
   model, where 'asking that someone else's location be in a response'
   is not discussed here.

   Geographic location in the IETF is discussed in RFC 3693 (Geopriv
   Requirements) [RFC3693].  It defines a "Target" as the entity whose
   location is being sought.  In this case, this is the UA's
   (UA) location.  A [RFC3693] "Using Protocol" defines how a "location
   Server" transmits a "Location Object" to a "Location Recipient"
   while maintaining the contained privacy intentions of the Target
   intact. This document describes the extension to SIP for how it
   complies with the Using Protocol requirements, where the location
   server is a UA or Proxy Server and the Location Recipient is
   another UA or Proxy Server.

   Location can be transmitted by-value or by-reference.  The location
   "value" in this SIP extension is in the form of a Presence
   Information Data Format - Location Object, or PIDF-LO, as described
   in [RFC4119].  A PIDF-LO is an XML Scheme specifically for carrying
   geographic location of a Target.  Location-by-value refers to a UA
   including a PIDF-LO as a body part of a SIP message, sending that
   Location Object to another SIP element.  Location-by-reference
   refers to a UA or proxy server including a URI in a SIP message
   header field which can be dereferenced by a Location Recipient for a
   Location Object, in the form of a PIDF-LO.  Dereferencing can be by
   a SIP UA or a SIP server.

   As recited in RFC 3693, location often must be kept private.  The
   Location Object (PIDF-LO) contains rules which provides guidance to
   the Location Recipient and controls onward distribution and
   retention of the location.  This document describes the security and
   privacy considerations that must be applied to location conveyed
   with SIP.

   Another use for location is location-based routing of a
   SIP request, where the choice of the next hop (and usually, the
   outgoing Request-URI) is determined by the location of the UAC which
   is in the message by-value or by-reference.  This document describes
   how location can be conveyed from the UAC, or a proxy acting on its
   behalf, to a routing proxy.  How the location is actually used to
   determine the next hop or Request-URI is beyond the scope of this
   document.

   We refer to the "emergency case".  This refers to a specific,
   important use of SIP location conveyance where the location of the
   caller is used to determine which Public Safety Answering Point
   (PSAP) is expected to receive an emergency call request for help
   (e.g., a call to 1-1-2 or 9-1-1).  This is an example of
   location-based routing.  The location conveyed is also used by the
   PSAP to dispatch first responders to the caller's location.  There


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   are special security considerations, which make the emergency case
   unique, compared to a normal location conveyance within SIP.


2.  Conventions used in this document

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

3.  Mechanisms

3.1 Overview of SIP Location Conveyance

   This document defines a new SIP header: Geolocation.  The
   Geolocation header field contains a URI which can either be a "cid:"
   URI (Content Identification), per [RFC2392], or a
   location-by-reference URI to be dereferenced by a Location Recipient
   to retrieve the location of the Target UA.

   Where the Geolocation header contains a "cid:", the URI points to a
   message body that is in the form of a PIDF [RFC3863], which was
   extended in [RFC4119] to include location, as a PIDF-LO. This is
   location-by-value, the actual location information in the PIDF-LO is
   included in the body of the message.

   If the URI in the Geolocation header field is a scheme other than
   "cid:", another protocol operation is needed by the SIP message
   recipient to obtain the location of the Target (UA).  This is
   location-by-reference. This document describes how a SIP presence
   subscription [RFC3856] can be used as a dereference protocol.

   The Geolocation header, either with the PIDF-LO in a body or as a
   location-by-reference URI, can be included by a UA in a
   SIP message.  A SIP proxy server may assert location of the UA by
   inserting the header field, which must specify a
   location-by-reference URI.  Since body parts cannot be inserted by a
   SIP proxy server, location-by-value message body cannot be inserted
   by a proxy.

   The Geolocation header can have parameters that are associated
   with a URI in the header field.  The "inserted-by" parameter has
   values of "endpoint" or "server", indicating which entry added
   location to the message. This header parameter MAY be added every
   time a new location is added into a message.

   Retargeting means the Request-URI of the request has changed to
   point at a new destination UAS.  This is different than message
   routing, that all SIP proxies do.  If a SIP request is retargeted
   based on the location contained or referenced within that message,
   the "used-for-routing" parameter MUST be added as a header parameter


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   within the appropriate locationValue.

   There is no mechanism by which the veracity of these parameters can
   be verified.  They are hints to downstream entities on how the
   location information in the message was originated and used.

   This document creates a new option tag: geolocation, to indicate
   support for the this extension by UAs.

   A new error message (424 Bad Location Information) is also defined
   in this document. Within this response is a new header indicating
   location-based errors, call the Geolocation-Error header.  This
   header has various codes that provide additional information about
   the type of location error experienced by a Location Recipient.

   Both new headers, the header parameters, the new option-tag, the new
   error response, and Geolocation-Error codes are IANA registered by
   this document.


3.2 The Geolocation Header

   This document defines and IANA registers a new SIP header:
   Geolocation.  The Geolocation header field MUST contain at least one
   of two types of URIs:

   o  a location-by-reference URI, or

   o  a content-ID indicating where location is within the message body
      of this message

   A location-by-reference URI is a pointer to a record on a remote
   node containing location of the location Target, typically the
   UA in this transaction.

   A location-by-value content-ID (cid-url) [RFC2392] indicates which
   message body part contains location for this UA.

   The Geolocation header has the following BNF syntax:

   Geolocation        =  "Geolocation" HCOLON (locationValue *(COMMA
                          locationValue))
   locationValue      =  LAQUOT locationURI RAQUOT *(SEMI geoloc-param)
   locationURI        =  sip-URI / sips-URI / pres-URI
                          / cid-url ; (from RFC 2392)
                          / absoluteURI ; (from RFC 3261)
   geoloc-param       =  "inserted-by" EQUAL geoloc-inserter
                          / "used-for-routing"
                          / "recipient" EQUAL recipient-type
                          / generic-param ; (from RFC 3261)
   geoloc-inserter    =  host-id
                          / gen-value ; (from RFC 3261)


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   recipient-type     =  "endpoint" / "routing-entity" / "both"
                          / gen-value ; (from RFC 3261)

   sip-URI, sips-URI and absoluteURI are defined according to RFC 3261.
   The pres-URI is defined in RFC 3859 [RFC3859].

   The cid-url is defined in [RFC2392] to locate message body
   parts.  This URI type MUST be present in a SIP message if location
   is by-value in that same message.

   Other protocols used in the Location URI MUST be reviewed against
   the RFC 3693 criteria for a Using Protocol.

   The Geolocation header MAY have one or more locationValues. SIP
   servers inserting a locationValue MUST add the new value to the end
   of the header value, such that the last locationValue in the header
   is the most recent one added to the message.

   A locationValue has the following independent header parameters,

   o  the "inserted-by=" parameter provides the host-id
      (alice.example.com -- which is the same as the "sent-by"
      parameter in a Via header) of the SIP entity that inserted this
      locationValue into the request. This is used to map to any
      Geolocation-Error message to determine which location, if there
      is more than one in a request, the error corresponds to.  If an
      entity receives an Geolocation-Error with a host-id not of this
      entity, the Geolocation-Error SHOULD be ignored.

   o  the "used-for-routing" parameter to inform recipients that the
      location in this locationValue was used to route the message
      towards the ultimate destination UAS.  This can occur more than
      once along the request's path.  Because locationValues are
      inserted as last inserted is last in the header, the last
      locationValue is the most recent one added to the message.  This
      also gives the "used-for-routing" header parameter added
      integrity - as the receiving SIP entity knows which locationURI
      the message was routed upon.

   o  the "recipient=" parameter to allow recipients to infer what SIP
      element type this locationValue was intended to be for.  The
      types are

         o "endpoint" - meaning the ultimate destination UAS;

         o "routing-entity" - meaning SIP servers that route messages
                    based on the location contents of requests; and

         o "both" - meaning this locationValue is to be viewed by both
                    types of SIP entities.

      Not all SIP entities have to read the locationValue within a


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      Geolocation header, therefore a parameter value of "both" does
      not mean "every" SIP element receiving this request, it means all
      that care to pay attention to a locationValue.  The default
      behavior of SIP entities reading the locationValue is that if
      this header parameter is NOT present, the intended recipient is
      the destination UAS.

   Each locationValue MUST contain exactly one "inserted-by" parameter,
   indicating which SIP entity added the locationValue to the SIP
   request.

   Each of the three types of header parameters listed here MAY appear
   in any locationValue once.  There MUST NOT be more than one
   "inserted-by=" parameter or one "used-for-routing" parameter or one
   "recipient=" parameter in the same locationValue.  However, there
   can be more than one locationValue in the same Geolocation header.

   This document defines the Geolocation header as valid in the
   following SIP requests:

      INVITE [RFC3261],             REGISTER [RFC3261],
      OPTIONS [RFC3261],            BYE [RFC3261],
      UPDATE [RFC3311],             INFO [RFC2976],
      MESSAGE [RFC3428],            REFER [RFC3515],
      SUBSCRIBE [RFC3265],          NOTIFY [RFC3265],
      PUBLISH [RFC3903] and         PRACK [RFC3262]


   Discussing location using the PUBLISH Request Method is out of scope
   for this document, but the Table 1 shows PUBLISH is to support
   Location Conveyance via this extension.


   The following table extends the values in Table 2&3 of RFC 3261
   [RFC3261].

      Header field             where proxy INV ACK CAN BYE REG OPT PRA
      ----------------------------------------------------------------
      Geolocation              R     ar     o   -   -   o   o   o   o

      Header field             where proxy SUB NOT UPD MSG REF INF PUB
      ----------------------------------------------------------------
      Geolocation              R     ar     o   o   o   o   o   o   o

               Table 1: Summary of the Geolocation Header

   The Geolocation header field MAY be included in any one of the above
   requests by a UAC.  A proxy MAY add the Geolocation header, but MUST
   NOT modify any pre-existing locationValue, including its associated
   header parameters of within an existing Geolocation header value,
   unless one of the existing locationValues is used to retarget the
   request towards a new destination UAS.  This is discussed in section


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   5.3.

   [RFC3261] states message bodies cannot be added by proxies.
   Therefore, any Geolocation header field added by a proxy MUST be in
   the form of a location-by-reference URI, in its own locationValue
   header value.

   Adding a new locationValue to an existing Geolocation header SHOULD
   NOT occur without appropriate caution to the fact that Location
   Recipients might not understand how to process more than one
   location, given this document's limited guidance as to what a
   Location Recipient should do when receiving more than one location
   (i.e., currently no priority instructions are given for which
   locationValue to use if there are more than one).  A Location
   Recipient can easily be confused by too much location information,
   producing undesirable results.  The <tuple id> element in the
   PIDF-LO XML indicates whose location is contained in the PIDF-LO.

   Location Recipients receiving a location object, received directly
   or as the result of a dereference, MUST honor the usage element
   rules within that XML document, per RFC 4119.  Such entities MUST
   NOT alter the rule set.


3.3 424 (Bad Location Information) Response Code

   If a UAS or SIP intermediary detects an error in a request message
   specific to the location information supplied by-value or
   by-reference. The new 4XX level error is created here to indicate a
   problem with the location in the request message.  This document
   creates and IANA registers the new error code:

      424 (Bad Location Information)

   The 424 (Bad Location Information) response code is a rejection of
   the request, due to its location contents, indicating the location
   information was malformed or not satisfactory for the recipient's
   purpose, or could not be dereferenced.

   Section 3.4 creates the Geolocation-Error header to provide more
   detail about what was wrong with the location information in the
   request.  This header MUST be in the 424 response, containing a
   locationErrorValue for each invalid locationValue in the request
   (i.e., and one-for-one matching if all locationValues in the request
   were bad).

   If more than one location is present in a request (by-value or
   by-reference), and any of the locationValues is good for the
   Location Recipient to process, a 424 MUST NOT be sent.  The 424 is
   only appropriate when the Location Recipient needs a locationValue
   and there are no locationValues included in a SIP request that are
   usable by a recipient.


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   A 424 (Bad Location Information) response is a final response within
   a transaction, and does not terminate a dialog.

   The UAC can use whatever means it knows of to verify/refresh its
   location information before attempting a new request that includes
   location. There is no cross-transaction awareness expected by either
   the UAS or SIP intermediary as a result of this error message.

   The new 424 (Bad Location Information) error code is IANA registered
   in Section 8 of this document.  An initial set of location error of
   IANA registered Geolocation-Error codes are in Section 3.4 of this
   document.


3.4 The Geolocation-Error Header Providing Error Granularity

   As discussed in Section 3.3, more granular error notifications,
   specific to location errors within a received request, are required
   if the UAC is to know what was wrong within the original request.
   The Geolocation-Error header is created here for this purpose.
   Geolocation-Error header is used to convey location specific errors
   within a response.  Additions to this IANA registered header require
   an RFC be published.

   Geolocation-Error        = "Geolocation-Error" HCOLON
                               [locationErrorValue
                               *(COMMA locationErrorValue)]
   locationErrorValue       = location-error-code *(SEMI
                               location-error-params)
   location-error-code      = 1*3DIGIT
   location-error-params    = location-error-node-id
                              / DQOUTE location-error-host-id DQOUTE
                              / CAtype *(SEMI CAtype)
                              / DQOUTE location-error-code-text DQOUTE
                              / generic-param ; from RFC3261
   location-error-node-id   = "node" EQUAL hostname; from RFC3261
   location-error-host-id   = "inserter" EQUAL hostname ; from RFC3261
   CAtype                   = "CAtype" EQUAL civic-code *(SEMI "CAtype"
                                EQUAL civic-code)
   location-error-code-text = "code" EQUAL quoted-string ; from RFC3261
   civic-code               = IANA registered CAtypes; from
                                                      [IANA-civic]

   The Geolocation-Error header MUST contain at least one
   locationErrorValue to indicate what was wrong with the original
   locationValue in the corresponding request. If a Location Recipient
   experienced more than one error in the locationValue of the
   corresponding SIP request, there can be one locationErrorValue per
   problem with the locationValue in the request (the except to this is
   involving CAtypes, which will be covered later here).  If there was
   something wrong with more than one locationValue in a request, a


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   corresponding locationErrorValue would be sent, one per error, in
   the response.  Each locationErrorValue contains a 3-digit error code
   (defined in subsections to this section of this doc) indicating what
   was wrong with the location(s) in the request.  Each error type has
   a corresponding quoted error text string that is human
   understandable.

   Also within the locationErrorValue is the Location Recipient
   identifier (the "node=") who experienced the location error, as well
   as an identifier of which SIP entity (the "inserter=") the Location
   Recipient is told (in the locationValue) added the locationValue to
   this request.  The "node=" and "inserter=" are domain identifier of
   a SIP entity, the same as is entered in the "sent-by" parameter of
   the Via header for that entity [RFC3261].  As stated in section 18
   of RFC 3261, the usage of FQDN is RECOMMENDED.  Here are examples of
   both

      node=bob.example.com

      inserter=alice.example.com

   Both "node=" and "inserter=" parameters MUST be present in all
   locationErrorValues in a response, unless the "inserted-by="
   parameter was not in the request.  The "inserter=" parameter is
   copied from the "inserted-by=" parameter within the locationValue of
   the request.

   Here's why, a Location Recipient that experienced the location
   problem with the request needs to tell who added which location into
   the original request.  Since more than one SIP entity can insert
   location into a request, all other SIP elements may be confused by
   receiving this error header.  So, the header has to identify who it
   is for, so that all other SIP entities that read the header know to
   ignore it, since it is not for them.  This is of particular use if
   the original UAC did not include a locationValue in the original SIP
   request, but a SIP server along the path did insert a locationValue.
   The locationErrorValue would travel to each SIP entity along the
   original path and tell both the server that included the
   locationValue what was wrong with the location and the UAC who
   did not know what the error meant.

   A worse case is when both the original UAC and a SIP server along
   the path included a locationValue, but there was only something
   wrong with one of the locationValues.  Without this identification
   of which locationValue was in error, both entities would react and
   one would do so incorrectly.

   Finally, there can be a list of one or more CAtype civic-codes that
   are determined to be in error by the Location Recipient.  Perhaps
   the Location Recipient believes one or more CAtypes are missing, and
   required in order to fully process the locationValue in the request,
   or perhaps data entered in one or more CAtypes is wrong, according


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   to the Location Recipient.  The list of CAtypes is taken from those
   that are IANA registered at [IANA-civic].

   More than one locationErrorValue in a Geolocation-Error header is
   separated by a comma.

   If more than one locationErrorValue is in a response, and intended
   for the same "inserter=", the error codes SHOULD NOT conflict in
   meaning.  In other words, two error codes (within separate
   locationErrorValues of the same response) SHOULD NOT give misleading
   or inconsistent indications to the location "inserter=".

   Here is an example of a Geolocation-Error header

   Geolocation-Error: 106; "node=bob.example.com";
                           "inserter=alice.example.com";
                           CAtype=A3; CAtype=STS;
                           code="incomplete location supplied"

   In this example, the Location Recipient (node=Bob) has determined
   the location supplied by the "inserter=" (inserter=Alice) was not
   enough to determine where (Alice) was.  Specifically, Bob has
   determined that CAtypes A3 (the city) and STS (the street type
   (Street, Road, Avenue, etc)) were not present to form a complete
   location of the Alice.  A subsequent request by Alice that included
   these two additional pieces of location information would tell Bob
   where Alice was.

   Notice the CAtypes that were in error are (in the above example
   Geolocation-Error header), according to the Location Recipient,
   listed in the locationErrorValue.  The associated CAtype values MUST
   NOT be listed in the locationErrorValue.  This is for
   privacy/security concerns.  It is up to the Location Recipient to
   determine which CAtypes were in error, and only list those CAtypes
   in the response.  The "inserter=" entity MUST determine what to do
   about correcting each CAtype found in error for subsequent location
   conveyance.  Usually, this would involve either refreshing its
   location information however it learned its location in the first
   place, or merely listing what information is lacking/wrong to the
   location sender (i.e., the user) or its network management.

   The following table extends the values in Table 2&3 of RFC 3261
   [RFC3261].

      Header field             where proxy INV ACK CAN BYE REG OPT PRA
      ----------------------------------------------------------------
      Geolocation-Error         r     ar    o   -   -   o   o   o   o

      Header field             where proxy SUB NOT UPD MSG REF INF PUB
      ----------------------------------------------------------------
      Geolocation-Error         r     ar    o   o   o   o   o   o   o



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            Table 2: Summary of the Geolocation-Error Header

   The Geolocation-Error header field MAY be included in any response
   to one of the above SIP requests, so long as Geolocation was in the
   request part of the transaction.  The choice of which SIP requests
   are in table 2 above come from which Methods can optionally have the
   Geolocation header (see section 3.2).

   Here is an example of a transaction that has a location error.  In
   this case, Bob responds with a 424 (Bad Location Information)
   response, including a Geolocation-Error header, is in Figure 1.

          Alice                                     Bob
            |                                        |
            |       Request w/ Location              |
            |--------------------------------------->|
            |                                        |
            |                                        |
            |  424 (Bad Location Information)        |
            |  with Geolocation-Error containing     |
            |  106 (Incomplete Location Information) |
            |<---------------------------------------|
            |                                        |

   Figure 1. Basic Transaction with 424 and Geolocation-Error Header

   The following subsections provide an initial list of location
   specific granular codes for any SIP responses, including the new 424
   (Bad Location Information) response.  If more than one specific
   Geolocation-Error code is applicable for a response, each MUST be in
   the response.  Geolocation-Error Code 100 is the generic 'location
   was supplied, but not understood' error.  If a more specific code
   applies, a code 100 is unnecessary.


3.4.1  Geolocation-Error Code 100 Location Not Understood

   Geolocation-Error code 100 "Location Format not supported" means the
   location format supplied in the request, by-value or by-reference,
   was not supported.

   This code means the recipient understood that location was included
   in the message, but the format is not supported.  Perhaps the format
   was a freeform text format or data-URL and the recipient only
   understood location in RFC 4119 PIDF-LO format (civic or
   x.y(.z) coordinate). This error code applies when a recipient has
   difficulty parsing the location supplied in the request.

   If the format is understood, but not desired, an error code 101 or
   102 MUST be returned in a 424 response, depending on which location
   format is desired. The Location Recipient returns an error code 101
   or 102 when it only understands one location format (coordinate or


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   civic) and did not receive that format.

   If a more specific error code is appropriate in a response,
   including error code 100 is unnecessary.

   error-text-string: Location format not supported

   An example usage in a SIP 424 response:

   Geolocation-Error: 100; "node=bob.example.com";
                           "inserter=alice.example.com";
                           CAtype=A3; CAtype=STS;
                           code="Location Format not supported"


3.4.2  Geolocation-Error Code 101 Coordinate-location Format Desired

   Geolocation-Error code 101 "Coordinate-location Format Desired"
   means the location format supplied in the request (probably
   formatted in civic), by-value or by-reference, was understood and
   supported, but that the recipient, or an application on the
   recipient, can or prefers to only process location in the
   coordinate-location format.

   A typical reaction to receiving this code is to resend the
   original message with location formatted in coordinate instead.

   error-text-string: Coordinate-location Format Desired

   An example usage in a SIP 424 response:

   Geolocation-Error: 101; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Coordinate-location Format Desired"


3.4.3  Geolocation-Error Code 102 Civic-location Format Desired

   Geolocation-Error code 102 "Civic-location Format Desired" means the
   location format supplied in the request (probably formatted in
   coordinate), by-value or by-reference, was understood and supported,
   but that the recipient, or an application on the recipient, can or
   prefers to only process location in the civic-location format.

   A typical reaction to receiving this code is to resend the
   original message with location formatted in civic instead.

   error-text-string: Civic-location Format Desired

   An example usage in a SIP 424 response:




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   Geolocation-Error: 102; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Civic-location Format Desired"


3.4.4  Geolocation-Error Code 103 Cannot Parse Location Supplied

   Geolocation-Error code 103 "Cannot parse location supplied" means
   the location provided, whether by-value or by-reference, in a
   request is not well formed.

   error-text-string: Cannot parse location supplied

   An example usage in a SIP 424 response:

   Geolocation-Error: 103; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Cannot parse location supplied"

3.4.5  Geolocation-Error Code 104 Cannot Find Location Information

   Geolocation-Error code 104 "Cannot find location" means location was
   expected in the request, but the recipient cannot find it.

   This can be either because the cid: pointed to a message body part
   that is not present in the request, there was no location message
   body part, or what is dereferenced at the supplied locationURI did
   not return a PIDF-LO, or location is encrypted/opaque to the
   recipient.

   A typical reaction to receiving this code is for the location sender
   to verify that it has indeed included location information in the
   request in the properly indicated place and then to send the request
   again.

   error-text-string: Cannot find location

   An example usage in a SIP 424 response:

   Geolocation-Error: 104; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Cannot find location"


3.4.6  Geolocation-Error Code 105 Conflicting Locations Supplied

   Geolocation-Error code 105 "Conflicting Locations Supplied" means a
   Location Recipient received more than one location describing where
   the Target is, and is either unsure which whole location is true or
   which parts of multiple locations make up where the Target is.

   This is generally a case of either too much information, and the


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   information is pointing towards at least two different positions,
   confusing the recipient.

   A possible scenario exists in which at least two locations are in
   the request, perhaps one or more were added by proxies along the
   path of the request, each pointing to where the UAC is.  If these
   are pointing at different positions - the UAS does not know which to
   trust.  This error code unfortunately means the UAS cannot solve for
   which location needs to be ignored to make up a complete location,
   or how to prioritize one location over all others in the same
   request.

   A typical reaction to receiving this code is to reduce the number of
   different locations supplied in the request, if under control by the
   Target, and send another message to the Location Recipient.

   error-text-string: Conflicting Locations Supplied

   An example usage in a SIP 424 response:

   Geolocation-Error: 105; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Conflicting Locations Supplied"


3.4.7  Geolocation-Error Code 106 Incomplete Location Supplied

   Geolocation-Error code 106 "Incomplete Location Supplied" means
   there is not enough location information, by-value or retrieved
   by-reference, to determine where the location Target is.

   Perhaps the coordinate precision is not fine enough, or the civic
   address lacks the fields to inform the UAS or proxy where the Target
   is.  This might be true for request retargeting, or it might be true
   for first responder dispatch or pizza delivery (for example, because
   the street address is missing).

   A typical reaction to receiving this code is for the location sender
   to convey more (precise) location information, if doing so is
   allowed by local policy.

   error-text-string: Incomplete location supplied

   An example usage in a SIP 424 response:

   Geolocation-Error: 106; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Incomplete location supplied"






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3.4.8  Geolocation-Error Code 107 Cannot Dereference

   Geolocation-Error code 107 "Cannot dereference" means the act of
   dereferencing failed to return the Target's location.  This
   generally means the supplied URI is bad.

   error-text-string: Cannot dereference

   An example usage in a SIP 424 response:

   Geolocation-Error: 107; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Cannot dereference"


3.4.9  Geolocation-Error Code 108 Dereference Denied

   Geolocation-Error code 108 "Dereference Denied" means there was
   insufficient authorization to dereference the Target's location.

   error-text-string: Dereference Denied

   An example usage in a SIP 424 response:

   Geolocation-Error: 108; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Dereference Denied"


3.4.10 Geolocation-Error Code 109 Dereference Timeout

   Geolocation-Error code 109 "Dereference Timeout" means the
   dereferencing node has not received the Target's location within a
   reasonable timeframe.

   error-text-string: Dereference Timeout

   An example usage in a SIP 424 response:

   Geolocation-Error: 109; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Dereference Timeout"


3.4.11 Geolocation-Error Code 110 Cannot Process Dereference

   Geolocation-Error code 110 "Cannot process Dereference" means the
   dereference protocol has received an overload condition error,
   indicating the location cannot be accessed at this time.

   If a SIP or SIPS scheme were used to dereference the Target's
   location, and a 503 (Service Unavailable) were the response to the


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   dereference query, this Geolocation-Error code 11 would be placed in
   the 424 (Bad Location Information) response to the location sender.

   error-text-string: Cannot process Dereference

   An example usage in a SIP 424 response:

   Geolocation-Error: 110; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="Cannot process Dereference"


3.4.12  Geolocation-Error Code 120 Unsupported Scheme - SIP desired

   Geolocation-Error code 120 "Unsupported Scheme - SIP desired" means
   the location dereferencer cannot dereference using the
   location-by-reference URI scheme supplied because it does not
   support the necessary protocol to do this.

   This code means the Location Recipient can dereference the Target's
   location using a SIP-URI scheme.  There can be more than one
   locationErrorValue in a Geolocation-Error header, indicating in this
   context the recipient can dereference using each scheme protocol
   included in the Geolocation-Error header.

   Note that indicating SIP to be used to dereference location is
   requesting the transmission to be in cleartext, which is a security
   risk. Therefore, the SIP scheme SHOULD NOT be used to dereference.
   An exception can be made for emergency calling, preferably after
   SIPS has been attempted, and failed.

   A typical reaction to receiving this code would be for the location
   sender to send a URI with the sip scheme.

   error-text-string: unsupported scheme - SIP desired

   An example usage in a SIP 424 response:

   Geolocation-Error: 120; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="unsupported scheme - SIP desired"


3.4.13  Geolocation-Error Code 121 Unsupported Scheme - SIPS desired

   Geolocation-Error code 121 "Unsupported Scheme - SIPS desired" means
   the location dereferencer cannot dereference using the
   location-by-reference URI scheme supplied because it does not
   support the necessary protocol to do this.

   This code means the Location Recipient can dereference the Target's
   location using a SIPS-URI scheme.  There can be more than one


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   locationErrorValue in a Geolocation-Error header, indicating in this
   context the recipient can dereference using each scheme protocol
   included in the Geolocation-Error header.

   error-text-string: unsupported scheme - SIPS desired

   An example usage in a SIP 424 response:

   Geolocation-Error: 121; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="unsupported scheme - SIPS desired"


3.4.14  Geolocation-Error Code 122 Unsupported Scheme - pres desired

   Geolocation-Error code 122 "Unsupported Scheme - pres desired" means
   the location dereferencer cannot dereference using the
   location-by-reference URI scheme supplied because it does not
   support the necessary protocol to do this.

   This code means the Location Recipient can dereference the Target's
   location using a PRES-URI scheme.  There can be more than one
   locationErrorValue in a Geolocation-Error header, indicating in this
   context the recipient can dereference using each scheme protocol
   included in the Geolocation-Error header.

   error-text-string: unsupported scheme - pres desired

   An example usage in a SIP 424 response:

   Geolocation-Error: 122; "node=bob.example.com";
                           "inserter=alice.example.com";
                           code="unsupported scheme - pres desired"


3.5  The Geolocation Option Tag

   This document creates and IANA registers one new option tag:
   "geolocation".  This option tag is to be used, per RFC 3261, in the
   Require, Supported and Unsupported headers.  Whenever a UA wants to
   indicate support for this SIP extension, the geolocation option tag
   is included in a Supported header of the SIP message.

   Including the geolocation option-tag within an Unsupported header of
   a 420 (Bad Extension) response is appropriate when a UAS
   does not support this Geolocation extension.

   A UAC adding this option-tag to a Require header field indicates to
   a UAS the UAS MUST support this extension in order to continue
   processing the message, or send a 420 response back to the UAC.
   Some environments might use a Require header in this way, but it
   should be used with caution to prevent unnecessary communications


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   problems.

   A UAC SHOULD NOT include this option tag in a Proxy-Require header,
   since a UAC is not likely to understand the topology of the
   infrastructure, and therefore would not understand which proxy will
   do the location-based routing function, if any.  A potentially bad
   scenario would have the first proxy not support this extension, but
   a subsequent proxy does.  This would result in no communications
   past the first proxy, which MUST send the 420 back under these
   circumstances.

3.6 Using sip/sips/pres as a Dereference Scheme

   If a location-by-reference (LbyR) URI is included in a SIP request,
   it MUST be in a locationValue in the Geolocation header and it MUST
   be a SIP, SIPS or PRES-URI .  When PRES: is used, if the resulting
   resolution, per [RFC3856], resolves to a SIP: or SIPS: URI, this
   section applies.  Use of other protocols for dereferencing of a
   PRES: URI is not defined, and such use is subject to review against
   RFC 3693 Using Protocol criteria.

   Dereferencing a Target's location using SIP or SIPS MUST be
   accomplished by treating the URI as a presence URI and generating a
   SUBSCRIBE request to a presence server as per [RFC3856] using the
   'presence' event package.  The resulting NOTIFY will contain a PIDF,
   which MUST contain a PIDF-LO. See Figure 2. for a basic message flow
   for a dereference.

   When used in this manner, SIP is a Using Protocol per [RFC3693] and
   elements receiving location MUST honor the 'usage-element' rules as
   defined in this extension.

     Alice                 Location Server                      Bob
       |                                                         |
       |        INVITE w/ Location-by-Reference URI              |
       |-------------------------------------------------------->|
       |                          |                              |
       |                       200 (OK)                          |
       |<--------------------------------------------------------|
       |                          |                              |
       |                          |  SUBSCRIBE to LbyR URI       |
       |                          |<-----------------------------|
       |                          |  200 (OK)                    |
       |                          |----------------------------->|
       |                          |                              |
       |                          |  NOTIFY   w/ PIDF-LO         |
       |                          |----------------------------->|
       |                          |  200 (OK)                    |
       |                          |<-----------------------------|
       |                          |                              |

           Figure 2. Location-by-Reference and Dereferencing


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   In Figure 2., Alice sends Bob her location in a LbyR URI.  Bob
   receives this LbyR URI in the INVITE and generates a new transaction
   (SUBSCRIBE) to retrieve the PIDF-LO of Alice.  If accepted, the
   PIDF-LO will be in the NOTIFY request from the Location Server.
   This is the first instance between Alice and Bob that Alice's
   location is in any message, therefore it is sent only once, from the
   Location Server to Bob.

   A dereference of a location-by-reference URI using SUBSCRIBE is not
   violating a PIDF-LO 'retransmission-allowed' element value set to
   'no', as the NOTIFY is the only message in this multi-message set
   of transactions that contains the Target's location, with the
   location recipient being the only SIP element to receive location -
   which is the purpose of this extension: to convey location to a
   specific destination.


4. Geolocation Examples

   This section contains are two examples of messages providing
   location.  One shows location-by-value with coordinates, the other
   shows location-by-reference.  The example for (Coordinate format)
   is taken from [RFC3825]. A civic format example of the same position
   on the earth as is in the coordinate format example is in appendix
   B, which is taken from [RFC4776].  The differences between the two
   formats are within the <gp:location-info> of the examples.  Other
   than this portion of each PIDF-LO, the rest is the same for both
   location formats.

   The key to the provided samples is in the Geolocation header, which
   has a different type of URI, based on the different means of
   location conveyance.  Section 4.1 shows a "cid:" URI, indicating
   this SIP request contains a location-by-value message body - which
   is in the form of a PIDF-LO.  Section 4.2 shows a
   location-by-reference URI indicating location is to be acquired via
   an indirection dereference mechanism, which is determined by the
   scheme of URI supplied.


4.1 Location-by-value (Coordinate Format)

   This example shows an INVITE message with a coordinate, or
   coordinate location.  In this example, the SIP request uses a
   sips-URI  [RFC3261], meaning this message is TLS protected on a
   hop-by-hop basis all the way to Bob's domain.

   INVITE sips:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf9
   Max-Forwards: 70
   To: Bob <sips:bob@biloxi.example.com>
   From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl


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   Call-ID: 3848276298220188511@atlanta.example.com
   Geolocation: <cid:target123@atlanta.example.com>
     ;inserted-by=alice@atlanta.example.com ;recipient=endpoint
   Supported: geolocation
   Accept: application/sdp, application/pidf+xml
   CSeq: 31862 INVITE
   Contact: <sips:alice@atlanta.example.com>
   Content-Type: multipart/mixed; boundary=boundary1
   Content-Length: ...

   --boundary1

   Content-Type: application/sdp

   ...SDP goes here

   --boundary1

   Content-Type: application/pidf+xml
   Content-ID: alice123@atlanta.example.com

   <?xml version="1.0" encoding="UTF-8"?>
       <presence xmlns="urn:ietf:params:xml:ns:pidf"
          xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
          xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
          entity="pres:alice@atlanta.example.com">
        <tuple id="sg89ae">
         <timestamp>2007-12-02T14:00:00Z</timestamp>
         <status>
          <gp:geopriv>
            <gp:location-info>
              <gml:location>
                <gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
                  <gml:pos>33.001111 -96.68142</gml:pos>
                </gml:Point>
               </gml:location>
            </gp:location-info>
            <gp:usage-rules>
              <gp:retransmission-allowed>no</gp:retransmission-allowed>
              <gp:retention-expiry>2007-12-07T18:00:00Z</gp:retention-
                            expiry>
            </gp:usage-rules>
            <gp:method>DHCP</gp:method>
            <gp:provided-by>www.example.com</gp:provided-by>
          </gp:geopriv>
         </status>
        </tuple>
       </presence>
   --boundary1--

   The Geolocation header field from the above INVITE...



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      Geolocation: <cid:target123@atlanta.example.com>

   ...indicates the content-ID location [RFC2392] within the multipart
   message body of where location information is, with SDP being the
   other message body part.

   If the Geolocation header field were this instead:

      Geolocation: <sips:server5.atlanta.example.com/target123>

   ...this would indicate location by-reference was included in this
   message.  It is expected that any node wanting to know where user
   target123 is would subscribe to server5 to dereference the sips-URI.
   The returning NOTIFY would contain Alice's location in a PIDF-LO, as
   if it were included in a message body (part) of the original INVITE
   here.


4.2 Location-by-reference

   Below is an INVITE request with a location-by-reference URI instead
   of a location-by-value PIDF-LO message body part shown in Sections
   4.1.  It is up to the location recipient to dereference Alice's
   location at the Atlanta server containing the location record.
   Dereferencing, if done with SIP, is accomplished by the Location
   Recipient sending a SUBSCRIBE request to the URI reference for
   Alice's location.  The received NOTIFY is the first SIP message
   containing Alice's UA location, as a PIDF-LO message body.  The
   NOTIFY, in this case, is the SIP request that is conveying location,
   and not the INVITE.  There is no retransmission of location in this
   usage.

   INVITE sips:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/TLS pc33.atlanta.example.com
     ;branch=z9hG4bK74bf9
   Max-Forwards: 70
   To: Bob <sips:bob@biloxi.example.com>
   From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.example.com
   Geolocation: <sips:3sdefrhy2jj7@lis.atlanta.example.com>
     ;inserted-by=bigbox3.atlanta.example.com ;recipient=both
   Supported: geolocation
   Accept: application/sdp, application/pidf+xml
   CSeq: 31862 INVITE
   Contact: <sips:alice@pc33.atlanta.example.com>

   ...SDP goes here as the only message body

   A Location Recipient would need to dereference the sips-URI in the
   Geolocation header field to retrieve Alice's location.  If the
   atlanta.example.com domain chooses to implement location conveyance
   and delivery in this fashion (i.e., location-by-reference), it is


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   RECOMMENDED that entities outside this domain be able to reach the
   dereference server, otherwise this model of implementation is
   only viable within the atlanta.example.com domain.


5.  SIP Element Behavior

   Because a device's location is generally considered to be sensitive
   in nature, privacy of the location information needs to be protected
   when transmitting such information.  Section 26 of [RFC3261] defines
   the security functionality SIPS for transporting SIP messages with
   either TLS or IPSec, and S/MIME for encrypting message bodies from
   SIP intermediaries that would otherwise have access to reading the
   clear-text bodies.  SIP endpoints SHOULD implement S/MIME to encrypt
   the PIDF-LO message body (part) end-to-end when the Location
   Recipient is intended to be another UA.  The SIPS-URI from [RFC3261]
   MUST be implemented for message protection (message integrity and
   confidentiality) and SHOULD be used when S/MIME is not used.
   Possession of a dereferenceable location URI can be equivalent to
   possession of the location information itself and thus TLS SHOULD be
   used when transmitting location-by-reference hop-by-hop along the
   path to the Location Recipient.

   A PIDF includes identity information.  It is possible for the
   identity in the PIDF to be anonymous.  Implementations of this
   extension should consider the appropriateness of including an
   anonymous identity in the location information where a real identity
   is not required.  When using location-by-reference, it is
   RECOMMENDED that the URI does not contain any user identifying
   information (for example use 3fg5t5yqw@example.com rather than
   alice@example.com).

   Location Recipients MUST obey the privacy and security rules in the
   PIDF-LO as described in RFC 4119 regarding retransmission and
   retention.

   Self-signed certificates SHOULD NOT be used for protecting a PIDF,
   as the sender does not have a secure identity of the recipient.

   More than one location format (civic and coordinate) MAY be included
   in the same message body part, but all location parts of the same
   PIDF-LO MUST point at the same position on the earth.  The same
   location in multiple formats can allow the recipient to use the most
   convenient or preferable format for its use.  Multiple PIDF-LOs are
   allowed in the same request, with each allowed to point at separate
   positions - because each PIDF-LO has a Target identifier in it.
   Therefore, there will be no confusion by a Location Recipient
   receiving more than one PIDF-LO (in a message body or when
   dereferenced, or a combination).

   It is RECOMMENDED there is only one "location" in a single SIP
   Request for a given Target.  This means SIP servers SHOULD NOT add


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   another locationValue to a SIP request that already contains
   location.  This will likely lead to confusion at the ultimate
   location recipient because this extension does not provide guidance
   on what a recipient is to do with more than one location, nor does
   it give any preference regarding which location is better or worse
   than another location in the same request.

   It is allowed, but NOT RECOMMENDED, for more than one SIP element to
   insert location into a request along its path.  As described earlier
   in this document, each insertion of location into a SIP request is
   accompanied by a locationValue in a Geolocation header.  Also
   described earlier, each locationValue MUST contain an "inserted-by="
   value indicated to a Location Recipient which host inserted location
   into a particular request.


5.1 UAC Behavior

   A UAC can send location in a SIP request, because it is expected
   to facilitate location-based routing of the request, or
   spontaneously (i.e., a purpose not defined in this document but
   known to the UAC).

   A UAC conveying location MUST include a locationValue in a
   Geolocation header (see section 3.2) with either a location-by-value
   indication (a cid-URL), or a location-by-reference indication (a
   dereferenceable URI).  A location-by-value message body sent without
   a Geolocation header field MUST NOT occur.  The UAC supporting this
   extension MUST include a Supported header with the geolocation
   option tag.

   The geolocation option-tag is inserted in a Supported header by a
   UAC to provide an indication of support for this extension.  The
   presence of the geolocation option tag in a Supported header without
   a Geolocation header field in the same message informs a receiving
   SIP element the UAC understands this extension, but it does not know
   or wish to convey its location at this time.  Certain scenarios
   exist (location-based retargeting) in which location is required in
   a SIP request in order to retarget the message properly.  This
   affects how a UAS or SIP server processes to such a request.

   The geolocation option tag SHOULD NOT be used in the Proxy-Require
   Header, because the UAC often will not know the underlying topology
   to know which proxy will do the retargeting, thus increasing the
   likelihood of a request failure by the first hop proxy that does not
   understand this extension, but is required to by inclusion of the
   option-tag in this header.

   A UAC inserting a locationValue MUST include an "inserted-by="
   parameter to indicate its host-id.  This is copied to the
   "inserter=" parameter of the Geolocation-Error header in a response
   if there is something wrong with the location in the original


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   request.  Because more than one locationValue can be inserted along
   the path of the request, this indication is necessary to show which
   locationValue had the problem in the response.  For example:

   Geolocation: <cid:alice123@atlanta.example.com>;
                 inserted-by=alice@atlanta.example.com

   The UAC MAY include an intended target of this location parameter by
   adding the "recipient=" parameter to the locationValue like this:

   Geolocation: <cid:alice123@atlanta.example.com>;
                 inserted-by=alice@atlanta.example.com;
                 recipient=endpoint

   See section 3.2 for further details about all the header parameters
   of a locationValue.

   A UAC MAY SUBSCRIBE to a LbyR URI, using the 'presence' event
   package, for its own location.  The obvious reason for this is for
   the UAC to have its LbyV local to it.  This document does not give a
   reason why a UAC would want to do this.


5.1.1 UAC Receiving a Location Failure Indication

   If a sent request failed based on the location in the original
   request, a 424 (Bad Location Information) response is sent back to
   the UAC.  The 424 MUST have a Geolocation-Error header containing
   one or more locationErrorValues in the response message.  A
   locationErrorValue has a header parameter indicating which entity
   inserted the location pertaining to this error, called the
   "inserter=" parameter.  This "inserter=" parameter is copied from
   the "inserted-by=" parameter of the locationValue by the UAS or
   proxy sending the error response.  A UAC receiving this 424 should
   review this "inserter=" parameter in the locationErrorValue to see
   if it indicates this UAC.  If locationErrorValue does not, the
   locationErrorValue  should be ignored, and the response SHOULD be
   treated as a 4XX response.  If locationErrorValue does indicate this
   UAC, this UAC MUST process the response, including the
   Geolocation-Error code (defined in section 3.4).

   In addition to the error code, there MAY be a list of CAtypes in the
   locationErrorValue.  If there are any, these are what the UAS or
   proxy determined was wrong with the location contained in the
   original response.  The listed CAtypes will not contain the values
   sent by the UAC in the request.  This is for security/privacy
   reasons.

   The UAC SHOULD take correct steps to rectify future errors, based on
   the received error code and any CAtypes listed, to increase the
   probability of successful requests in the future.  A UAC MAY
   reattempt a new request if it believes it can correct the stated


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   failure in the Geolocation-Error header.

   Any UAC that inserted location into a request should be prepared to
   receive the Geolocation-Error header in any response, looking to
   determine if the header is meant for the UAC, and to react
   accordingly.

   If a UAC includes location in a request, and either the UAS does not
   determine errored location was critical to the transaction and
   accept the request, or the request failed for another reason than
   location, any response MAY contain a Geolocation-Error header
   containing a locationErrorValue with the details of the location
   error.


5.2 UAS Behavior

   If the Geolocation header field is present in a received SIP
   request, the type of URI contained in the locationValue will
   indicate if location has been conveyed by-value in a message body
   (part) or by-reference, requiring an additional dereference
   transaction.  If the by-reference URI is sip:, sips: or pres:, the
   UAS MUST initiate a SUBSCRIBE to the URI provided to retrieve the
   PIDF-LO being conveyed by the UAC per [RFC3856].  If successful, the
   PIDF-LO will be returned in the NOTIFY request from the remote host.

   A Require header with the geolocation option tag indicates the
   UAC is requiring the UAS understand this extension or else send
   an error response.  A 420 (Bad Extension) with a geolocation option
   tag in an Unsupported header would be the appropriate response in
   this case.

   It is possible, but undesirable, for a message to arrive with a body
   containing a location-by-value, but with no Geolocation header field
   value pointing to it (potentially no Geolocation header field at
   all). In this case, the recipient MAY still read and use the message
   body. Unless stated otherwise by future standards-track
   publications, a Location-by-reference URI only has meaning within
   the Geolocation header field and MUST NOT appear in any other SIP
   header field.

   There are 3 Geolocation header parameters,

   o "inserted-by="
   o "used-for-routing"
   o "recipient="

   The "inserted-by=" parameter informs a Location Recipient which SIP
   element added this locationValue to the SIP request.  This parameter
   is mandatory for each locationValue in the request.  The value in
   the "inserted-by=" parameter is copied into the "inserter="
   parameter in each locationErrorValue if there is an error in the


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   location to be reported back to the location sender.  See section
   5.2.1.

   The "used-for-routing" parameter is included in the locationValue if
   a SIP server used the location in the request to determine how to
   route or forward the message towards the ultimate destination.  If
   there are more than one locationValue in the Geolocation header, and
   it is possible that different locationValues were used to route the
   message at different times of this request's journey.  This is
   allowed, as it is consistent with the rule that anytime a message is
   routed based upon a locationValue, a "used-for-routing" parameter is
   added to the applicable locationValue.  This parameter should be
   present in each locationValue used along the path.

   More than one locationValue inserted in a request should be placed
   the order it was placed, and not rearranged.  This informs a
   Location Recipient which was the last locationValue in the message
   that was used to route the message.  This is for troubleshooting and
   management reasons.

   The "recipient=" header parameter allow recipients to infer the SIP
   entity type this locationValue is intended to be for.  The types are
   "endpoint", meaning the ultimate destination UAS; "routing-entity",
   meaning SIP servers; and "both" meaning this locationValue is to be
   viewed by both types of SIP entities.

   Individual header parameters in any received locationValue MUST NOT
   be modified or deleted in transit to the ultimate destination.

   A UAS MUST NOT send location in a response message, as there can be
   any number of issues/problems with receiving location, and the UAC
   or proxy servers cannot error a response.  Therefore, the UAS, if it
   wants to send a UAC its location, SHOULD do so in a new request in a
   separate transaction.  This document gives no guidance which SIP
   request to use.

   A UAS MAY include a geolocation option-tag in the Supported header
   of a response, indicating it does understand this extension, even if
   location was not in a request to the UAS.

   A UAS wishing to dereference a location-by-reference URI contained
   in a received request will use the 'presence' event package in a
   SUBSCRIBE request to the URI.  If accepted, the PIDF-LO will return
   to the UAS in a NOTIFY request.  If there are any errors during
   dereferencing, or in the PIDF-LO itself, the UAS will error the
   original request to the UAC with a locationErrorValue indicating
   what the UAS concluded was wrong with the location.  This is to
   include any dereferencing problems encountered.






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5.2.1 UAS Generating a Location Failure Indication

   If a received request conveys location, but the UAS has one or
   more problems with a locationValue in the request (to include while
   attempting to dereference the UAC's location), the UAS MUST indicate
   each problem experienced with the location in the request in a
   424 (Bad Location Information) response back to the inserting
   entity if the UAS wants to reject the request because of the
   location.  A Geolocation-Error header is how the UAS informs the UAC
   of a location-based error within the request.  Section 3.4 lists
   these errors, which are all IANA registered.

   Because this extension to SIP allows more than one locationValue in
   a Geolocation header, each from separate SIP entities, there
   needs to be a means of identifying which entity inserted a
   particular locationValue for single error response purposes.  This
   is further complicated because SIP sends a single rejection
   response, that in this case, needs to go to more than one entity,
   and be ignored by all other entities not identified in such a way as
   to not confuse other SIP entities.

   Each locationValue has an "inserted-by=" parameter identifying which
   SIP entity added this locationValue to the request.  This value is
   copied to the locationErrorValue "inserter=" parameter if one needs
   to be sent, thus identifying the intended target of this
   locationErrorValue.  This locationErrorValue is ignored by all other
   receivers of this SIP response.

   Each locationErrorValue can have more than one error code within it.
   Each locationErrorValue is destined for one "inserter=" entity.
   This gives a UAS one mechanism to tell each inserter what the
   Location Recipient concluded was wrong with what the inserter
   included (as far as location is concerned).  Therefore,

   o  there MUST be a locationErrorValue for each locationValue that
      was considered bad by the UAS to ensure each upstream location
      inserter understands which error code(s)is intended for them (and
      which to ignore).

   o  if the PIDF-LO (received by-value or after dereference) contains
      civic CAtypes that the Location Recipient considers malformed or
      bad, each CAtype SHOULD be listed in the locationErrorValue to
      inform the "inserter=" entity what specifically was wrong with
      the locationValue, in addition to the error code.  Without these
      details, the location inserter might not know what part was
      malformed or incomplete about the information supplied in the
      request.

   o  the CAtype values MUST NOT be sent along with the CAtype names
      listed in the locationErrorValue.  This is for privacy/security
      reasons.



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   o  there MUST NOT be more than one locationErrorValue in the
      response per locationValue in the request.

   o  there MUST NOT be more than one locationErrorValue in the
      response for the same locationValue in the request.

   o  there MUST NOT be a locationErrorValue in the response for a
      locationValue in the request that was not in error, according to
      the Location Recipient.

   Here is an example of a Geolocation-Error header

   Geolocation-Error: 106; "node=bob.example.com";
                           "inserter=alice.example.com";
                           CAtype=A3; CAtype=STS;
                           code="incomplete location supplied"

   See Section 3.4 for further rules about the Geolocation-Error header
   and the locationErrorValue.

   The Geolocation-Error header is permitted in any response.  For
   example, Bob can reply to Alice with a 486 because he's not willing
   to accept the call at this time, and inform Alice that the location
   contained in the request was bad in some way.  In this case, the 486
   would contain a Geolocation-Error header indicating the specific
   location error experienced

   If there is more than one locationValue in a request, and any one of
   them is valid (i.e., one contains enough information to not generate
   a 424 if that was the only location present in the request), all
   other locations MAY be ignored, and a 424 MUST NOT be sent because
   of these other locations in the request.  Another response MAY be
   sent, which includes a locationErrorValue.  This document says
   nothing about what a Location Recipient does with more than one
   'good' location in a request (i.e., which to choose to use).

   Further, more than one error code is allowed in the
   locationErrorValue - each having an "inserter=" parameter.  The
   error codes destined for the same inserter MUST NOT contradict the
   meaning of the problem the UAS had with a particular locationValue.

   A Geolocation-Error is permissible in a 200 OK response.  This means
   everything else in the request was acceptable, but the location was
   not for a given error code(s).  One exception to this set of rules
   is if a geolocation option-tag was in the Require header in the
   request.  This would necessitate a 424 response.


5.3 Proxy Behavior

   [RFC3261] states message bodies cannot be added by proxies.
   However, proxies are permitted to add a header to a request.  This


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   implies that a proxy can add a Geolocation locationValue with
   location-by-reference URI, but not location-by-value message body.
   However, if location is already in a SIP request, a SIP server
   SHOULD NOT add another instance of the UAC's location to the same
   request.  This will likely cause confusion at the Location Recipient
   as to which to use.  This document gives no guidance how a UAS is to
   deal with more than one location in a SIP request, other than the
   intended "recipient=" parameter, which has no integrity protection
   in transit.  If more than one locationValue states
   "recipient=endpoint", this document gives no guidance what the UAS
   is to do.

   A proxy is permitted to read any locationValue, and the associated
   body, if not S/MIME protected, in transit if present, and MUST use
   the  contents of the header field to make location-based retargeting
   decisions, if retargeting requests based on location is a function
   of that proxy.

   More than one Geolocation locationValue in a message is permitted,
   but can cause confusion at the recipient.  If a proxy chooses to add
   a locationValue to a Geolocation header, which would be a local
   policy decision, the new locationValue MUST be added to the end of
   the header (after previous locationValue(s)).  This is done to
   create an order of insertion of locationValues along the path.
   Proxies MUST NOT modify the order of locationValues in a geolocation
   header.

   A proxy wishing to dereference a location-by-reference URI contained
   in a received request will use the 'presence' event package in a
   SUBSCRIBE request to the URI.  If accepted, the PIDF-LO will return
   to the proxy in a NOTIFY request.  If there are any errors during
   dereferencing, or in the PIDF-LO itself, the proxy will error the
   original request to the UAC with a locationErrorValue indicating
   what the proxy concluded was wrong with the location.  This is to
   include any dereferencing problems encountered.


5.3.1 Proxy Behavior with Geolocation Header Parameters

   SIP servers MUST NOT delete any existing Geolocation locationValue
   (URI or header parameter) from a request.  A Geolocation
   locationValue (URI or header parameter) MAY only be modified to by
   adding a "used-for-routing" parameter to an existing locationValue,
   if the request was retargeted based on the location within that
   locationValue.  Further modification of this Geolocation header
   field MUST NOT occur.  For example, an existing Geolocation
   locationValue in a request of:

   Geolocation: <cid:alice123@atlanta.example.com>;
                 inserted-by=alice123@atlanta.example.com;

   can be modified by a proxy to add the "used-for-routing" parameter,


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   like this:

   Geolocation: <cid:alice123@atlanta.example.com>;
                 inserted-by=alice123@atlanta.example.com;
                 used-for-routing

   if this is the locationValue the proxy used to make a retargeting
   decision based upon, but make no other modification.

   A SIP server MAY add a new Geolocation locationValue to a SIP
   request.  The proxy SHOULD NOT insert a locationValue of the UAC
   unless it is reasonably certain it knows the actual location of the
   endpoint, for example, if it thoroughly understands the topology of
   the underlying access network and it can identify the device
   reliably (in the presence of, for example, NAT).

   A server adding a locationValue to an existing Geolocation header
   would look like:

 Geolocation: <cid:alice123@atlanta.example.com>;
               inserted-by=alice123@atlanta.example.com,
              <sips:3sdefrhy2jj7@lis1.atlanta.example.com>;
               inserted-by=lis1.atlanta.example.com;

   Notice the locationValue added by the proxy is last among
   locationValues.  This practice MUST be done for all added
   locationValues.

   If this request was then retargeted by an intermediary using the
   locationValue inserted by the server, the intermediary would add a
   "used-for-routing" parameter like this:

 Geolocation: <cid:alice123@atlanta.example.com>;
               inserted-by=alice123@atlanta.example.com,
              <sips:3sdefrhy2jj7@lis1.atlanta.example.com>;
               inserted-by=lis1.atlanta.example.com; used-for-routing

   It is conceivable that an initial routing decision is made on an
   one locationValue, and subsequently another routing decision is
   made on a different locationValue.  This retargeting decision can be
   made on a newly inserted locationValue.  While unusual, it can
   occur.  In such a case, proxies MUST NOT remove any existing
   "used-for-routing" header parameter.  In this instance, the SIP
   server retargeting based on another locationValue MUST add the
   "used-for-routing" header parameter to the locationValue used for
   retargeting by this server.  This will result in a Geolocation
   header looking as if it were retargeting more than once, which would
   be true - and is the desired outcome.






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5.3.2 Proxy Error Behavior for Sending or Receiving locationErrorValues

   For proxies that receive a SIP request that contains a location
   error, either in a contained message body or after the proxy does a
   dereference of the LbyR URI, all the rules applicable to a UAS apply
   here  (see Section 5.2.1.), since in this case, the proxy is
   considered a Location Recipient. Therefore, there is no reason to
   restate them here, and potentially have the two section be
   inconsistent.  The one thing to add is that a proxy does not need to
   examine location contained in a request. Section 5.2.1. only applies
   to proxies that are monitoring or policing location within requests
   (for whatever reason).

   If a proxy inserted a locationValue into a request, it SHOULD be
   ready to examine the response to that request, in case there is one
   or more location errors in the response.  To a great degree, this
   scenario has the proxy behaving as a UAC (see section 5.1.1.) that
   included a locationValue a request, which then receives an error to
   that locationValue.

   If there is one or more locationErrorValues in the response, the
   proxy SHOULD examine each "inserter=" parameter in each
   locationErrorValue - looking for one that identifies the proxy.  If
   one matches the proxy's "inserted-by" value, that locationErrorValue
   is for only that proxy. This locationErrorValue needs to be reviewed
   for each error code and CAtype contained in the value.  The proxy
   SHOULD attempt to correct for the error reported to it for future
   insertion of location into requests.  This document gives no
   guidance what the proxy should do to rectify the bad location
   information, but a future document MAY address this.


6.  Geopriv Privacy Considerations

   Transmitting location information is considered by most to be highly
   sensitive information, requiring protection from eavesdropping,
   tracking, and altering in transit.  [RFC3693] articulates rules to
   be followed by any protocol wishing to be considered a Geopriv
   "Using Protocol", specifying how a transport protocol meetings
   those rules.  This section describes how SIP as a Using Protocol
   meets those requirements.

   Quoting requirement #4 of [RFC3693]:

   "The Using Protocol has to obey the privacy and security
    instructions coded in the Location Object and in the
    corresponding Rules regarding the transmission and storage
    of the LO."

   This document requires that SIP entities sending or receiving
   location MUST obey such instructions.



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   Quoting requirement #5 of [RFC3693]:

   "The Using Protocol will typically facilitate that the keys
    associated with the credentials are transported to the
    respective parties, that is, key establishment is the
    responsibility of the Using Protocol."

   [RFC3261] and the documents it references define the key
   establishment mechanisms.

   Quoting requirement #6 of [RFC3693]:

   "(Single Message Transfer)  In particular, for tracking of
    small Target devices, the design should allow a single
    message/packet transmission of location as a complete
    transaction."

   When used for tracking, a simple NOTIFY or UPDATE normally is
   relatively small, although the PIDF itself can get large.  Normal
   RFC 3261 procedures of reverting to TCP when the MTU size is
   exceeded would be invoked.


7.  Security Considerations

   Conveyance of physical location of a UAC raises privacy concerns,
   and depending on use, there probably will be authentication and
   integrity concerns.  This document calls for conveyance to normally
   be accomplished through secure mechanisms, like S/MIME protecting
   message bodies (but this is not widely deployed) or TLS protecting
   the overall signaling.  In cases where a session set-up is
   retargeted based on the location of the UAC initiating the call or
   SIP MESSAGE, securing the by-value location with an end-to-end
   mechanism such as S/MIME is problematic, because one or more proxies
   on the path need the ability to read the location information to
   retarget the message to the appropriate new destination UAS.
   Securing the location hop-by-hop, using TLS, protects the message
   from eavesdropping and modification, but exposes the information to
   all proxies on the path as well as the endpoint.  In most cases, the
   UAC does not know the identity of the proxy or proxies providing
   location-based routing services, so that end-to-middle solutions
   might not be appropriate either.

   These same issues exist for basic SIP signaling, but SIP normally
   does not carry information to physically track a user; making this
   extension especially sensitive.

   When location is inserted by a UAC, which is RECOMMENDED, it can
   decide whether to reveal its location using hop-by-hop methods.  UAC
   implementations MUST make such capabilities conditional on explicit
   user permission, and SHOULD alert a user that location is being
   conveyed.  Proxies inserting location for location-based routing are


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   unable to meet this  requirement, and such use is NOT RECOMMENDED.
   Proxies conveying location using this extension MUST have the
   permission of the Target to do so.

   One facet within this extension is such that locations can be placed
   on a remote server, accessible with the possession of a URI.  The
   concept of a location-by-reference URI has its own security
   considerations.  It is tempting to assume that the dereference would
   have authentication, authorization and other security mechanisms
   that limit the access to information.  Unfortunately, this might not
   be true.  The access network the UAC is connected to can be the
   source of location reference, and it might not have any
   credentialing mechanism suitable for controlling access to location.
   Consider, specifically, a nomadic user connected to an access
   network in a hotel.  The UAC has no way to provide a credential
   acceptable to the hotel Location Server (LS) to any of its intended
   Location Recipients.  The recipient of a reference does not know if
   a reference has appropriate authorization policies or not.  The LS
   should provide location to any requestor.

   Accordingly, possession of the reference should be considered
   equivalent to possession of the value, and the reference should be
   treated with the same degree of care as the value.  Specifically,
   TLS MUST be used to protect the security of the reference.  Notice
   that this does not constrain the dereference protocol to use TLS.
   That specification is left entirely to the dereferencing protocol

   Because SIP servers can add location in transit, made more easy of
   the server is a Session Border Controller or B2BUA, this might cause
   there to be conflicting location information (error-code=6), which
   could be purposeful to error the request or just cause operation
   problems.  This problem might be inadvertent, compounded by the fact
   that there will likely be some SIP servers that add location on
   every call set-up.

   There is no integrity on any locationValue or locationErrorValue
   header parameter, so recipients of either header need to implicitly
   trust the header contents, and take whatever precautions each entity
   deems appropriate give these facts.


8.  IANA Considerations

   The following are the IANA considerations made by this SIP
   extension.  Modifications and additions to these registrations
   require a standards track RFC (Standards Action).

8.1 IANA Registration for the SIP Geolocation Header

   The SIP Geolocation header is created by this document, with its
   definition and rules in Section 3.2 of this document, to be added to
   the sip-parameters.


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   The Geolocation Header has the following header parameters to be
   Registered in a new table:

   Geolocation Header parameters

   Header Parameters     Parameter-values      Reference
   ----------------      ----------------      --------------
   recipient             endpoint              RFC XXXX (this document)
   recipient             routing-entity        RFC XXXX (this document)
   recipient             both                  RFC XXXX (this document)


8.2 IANA Registration for New SIP Option Tag

   The SIP option-tag "geolocation" is created by this document, with
   the definition and rule in Section 3.5 of this document, to be added
   to sip-parameters within IANA.


8.3 IANA Registration for Response Code 424

   Reference: RFC-XXXX (i.e., this document)
   Response code: 424 (recommended number to assign)
   Default reason phrase: Bad Location Information

   This SIP Response code is defined in section 3.3 of this document.


8.4 IANA Registration of New Geolocation-Error Header

   The SIP Geolocation-error header is created by this document, with
   its definition and rules in Section 3.4 of this document, to be
   added to the sip-parameters.


8.5 IANA Registration for the SIP Geolocation-Error Codes

   New location specific Geolocation-Error codes are created by this
   document, and registered in a new table at sip-parameters within
   IANA. Details of these error codes are in Section 3.4 of this
   document.

   Geolocation-Error codes
   -----------------------
   Geolocation-Error codes provide reason for the error discovered by
   Location Recipients, to place into SIP response messages to inform
   the location inserter of the error.

  Code Description                                          Reference
  ---- ---------------------------------------------------  ---------
  100  Location Format Not Supported: the location format   [this doc]


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       supplied in the request, by-value or by-reference,
       was not supported.

  101  Coordinate-location Format Desired: the location     [this doc]
       format supplied in the request was understood
       and supported, but that the recipient, or an
       application on the recipient, can or prefers to
       only process location in the coordinate-location
       format.

  102  Civic-location Format Desired: the location          [this doc]
       format supplied in the request was understood
       and supported, but that the recipient, or an
       application on the recipient, can or prefers to
       only process location in the civic-location
       format.

  103  Cannot Parse Location Supplied: the location         [this doc]
       provided, whether by-value or by-reference, in a
       request is not well formed.

  104  Cannot Find Location: the location was expected in   [this doc]
       the request, but the recipient cannot find it.

  105  Conflicting Locations Supplied: a Location Recipient [this doc]
       received more than one location describing where the
       Target is, and is either unsure which whole location
       is true or which parts of multiple locations make up
       where the Target is.

  106  Incomplete Location Supplied: there is not enough    [this doc]
       location information in the request to determine
       where the location Target is.

  107  Cannot Dereference: the act of dereferencing failed  [this doc]
       to return the Target's location.  This generally
       means the supplied URI is bad.

  108  Dereference Denied: there was insufficient           [this doc]
       authorization to dereference the Target's location.

  109  Dereference Timeout: the dereferencing node has not  [this doc]
       received the Target's location within a reasonable.
       timeframe

  110  Cannot Process Dereference: the dereference protocol [this doc]
       has received an overload condition error, indicating
       the location cannot be accessed at this time.

  120  Unsupported Scheme - sip desired: the location       [this doc]
       dereferencer cannot dereference using the
       location-by-reference URI scheme supplied, and


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       prefers a sip-uri.

  121 Unsupported Scheme - sips desired: the location       [this doc]
       dereferencer cannot dereference using the
       location-by-reference URI scheme supplied, and
       prefers a sips-uri.

  122 Unsupported Scheme - pres desired: the location       [this doc]
       dereferencer cannot dereference using the
       location-by-reference URI scheme supplied, and
       prefers a pres-uri.


9.  Acknowledgements

   To Dave Oran for helping to shape this idea. To Jon Peterson and
   Dean Willis on guidance of the effort. To Allison Mankin, Dick
   Knight, Hannes Tschofenig, Henning Schulzrinne, James Winterbottom,
   Jeroen van Bemmel, Jean-Francois Mule, Jonathan Rosenberg, Keith
   Drage, Marc Linsner, Martin Thomson, Mike Hammer, Paul Kyzivat,
   Shida Shubert, Umesh Sharma, Richard Barnes, Ted Hardie and Matt
   Lepinski for constructive feedback.  A special thanks to Dan Wing
   for help with the S/MIME example, and to Robert Sparks for many
   helpful comments and the proper building of the Geolocation-Error
   header.


10. References

10.1 References - Normative

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

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

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

 [RFC2392] E. Levinson, " Content-ID and Message-ID Uniform Resource
           Locators", RFC 2393, August 1998

 [RFC3863] H. Sugano, S. Fujimoto, G. Klyne, A. Bateman, W. Carr, J.
           Peterson, "Presence Information Data Format (PIDF)", RFC
           3863, August 2004

 [RFC3856] J. Rosenberg, " A Presence Event Package for the Session
           Initiation Protocol (SIP)", RFC 3856, August 2004




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 [RFC3859] J. Peterson, "Common Profile for Presence (CPP)", RFC 3859,
           August 2004

 [RFC3428] B. Campbell, Ed., J. Rosenberg, H. Schulzrinne, C. Huitema,
           D. Gurle, "Session Initiation Protocol (SIP) Extension for
           Instant Messaging" , RFC 3428, December 2002

 [RFC3311] J. Rosenberg, "The Session Initiation Protocol (SIP) UPDATE
           Method", RFC 3311, October 2002

 [RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
           Event Notification", RFC 3265, June 2002.

 [RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of
           Provisional Responses in Session Initiation Protocol (SIP)",
           RFC 3262, June 2002.

 [IANA-civic] http://www.iana.org/assignments/civic-address-types-
                     registry



10.2 References - Informative

 [RFC3693] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk,
           "Geopriv Requirements", RFC 3693, February 2004

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

 [RFC4776] H. Schulzrinne, " Dynamic Host Configuration Protocol
           (DHCPv4 and DHCPv6) Option for Civic Addresses Configuration
           Information ", draft-ietf-geopriv-dhcp-civil-09, "work in
           progress", January 2006


   Author Information

   James Polk
   Cisco Systems
   3913 Treemont Circle                              33.00111N
   Colleyville, Texas  76034                         96.68142W

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


   Brian Rosen
   NeuStar, Inc.
   470 Conrad Dr.                                    40.70497N
   Mars, PA  16046                                   80.01252W


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   US

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


Appendix A.  Requirements for SIP Location Conveyance

   The following subsections address the requirements placed on the
   UAC, the UAS, as well as SIP proxies when conveying location. There
   is a motivational statement below each requirements that is not
   obvious in intent

A.1 Requirements for a UAC Conveying Location

   UAC-1  The SIP INVITE Method [RFC3261] must support location
          conveyance.

   UAC-2  The SIP MESSAGE method [RFC3428] must support location
          conveyance.

   UAC-3  SIP Requests within a dialog should support location
          conveyance.

   UAC-4  Other SIP Requests may support location conveyance.

   UAC-5  There must be one, mandatory to implement means of
          transmitting location confidentially.

   Motivation:  interoperability

   UAC-6  It must be possible for a UAC to update location conveyed
          at any time in a dialog, including during dialog
          establishment.

   Motivation: in case a UAC has moved prior to the establishment of a
          dialog between UAs, the UAC must be able to send new location
          information.  In the case of location having been conveyed,
          and the UA moves, it needs a means to update the conveyed to
          party of this location change.

   UAC-7  The privacy and security rules established within [RFC3693]
          that would categorize SIP as a 'Using Protocol' must be met.

   UAC-8  The PIDF-LO [RFC 4119] is a mandatory to implement format for
          location conveyance within SIP, whether included by-value or
          by-reference.

   Motivation:  interoperability with other IETF location protocols and
          mechanisms

   UAC-9  There must be a mechanism for the UAC to request the UAS send


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          its location

          UAC-9 has been DEPRECATED by the SIP WG, due to the many
          problems this requirement would have caused if implemented.
          The solution is for the above UAS to send a new request to
          the original UAC with the UAS's location.

   UAC-10 There must be a mechanism to differentiate the ability of the
          UAC to convey location from the UACs lack of knowledge of its
          location

   Motivation: Failure to receive location when it is expected can be
          because the UAC does not implement this extension, or it can
          be that the UAC implements the extension, but does not know
          where it is.  This may be, for example, due to the failure of
          the access network to provide a location acquisition
          mechanisms the UAC understands.  These cases must be
          differentiated.


   UAC-11  It must be possible to convey location to proxy servers
          along the path.

   Motivation:  Location-based routing.


A.2 Requirements for a UAS Receiving Location

   The following are the requirements for location conveyance by a UAS:

   UAS-1  SIP Responses must support location conveyance.

          Just as with UAC-9, UAS-1 has been DEPRECATED by the SIP WG,
          due to the many problems this requirement would have caused
          if implemented. The solution is for the above UAS to send a
          new request to the original UAC with the UAS's location.

   UAS-2  There must be a unique 4XX response informing the UAC it did
          not provide applicable location information.

   In addition, requirements UAC-5, 6, 7 and 8 apply to the UAS


A.3 Requirements for SIP Proxies and Intermediaries

   The following are the requirements for location conveyance by a SIP
   proxies and intermediaries:

   Proxy-1  Proxy servers must be capable of adding a Location header
            field during processing of SIP requests.

   Motivation:  Provide the capability of network assertion of location


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            when UACs are unable to do so, or when network assertion is
            more reliable than UAC assertion of location

   Note: Because UACs connected to sip signaling networks may have
         widely varying access network arrangements, including VPN
         tunnels and roaming mechanisms, it may be difficult for a
         network to reliably know the location of the endpoint.  Proxy
         assertion of location is NOT RECOMMENDED unless the sip
         signaling network has reliable knowledge of the actual
         location of the Targets.

   Proxy-2  There must be a unique 4XX response informing the UAC it
            did not provide applicable location information.

Appendix B. Example of INVITE with S/MIME encrypted Civic PIDF-LO

   This appendix gives an *EXAMPLE* (meaning this might contain errors
   based on future review) of a SIP INVITE request that points to the
   same position on the earth as the coordinate based example that's in
   section 4.1 in the body of this document:

   The INVITE request is TLS hop-by-hop encrypted, and the
   location-by-value message body is S/MIME encrypted. This example
   shows the location message body in its unencrypted form for clarity.
   The message body lines below that have the '$' signs are S/MIME
   encrypted.  In this example, the SDP is not S/MIME encrypted.

   INVITE sips:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/TLS pc33.atlanta.example.com
     ;branch=z9hG4bK74bf9
   Max-Forwards: 70
   To: Bob <sips:bob@biloxi.example.com>
   From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.example.com
   Geolocation: <cid:alice123@atlanta.example.com>
     ;inserted-by=alice@atlanta.example.com ;recipient=endpoint
   Supported: geolocation
   Accept: application/sdp, application/pidf+xml
   CSeq: 31862 INVITE
   Contact: <sips:alice@pc33.atlanta.example.com>
   Content-Type: multipart/mixed; boundary=boundary1
   Content-Length: ...

   --boundary1

   Content-Type: application/sdp

   ...SDP goes here

   --boundary1

   Content-Type: application/pkcs7-mime;


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      smime-type=enveloped-data; name=smime.p7m
   Content-ID: alice123@atlanta.example.com

$  Content-Type: application/pidf+xml
$
$  <?xml version="1.0" encoding="UTF-8"?>
$     <presence xmlns="urn:ietf:params:xml:ns:pidf"
$         xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
$         xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
$         entity="pres:alice@atlanta.example.com">
$       <tuple id="sg89ae">
$        <timestamp>2007-07-09T14:00:00Z</timestamp>
$        <status>
$         <gp:geopriv>
$           <gp:location-info>
$             <cl:civicAddress>
$               <cl:country>US</cl:country>
$               <cl:A1>Texas</cl:A1>
$               <cl:A3>Colleyville</cl:A3>
$               <cl:HNO>3913</cl:HNO>
$               <cl:A6>Treemont</cl:A6>
$               <cl:STS>Circle</cl:STS>
$               <cl:PC>76034</cl:PC>
$               <cl:NAM>Haley's Place</cl:NAM>
$               <cl:FLR>1</cl:FLR>
$             <cl:civicAddress>
$           </gp:location-info>
$           <gp:usage-rules>
$             <gp:retransmission-allowed>no</gp:retransmission-allowed>
$             <gp:retention-expiry>2007-07-27T18:00:00Z</gp:retention-
$                           expiry>
$           </gp:usage-rules>
$           <gp:method>DHCP</gp:method>
$           <gp:provided-by>www.example.com</gp:provided-by>
$         </gp:geopriv>
$        </status>
$       </tuple>
$      </presence>
   --boundary1--


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   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE


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   IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
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