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Versions: (draft-ietf-sip-location-conveyance) 00 01 02 03 04 05 06 07 08 09 RFC 6442

Network Working Group                                        James Polk
Internet Draft                                            Cisco Systems
Expires: Mar 4, 2012                                       Brian Rosen
Intended Status: Standards Track (PS)                      Jon Peterson
                                                                NeuStar
                                                           Sept 4, 2011

         Location Conveyance for the Session Initiation Protocol
              draft-ietf-sipcore-location-conveyance-09.txt


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 SIP extension covers
   end-to-end conveyance as well as location-based routing, where SIP
   intermediaries make routing decisions based upon the location of the
   Location Target.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on Mar 4, 2012.


Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of


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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document.  Code Components extracted from this
   document must include Simplified BSD License text as described in
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   This document may contain material from IETF Documents or IETF
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   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.


Table of Contents

   1.  Conventions and Terminology used in this document . . . . . .  3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview of SIP Location Conveyance . . . . . . . . . . . . .  4
       3.1 Location Conveyed by Value  . . . . . . . . . . . . . . .  4
       3.2 Location Conveyed as a Location URI . . . . . . . . . . .  5
       3.3 Location Conveyed though a SIP Intermediary . . . . . . .  5
       3.4 SIP Intermediary Replacing Bad Location . . . . . . . . .  7
   4.  SIP Modifications for Geolocation Conveyance  . . . . . . . .  8
       4.1 The Geolocation Header Field  . . . . . . . . . . . . . .  8
       4.2 The Geolocation-Routing Header Field  . . . . . . . . . . 10
       4.2.1 Explaining Geolocation-Routing header-value States  . . 11
       4.3 424 (Bad Location Information) Response Code  . . . . . . 13
       4.4 The Geolocation-Error Header Field  . . . . . . . . . . . 14
       4.5 Location URIs in Message Bodies . . . . . . . . . . . . . 17
       4.6 Location Profile Negotiation  . . . . . . . . . . . . . . 17
   5.  Geolocation Examples  . . . . . . . . . . . . . . . . . . . . 18
       5.1 Location-by-value (Coordinate Format) . . . . . . . . . . 18
       5.2 Two Locations Composed in Same Location Object Example  . 20
   6.  Geopriv Privacy Considerations  . . . . . . . . . . . . . . . 22
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . 22
   8.  IANA Considerations   . . . . . . . . . . . . . . . . . . . . 24
       8.1 IANA Registration for New SIP Geolocation Header Field  . 24
       8.2 IANA Registration for New SIP Geolocation-Routing Header
           Field . . . . . . . . . . . . . . . . . . . . . . . . . . 24
       8.3 IANA Registration for New SIP Option Tags . . . . . . . . 25
       8.4 IANA Registration for New 424 Response Code . . . . . . . 25
       8.5 IANA Registration for New SIP Geolocation-Error Header
           Field . . . . . . . . . . . . . . . . . . . . . . . . . . 26
       8.6 IANA Registration for New SIP Geolocation-Error Codes . . 26
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 27


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   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . 27
       10.1 Normative References   . . . . . . . . . . . . . . . . . 27
       10.2 Informative References . . . . . . . . . . . . . . . . . 28
       Author Information  . . . . . . . . . . . . . . . . . . . . . 29
       Appendix A. Requirements for SIP Location Conveyance  . . . . 29


1.  Conventions and Terminology 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]. This document furthermore uses numerous terms defined
   in RFC 3693 [RFC3693], including Location Object, Location
   Recipient, Location Server, Target, Rulemaker and Using Protocol.

2.  Introduction

   Session Initiation Protocol (SIP) [RFC3261] creates, modifies and
   terminates multimedia sessions.  SIP carries certain information
   related to a session while establishing or maintaining calls.  This
   document defines how SIP conveys geographic location information of
   a Target to a Location Recipient (LR). SIP acts as a Using Protocol
   of location information, as defined in RFC 3693.

   In order to convey location information, this document specifies
   three new SIP header fields, Geolocation, Geolocation-Routing and
   Geolocation-Error, which carry a reference to a Location Object
   (LO), grant permission to route a SIP request based on the
   location-value and provide error notifications specific to location
   errors respectively. The Location Object (LO) may appear in a MIME
   body attached to the SIP request, or it may be a remote resource in
   the network.

   A Target is an entity whose location is being conveyed, per RFC
   3693. Thus, a Target could be a SIP user agent (UA), some other IP
   device (a router or a PC) that does not have a SIP stack, a non-IP
   device (a person or a black phone) or even a non-communications
   device (a building or store front). In no way does this document
   assume that the SIP user agent client which sends a request
   containing a location object is necessarily the Target. The location
   of a Target conveyed within SIP typically corresponds to that of a
   device controlled by the Target, for example, a mobile phone, but
   such devices can be separated from their owners, and moreover, in
   some cases the user agent may not know its own location.

   In the SIP context, a location recipient will most likely be a SIP
   UA, but due to the mediated nature of SIP architectures, location
   information conveyed by a single SIP request may have multiple
   recipients, as any SIP proxy server in the signaling path that
   inspects the location of the Target must also be considered a
   Location Recipient. In presence-like architectures, an intermediary


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   that receives publications of location information and distributes
   them to watchers acts as a Location Server per RFC 3693. This
   location conveyance mechanism can also be used to deliver URIs
   pointing to such Location Servers where prospective Location
   Recipients can request Location Objects.


3.  Overview of SIP Location Conveyance

   An operational overview of SIP location conveyance can be shown in 4
   basic diagrams, with most applications falling under one of the
   following basic use cases. Each is separated into its own subsection
   here in section 3.

   Each diagram has Alice and Bob as UAs. Alice is the Target, and Bob
   is an LR.  A SIP intermediary appears in some of the diagrams. Any
   SIP entity that receives and inspects location information is an LR,
   therefore in any of the diagrams the SIP intermediary that receives
   a SIP request is potentially an LR - though that does not mean such
   an intermediary necessarily has to route the SIP request based on
   the location information.  In some use cases, location information
   passes through the LS on the right of each diagram.


3.1 Location Conveyed by Value

   We start with the simplest diagram of Location Conveyance, Alice to
   Bob, where no other layer 7 entities are involved.

      Alice          SIP Intermediary       Bob               LS
        |                |                   |                 |
        |       Request w/Location           |                 |
        |----------------------------------->|                 |
        |                                    |                 |
        |             Response               |                 |
        |<-----------------------------------|                 |
        |                |                   |                 |

        Figure 1. Location Conveyed by Value

   In Figure 1, Alice is both the Target and the LS that is conveying
   her location directly to Bob, who acts as an LR. This conveyance is
   point-to-point - it does not pass through any SIP-layer
   intermediary.  A Location Object appears by-value in the initial SIP
   request as a MIME body, and Bob responds to that SIP request as
   appropriate.  There is a 'Bad Location Information' response code
   introduced within this document to specifically inform Alice if she
   conveys bad location to Bob (e.g., Bob "cannot parse the location
   provided", or "there is not enough location information to determine
   where Alice is").




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3.2 Location Conveyed as a Location URI

   Here we make Figure 1 a little more complicated by showing a
   diagram of indirect Location Conveyance from Alice to Bob, where
   Bob's entity has to retrieve the location object from a 3rd party
   server.


      Alice          SIP Intermediary       Bob               LS
        |                |                   |                 |
        |      Request w/Location URI        |                 |
        |----------------------------------->|                 |
        |                                    |    Dereference  |
        |                                    |        Request  |
        |                                   (To: Location URI) |
        |                                    |---------------->|
        |                                    |                 |
        |                                    |    Dereference  |
        |                                    |       Response  |
        |                                  (includes location) |
        |                                    |<----------------|
        |             Response               |                 |
        |<-----------------------------------|                 |
        |                |                   |                 |

        Figure 2. Location Conveyed as a Location URI

   In Figure 2, location is conveyed indirectly, via a Location URI
   carried in the SIP request (more of those details later).  If Alice
   sends Bob this Location URI, Bob will need to dereference the URI -
   analogous to Content Indirection [RFC4483] - in order to request the
   location information. In general, the LS provides the location value
   to Bob instead of Alice directly for conveyance to Bob.  From a user
   interface perspective, Bob the user won't know that this information
   was gathered from an LS indirectly rather than culled from the SIP
   request, and practically this does not impact the operation of
   location-based applications.

   The example given in this section is only illustrative, not
   normative. In particular, applications can choose to dereference a
   location URI at any time, possibly several times, or potentially not
   at all. Applications receiving a Location URI in a SIP transaction
   need to be mindful of timers used by different transactions. In
   particular, if the means of dereferencing the Location URI might
   take longer than the SIP transaction timeout (Timer C for INVITE
   transactions, Timer F for non-INVITE transactions), then it needs to
   rely on mechanisms other than the transaction's response code to
   convey location errors, if returning such errors are necessary.


3.3 Location Conveyed though a SIP Intermediary



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   In Figure 3, we introduce the idea of a SIP intermediary into the
   example to illustrate the role of proxying in the location
   architecture. This intermediary can be a SIP proxy or it can be
   a back-to-back-user-agent (B2BUA).  In this message flow, the SIP
   intermediary could act as a LR, in addition to Bob. The primary use
   case for intermediaries consuming location information is
   location-based routing. In this case, the intermediary chooses a
   next hop for the SIP request by consulting a specialized location
   service which selects forwarding destinations based on geographical
   location.

      Alice          SIP Intermediary       Bob               LS
        |                |                   |                 |
        |   Request      |                   |                 |
        |    w/Location  |                   |                 |
        |--------------->|                   |                 |
        |                |  Request          |                 |
        |                |   w/Location      |                 |
        |                |------------------>|                 |
        |                |                   |                 |
        |                |   Response        |                 |
        |                |<------------------|                 |
        |     Response   |                   |                 |
        |<---------------|                   |                 |
        |                |                   |                 |

        Figure 3. Location Conveyed though a SIP Intermediary

   However, the most common case will be one in which the SIP
   intermediary receives a request with location information (conveyed
   either by-value or by-reference) and does not know or care about
   Alice's location, or support this extension, and merely passes it on
   to Bob. In this case, the intermediary does not act as a Location
   Recipient.  When the intermediary is not an LR, this use case is the
   same as the one described in Section 3.1.

   Note that an intermediary does not have to perform location-based
   routing in order to be a Location Recipient. It could be the case
   that a SIP intermediary which does not perform location-based
   routing does care when Alice includes her location; for example,
   it could care that the location information is complete or that it
   correctly identifies where Alice is. The best example of this is
   intermediaries that verify location information for emergency
   calling, but it could also be for any location based routing - e.g.,
   contacting your favorite local pizza delivery service, making sure
 that organization has Alice's proper location in the initial SIP
 request.

   There is another scenario in which the SIP intermediary cares about
   location and is not an LR, one in which the intermediary inserts
   another location of the Target, Alice in this case, into the
   request, and forwards it.  This secondary insertion is generally not


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   advisable because downstream SIP entities will not be given any
   guidance about which location to believe is better, more reliable,
   less prone to error, more granular, worse than the other location or
   just plain wrong.

   This document takes a "you break it, you bought it" approach to
   dealing with second locations placed into a SIP request by an
   intermediary entity. That entity becomes completely responsible for
   all location within that SIP request (more on this in Section 4).


3.4 SIP Intermediary Replacing Bad Location

   If the SIP intermediary rejects the message due to unsuitable
   location information, the SIP response will indicate there was 'Bad
   Location Information' in the SIP request, and provide a location
   specific error code indicating what Alice needs to do to send an
   acceptable request (see Figure 4 for this scenario).

      Alice          SIP Intermediary       Bob               LS
        |                |                   |                 |
        |   Request      |                   |                 |
        |    w/Location  |                   |                 |
        |--------------->|                   |                 |
        |                |                   |                 |
        |   Rejected     |                   |                 |
        | w/New Location |                   |                 |
        |<---------------|                   |                 |
        |                |                   |                 |
        |   Request      |                   |                 |
        | w/New Location |                   |                 |
        |--------------->|                   |                 |
        |                |    Request        |                 |
        |                |  w/New Location   |                 |
        |                |------------------>|                 |
        |                |                   |                 |

        Figure 4. SIP Intermediary Replacing Bad Location

   In this last use case, the SIP intermediary wishes to include a
   Location Object indicating where it understands Alice to be. Thus,
   it needs to inform her user agent what location it will include in
   any subsequent SIP request that contains her location. In this
   case, the intermediary can reject Alice's request and, through the
   SIP response, convey to her the best way to repair the request in
   order for the intermediary to accept it.

   Overriding location information provided by the user requires a
   deployment where an intermediary necessarily knows better than an
   end user - after all, it could be that Alice has an on-board GPS,
   and the SIP intermediary only knows her nearest cell tower. Which is
   more accurate location information? Currently, there is no way to


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   tell which entity is more accurate, or which is wrong - for that
   matter.  This document will not specify how to indicate which
   location is more accurate than another.

   As an aside, it is not envisioned that any SIP-based emergency
   services request (i.e., IP-911, or 112 type of call attempt) will
   receive a corrective 'Bad Location Information' response from an
   intermediary.  Most likely, the SIP intermediary would in that
   scenario act as a B2BUA and insert into the request by-value any
   appropriate location information for the benefit of Public Safety
   Answering Point (PSAP) call centers to expedite call reception by
   the emergency services personnel; thereby, minimizing any delay in
   call establishment time. The implementation of these specialized
   deployments is, however, outside the scope of this document.


4.  SIP Extensions for Geolocation Conveyance

   The following sections detail the extensions to SIP for location
   conveyance.

4.1 The Geolocation Header Field

   This document defines "Geolocation" as a new SIP header field
   registered by IANA, with the following ABNF [RFC5234]:

   message-header    /= Geolocation-header ; (message-header from 3261)
   Geolocation-header = "Geolocation" HCOLON locationValue
                        *( COMMA locationValue )
   locationValue      =  LAQUOT locationURI RAQUOT
                          *(SEMI geoloc-param)
   locationURI        =  sip-URI / sips-URI / pres-URI
                          / http-URI / https-URI
                          / cid-url ; (from RFC 2392)
                          / absoluteURI ; (from RFC 3261)
   geoloc-param       =  generic-param;  (from RFC 3261)

   HCOLON, COMMA, LAQUOT, RAQUOT, and SEMI are defined in RFC3261
   [RFC3261].

   sip-URI, sips-URI and absoluteURI are defined according to [RFC3261].

   The pres-URI is defined in [RFC3859].

   http-URI and https-URI are defined according to [RFC2616] and
   [RFC2818], respectively.

   The cid-url is defined in [RFC2392] to locate message body parts.
   This URI type is present in a SIP request when location is conveyed
   as a MIME body in the SIP message.

   GEO-URIs [RFC5870] are not appropriate for usage in the SIP


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   Geolocation header, because it does not include retention and
   re-transmission flags as part of the location information. Other URI
   schemes used in the location URI MUST be reviewed against the RFC
   3693 [RFC3693] criteria for a Using Protocol. Section 4.6 discusses
   how URI schemes are communicated using this SIP extension, and what
   to do if a URI scheme is received that cannot be supported.

   The generic-param in the definition of locationValue is included as
   a mechanism for future extensions that might require parameters.
   This document defines no parameters for use with locationValue. If a
   Geolocation header field is received that contains generic-params,
   each parameter SHOULD be ignored, and SHOULD NOT be removed when
   forwarding the locationValue. If a need arises to define parameters
   for use with locationValue, a revision/extension to this document is
   required.

   The Geolocation header field MUST have at least one locationValue.
   A SIP intermediary SHOULD NOT add location to a SIP request that
   already contains location. This will quite often lead to confusion
   within LRs. However, if a SIP intermediary adds location, even if
   location was not previously present in a SIP request, that SIP
   intermediary is fully responsible for addressing the concerns of any
   424 (Bad Location Information) SIP response it receives about this
   location addition, and MUST NOT pass on (upstream) the 424 response.
   A SIP intermediary that adds a locationValue MUST position the new
   locationValue as the last locationValue within the Geolocation
   header field of the SIP request.

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

      INVITE [RFC3261],             REGISTER [RFC3261],
      OPTIONS [RFC3261],            BYE [RFC3261],
      UPDATE [RFC3311],             INFO [RFC6086],
      MESSAGE [RFC3428],            REFER [RFC3515],
      SUBSCRIBE [RFC3265],          NOTIFY [RFC3265],
      PUBLISH [RFC3903]

   The Geolocation header field MAY be included in any one of the
   above listed requests by a UA, and a 424 response to any one of the
   requests sent above.  Fully appreciating the caveats/warnings
   mentioned above, a SIP intermediary MAY add the Geolocation header
   field.

   A SIP intermediary MAY add a Geolocation header field if one is not
   present - for example, when a user agent does not support the
   Geolocation mechanism but their outbound proxy does and knows the
   Target's location, or any of a number of other use cases (see
   Section 3).

   The Geolocation header field MAY be present in a SIP request or
   response without the presence of a Geolocation-Routing header


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   (defined in Section 4.2). As stated in Section 4.2, the default
   value of Geolocation-Routing header-value is "no", meaning SIP
   intermediaries MUST NOT view (i.e., process, inspect or actively
   dereference) any direct or indirect location within this SIP
   message. This is for at least two fundamental reasons,

      1) to make the possibility of retention of the Target's location
         moot (because it was not viewed in the first place); and

      2) to prevent a different treatment of this SIP request based on
         the contents of the Location Information in the SIP request.

   Any locationValue MUST be related to the original Target. This is
   equally true for the location information in a SIP response, i.e.,
   from a SIP intermediary back to the Target as explained in Section
   3.4. SIP intermediaries SHOULD NOT modify or delete any existing
   locationValue(s). A use-case in which this would not apply would be
   where the SIP intermediary is an anonymizer. The problem with this
   scenario is that the geolocation included by the Target then becomes
   useless for the purpose or service they wanted to use (include) it
   for. For example, 911/emergency calling or finding the nearest
   (towing company/pizza delivery/dry cleaning) service(s) will not
   yield intended results if the Location Information were to be
   modified or deleted from the SIP request.


4.2 The Geolocation-Routing Header Field

   This document defines "Geolocation-Routing" as a new SIP header
   field registered by IANA, with the following ABNF [RFC5234]:

   message-header    /= Georouting-header ; (message-header from 3261)
   Georouting-header  = "Geolocation-Routing" HCOLON
                        ( "yes" / "no" / generic-value )
   generic-value      =  generic-param;  (from RFC 3261)

   HCOLON is defined in RFC3261 [RFC3261].

   The only defined values for the Geolocation-Routing header field are
   "yes" or "no". When the value is "yes", the locationValue can be
   used for routing decisions along the downstream signaling path by
   intermediaries. Values other than "yes" or "no" are permitted for
   future extensions. Implementations not aware of an extension MUST
   treat any other received value the same as "no".

   If no Geolocation-Routing header field is present in a SIP request,
   a SIP intermediary MAY insert this header. Without knowledge from a
   Rulemaker, the SIP intermediary inserting this header-value SHOULD
   NOT set the value to "yes", as this may be more permissive than the
   originating party intends. An easy way around this is to have the
   Target always insert this header-value as "no".



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   When this Geolocation-Routing header-value is set to "no", this
   means no locationValue (inserted by the originating UAC or any
   intermediary along the signaling path) can be used by any SIP
   intermediary to make routing decisions. Intermediaries that attempt
   to use the location information for routing purposes in spite of
   this counter indication could end up routing the request improperly
   as a result.  Section 4.4 describes the details on what a routing
   intermediary does if it determines it needs to use the location in
   the SIP request in order to process the message further. The
   practical implication is that when the Geolocation-Routing
   header-value is set to "no", if a cid:url is present in the SIP
   request, intermediaries MUST NOT view the location (because it is
   not for intermediaries to consider when processing the request), and
   if a location URI is present, intermediaries MUST NOT dereference
   it.  UAs are allowed to view location in the SIP request even when
   the Geolocation-Routing header-value is set to "no".  An LR MUST by
   default consider the Geolocation-Routing header-value as set to
   "no", with no exceptions, unless the header field value is set to
   "yes".

   A Geolocation-Routing header-value that is set to "no" has no
   special security properties. It is at most a request for behavior
   within SIP intermediaries. That said, if the Geolocation-Routing
   header-value is set to "no", SIP intermediaries are still to process
   the SIP request and send it further downstream within the signaling
   path if there are no errors present in this SIP request.

   The Geolocation-Routing header field satisfies the recommendations
   made in section 3.5 of RFC 5606 [RFC5606] regarding indication of
   permission to use location-based routing in SIP.

   SIP implementations are advised to pay special attention to the
   policy elements for location retransmission and retention described
   in RFC 4119.

   The Geolocation-Routing header field cannot appear without a
   header-value in a SIP request or response (i.e., a null value is not
   allowed). The absence of a Geolocation-Routing header-value in a SIP
   request is always the same as the following header field:

      Geolocation-Routing: no

   The Geolocation-Routing header field MAY be present without a
   Geolocation header field in the same SIP request. This concept is
   further explored in Section 4.2.1.


4.2.1 Explaining Geolocation-Routing header-value States

   The Geolocation header field contains a Target's location, and MUST
   NOT be present if there is no location information in this SIP
   request. The location information is contained in one or more


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   locationValues. These locationValues MAY be contained in a single
   Geolocation header field, or distributed among multiple Geolocation
   header fields. (See section 7.3.1 of RFC3261.)

   The Geolocation-Routing header field indicates whether or not SIP
   intermediaries can view and then route this SIP request based on the
   included (directly or indirectly) location information. The
   Geolocation-Routing header field MUST NOT appear more than once in
   any SIP request, and MUST NOT lack a header-value. The default or
   implied policy of a SIP request that does not have a
   Geolocation-Routing header field is the same as if one were present
   and the header-value were set to "no".

   There are only 3 possible states regarding the Geolocation-Routing
   header field

   - "no"
   - "yes"
   - no header-field present in this SIP request

   The expected results in each state are:

   If the Geolocation-Routing    Only possible interpretations:
   --------------------------    -----------------------------
   "no"                          SIP intermediaries MUST NOT process
                                 included geolocation information
                                 within this SIP request.

                                 SIP intermediaries inserting a
                                 locationValue into a Geolocation
                                 header field (whether adding to an
                                 existing header-value or inserting the
                                 Geolocation header field for the first
                                 time) MUST NOT modify or delete the
                                 received "no" header-value.


   "yes"                         SIP intermediaries can process
                                 included geolocation information
                                 within this SIP request, and can
                                 change the policy to "no" for
                                 intermediaries further downstream.


   Geolocation-Routing absent    If a Geolocation header field exists
                                 (meaning a locationValue is already
                                 present), a SIP intermediary MUST
                                 interpret the lack of a
                                 Geolocation-Routing header field as if
                                 there were one present and the
                                 header-value is set to "no".



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                                 If there is no Geolocation header
                                 field in this SIP request, the default
                                 Geolocation-Routing is open and can be
                                 set by a SIP intermediary or not at
                                 all.


4.3 424 (Bad Location Information) Response Code

   This SIP extension creates a new location-specific response code,
   defined as follows,

      424 (Bad Location Information)

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

   A SIP intermediary can also reject a location it receives from a
   Target when it understands the Target to be in a different location.
   The proper handling of this scenario, described in Section 3.4, is
   for the SIP intermediary to include the proper location in the 424
   Response.  This SHOULD be included in the response as a MIME message
   body (i.e., a location value), rather than as a URI; however, in
   cases where the intermediary is willing to share location with
   recipients but not with a user agent, a reference might be
   necessary.

   As mentioned in Section 3.4, it might be the case that the
   intermediary does not want to chance providing less accurate
   location information than the user agent; thus it will compose its
   understanding of where the user agent is in a separate <geopriv>
   element of the same PIDF-LO [RFC4119] message body in the SIP
   response (which also contains the Target's version of where it is).
   Therefore, both locations are included - each with different
   <method> elements.  The proper reaction of the user agent is to
   generate a new SIP request that includes this composed location
   object, and send it towards the original LR.  SIP intermediaries can
   verify that subsequent requests properly insert the suggested
   location information before forwarding said requests.

   SIP intermediaries that are forwarding (as opposed to generating) a
   424 response MUST NOT add, modify, or delete any location appearing
   in that response. This specifically applies to intermediaries that
   are between the 424 response generator and the original UAC.
   Geolocation and Geolocation-Error header fields and PIDF-LO body
   parts MUST remain unchanged, never added to or deleted.

   Section 4.4 describes a Geolocation-Error header field to provide
   more detail about what was wrong with the location information in
   the request.  This header field MUST be included in the 424 response.


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   It is only appropriate to generate a 424 response when the
   responding entity needs a locationValue and there are no values in
   the request that are usable by the responder, or when the responder
   has additional location information to provide. The latter case is
   shown in Figure 4 of section 3.4. There, a SIP intermediary is
   informing the upstream UA which location to include in the next SIP
   request.

   A 424 MUST NOT be sent in response to a request that lacks a
   Geolocation header entirely, as the user agent in that case may not
   support this extension at all.  If a SIP intermediary inserted a
   locationValue into a SIP request where one was not previously
   present, it MUST take any and all responsibility for the corrective
   action if it receives a 424 to a SIP request it sent.

   A 424 (Bad Location Information) response is a final response within
   a transaction, and MUST NOT terminate an existing dialog.


4.4 The Geolocation-Error Header Field

   As discussed in Section 4.3, more granular error notifications
   specific to location errors within a received request are required
   if the location inserting entity is to know what was wrong within
   the original request. The Geolocation-Error header field is used for
   this purpose.

   The Geolocation-Error header field is used to convey
   location-specific errors within a response.  The Geolocation-Error
   header field has the following ABNF [RFC5234]:


   message-header          /= Geolocation-Error
                              ; (message-header from 3261)
   Geolocation-Error        = "Geolocation-Error" HCOLON
                                locationErrorValue
   locationErrorValue       = location-error-code
                               *(SEMI location-error-params)
   location-error-code      = 1*3DIGIT
   location-error-params    = location-error-code-text
                              / generic-param ; from RFC3261
   location-error-code-text = "code" EQUAL quoted-string ; from RFC3261

   HCOLON, SEMI, and EQUAL are defined in RFC3261 [RFC3261]. DIGIT is
   defined in RFC5234 [RFC5234].


   The Geolocation-Error header field MUST contain only one
   locationErrorValue to indicate what was wrong with the locationValue
   the Location Recipient determined was bad. The locationErrorValue
   contains a 3-digit error code indicating what was wrong with the


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   location in the request.  This error code has a corresponding quoted
   error text string that is human understandable.  The text string is
   OPTIONAL, but RECOMMENDED for human readability, similar to the
   string phrase used for SIP response codes. That said, the strings
   are complete enough for rendering to the user, if so desired. The
   strings in this document are recommendations, and are not
   standardized - meaning an operator can change the strings - but MUST
   NOT change the meaning of the error code. Similar to how RFC 3261
   specifies, there MUST NOT be more than one string per error code.

   The Geolocation-Error header field MAY be included in any response
   to one of the SIP Methods mentioned in Section 4.1, so long as a
   locationValue was in the request part of the same transaction.  For
   example, Alice includes her location in an INVITE to Bob. Bob can
   accept this INVITE, thus creating a dialog, even though his UA
   determined the location contained in the INVITE was bad.  Bob merely
   includes a Geolocation-Error header value in the 200 OK to the
   INVITE informing Alice the INVITE was accepted but the location
   provided was bad.

   If, on the other hand, Bob cannot accept Alice's INVITE without a
   suitable location, a 424 (Bad Location Information) is sent. This
   message flow is shown in Figures 1, 2 or 3 in Sections 3.1, 3.2 and
   3.3 respectively.

   If Alice is deliberately leaving location information out of the LO
   because she does not want Bob to have this additional information,
   implementations should be aware that Bob could error repeatedly in
   order to receive more location information about Alice in a
   subsequent SIP request. Implementations MUST be on guard for this,
   by not allowing continually more information to be revealed unless
   it is clear that any LR is permitted by Alice to know all that Alice
   knows about her location. A limit on the number of such rejections
   to learn more location information SHOULD be configurable, with a
   RECOMMENDED maximum of 3 times for each related transaction.

   A SIP intermediary that requires Alice's location in order to
   properly process Alice's INVITE also sends a 424 with a
   Geolocation-Error code. This message flow is shown in Figure 4 of
   Section 3.4.

   If more than one locationValue is present in a SIP request and at
   least one locationValue is determined to be valid by the LR, the
   location in that SIP request MUST be considered good as far as
   location is concerned, and no Geolocation-Error is to be sent.

   Here is an initial list of location based error code ranges for any
   SIP response, including provisional responses (other than 100
   Trying) and the new 424 (Bad Location Information) response. These
   error codes are divided into 3 categories, based on how the response
   receiver should react to these errors.  There MUST be no more than
   one Geolocation-Error code in a SIP response, regardless of how many


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   locationValues there are in the correlating SIP request. There is no
   guidance given in this document as to which locationValue, when more
   than one was present in the SIP request, is related to the
   Geolocation-Error code; meaning that, somehow not defined here, the
   LR just picks one to error.

   o  1XX errors mean the LR cannot process the location within the
      request

      A non-exclusive list of reasons for returning a 1XX is

      - the location was not present or could not be found,
      - there was not enough location information to determine
        where the Target was,
      - the location information was corrupted or known to be
        inaccurate,

   o  2XX errors mean some specific permission is necessary to process
      the included location information.

   o  3XX errors mean there was trouble dereferencing the Location URI
      sent.

   Dereference attempts to the same request SHOULD be limited to 10
   attempts within a few minutes. This number SHOULD be configurable,
   but result in a Geolocation-Error: 300 error once reached.

   It should be noted that for non-INVITE transactions, the SIP
   response will likely be sent before the dereference response has
   been received. This document does not alter that SIP protocol
   reality. This means the receiver of any non-INVITE response to a
   request containing location SHOULD NOT consider a 200 OK to mean the
   act of dereferencing has concluded and the dereferencer  (i.e., the
   LR) has successfully received and parsed the PIDF-LO for errors and
   found none. The end of section 3.2 discusses how transaction timing
   considerations lead to this requirement.

   Additionally, if an LR cannot or chooses not to process location
   from a SIP request, a 500 (Server Internal Error) SHOULD be used
   with or without a configurable Retry-After header field. There is no
   special location error code for what already exists within SIP
   today.

   Within each of these ranges, there is a top level error as follows:

   Geolocation-Error: 100 ; code="Cannot Process Location"

   Geolocation-Error: 200 ; code="Permission To Use Location
                                  Information"

   Geolocation-Error: 300 ; code="Dereference Failure"



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   If an error recipient cannot process a specific error code (such as
   the 201 or 202 below), perhaps because it does not understand that
   specific error code, the error recipient SHOULD process the error
   code as if it originally were a top level error code where the X in
   X00 matches the specific error code. If the error recipient cannot
   process a non-100 error code, for whatever reason, then the error
   code 100 MUST be processed.

   There are two specific Geolocation-Error codes necessary to include
   in this document, both have to do with permissions necessary to
   process the SIP request; they are

   Geolocation-Error: 201 ; code="Permission To Retransmit Location
                                  Information to a Third Party"

   This location error is specific to having the Presence Information
   Data Format (PIDF-LO) [RFC4119] <retransmission-allowed> element set
   to "no". This location error is stating it requires permission
   (i.e., PIDF-LO <retransmission-allowed> element set to "yes") to
   process this SIP request further.  If the LS sending the location
   information does not want to give this permission, it will not
   change this permission in a new request. If the LS wants this
   message processed with the <retransmission-allowed> element set to
   "yes" it MUST choose another logical path (if one exists) for this
   SIP request.

   Geolocation-Error: 202 ; code="Permission to Route based on Location
                                  Information"

   This location error is specific to having the Geolocation-Routing
   header value set to "no". This location error is stating it requires
   permission (i.e., the Geolocation-Routing header value set to "yes")
   to process this SIP request further.  If the LS sending the location
   information does not want to give this permission, it will not
   change this permission in a new request. If the LS wants this
   message processed with the <retransmission-allowed> element set to
   "yes" it MUST choose another logical path (if one exists) for this
   SIP request.


4.5 Location URIs in Message Bodies

   In the case where an LR sends a 424 response and wishes to
   communicate suitable location by reference rather than by value, the
   424 MUST include a content-indirection body per RFC 4483.


4.6 Location Profile Negotiation

   The following is part of the discussion started in Section 3, Figure
   2, which introduced the concept of sending location indirectly.



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   If a location URI is included in a SIP request, the sending user
   agent MUST also include a Supported header field indicating which
   location profiles it supports. Two option tags for location profiles
   are defined by this document: "geolocation-sip" and
   "geolocation-http". Future specifications MAY define further
   location profiles per the IANA policy described in Section 8.3.

   The "geolocation-sip" option tag signals support for acquiring
   location information via the presence event package of SIP
   ([RFC3856]). A location recipient who supports this option can send
   a SUBSCRIBE request and parse a resulting NOTIFY containing a
   PIDF-LO object. The URI schemes supported by this option include
   "sip", "sips" and "pres".

   The "geolocation-http" option tag signals support for acquiring
   location information via an HTTP ([RFC2616]). A location recipient
   who supports this option can request location with an HTTP GET and
   parse a resulting 200 response containing a PIDF-LO object. The URI
   schemes supported by this option include "http" and "https". A
   failure to parse the 200 response, for whatever reason, will return
   a "Dereference Failure" indication to the original location sending
   user agent to inform it that location was not delivered as intended.

   If the location URI receiver does not understand the URI scheme sent
   to it, it will return an Unsupported header value of the option-tag
   from the SIP request, and include the option-tag of the preferred
   URI scheme in the response's Supported header field.

   See [ID-GEO-FILTERS] or [ID-HELD-DEREF] for more details on
   dereferencing location information.


5.  Geolocation Examples

5.1 Location-by-value (in Coordinate Format)

   This example shows an INVITE message with a coordinate location.  In
   this example, the SIP request uses a sips-URI [RFC3261], meaning
   this message is protected using TLS on a hop-by-hop basis.

   INVITE sips:bob@biloxi.example.com SIP/2.0
   Via: SIPS/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:target123@atlanta.example.com>
   Geolocation-Routing: no
   Accept: application/sdp, application/pidf+xml
   CSeq: 31862 INVITE
   Contact: <sips:alice@atlanta.example.com>
   Content-Type: multipart/mixed; boundary=boundary1


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   Content-Length: ...

   --boundary1

   Content-Type: application/sdp

   ...SDP goes here

   --boundary1

   Content-Type: application/pidf+xml
   Content-ID: <target123@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:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
          xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
          xmlns:gml="http://www.opengis.net/gml"
          xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
          entity="pres:alice@atlanta.example.com">
        <dm:device id="target123-1">
          <gp:geopriv>
            <gp:location-info>
              <gml:location>
                <gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
                  <gml:pos>32.86726 -97.16054</gml:pos>
                </gml:Point>
             </gml:location>
            </gp:location-info>
            <gp:usage-rules>
              <gbp:retransmission-allowed>false
              </gbp:retransmission-allowed>
              <gbp:retention-expiry>2010-11-14T20:00:00Z
              </gbp:retention-expiry>
            </gp:usage-rules>
            <gp:method>802.11</gp:method>
          </gp:geopriv>
          <dm:deviceID>mac:1234567890ab</dm:deviceID>
          <dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
        </dm:device>
      </presence>
   --boundary1--

   The Geolocation header field from the above INVITE:

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

   ... indicates the content-ID location [RFC2392] within the multipart
   message body of where location information is. The other message
   body part is SDP.  The "cid:" eases message body parsing and
   disambiguates multiple parts of the same type.


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   If the Geolocation header field did not contain a "cid:" scheme, for
   example, it could look like this location URI:

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

   ... the existence of a non-"cid:" scheme indicates this is a
   location URI, to be dereferenced to learn the Target's location. Any
   node wanting to know where the target is located would subscribe to
   the SIP presence event package [RFC3856] at

      sips:target123@server5.atlanta.example.com

   (see Figure 2 in Section 3.2 for this message flow).


5.2 Two Locations Composed in Same Location Object Example

   This example shows the INVITE message after a SIP intermediary
   rejected the original INVITE (say, the one in section 5.1). This
   INVITE contains the composed LO sent by the SIP intermediary which
   includes where the intermediary understands Alice to be. The rules
   of RFC 5491 [RFC5491] are followed in this construction.

   This example is here, but ought not be taken as occurring very
   often. In fact, this example is believed to be a corner case of
   location conveyance applicability.

   INVITE sips:bob@biloxi.example.com SIP/2.0
   Via: SIPS/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf0
   Max-Forwards: 70
   To: Bob <sips:bob@biloxi.example.com>
   From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
   Call-ID: 3848276298220188512@atlanta.example.com
   Geolocation: <cid:target123@atlanta.example.com>
   Geolocation-Routing: no
   Accept: application/sdp, application/pidf+xml
   CSeq: 31863 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: <target123@atlanta.example.com>


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   <?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:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
          xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
          xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
          xmlns:gml="http://www.opengis.net/gml"
          entity="pres:alice@atlanta.example.com">
        <dm:device id="target123-1">
          <gp:geopriv>
            <gp:location-info>
              <gml:location>
                <gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
                  <gml:pos>32.86726 -97.16054</gml:pos>
                </gml:Point>
              </gml:location>
            </gp:location-info>
            <gp:usage-rules>
              <gbp:retransmission-allowed>false
              </gbp:retransmission-allowed>
             <gbp:retention-expiry>2010-11-14T20:00:00Z
              </gbp:retention-expiry>
            </gp:usage-rules>
            <gp:method>802.11</gp:method>
          </gp:geopriv>
          <dm:deviceID>mac:1234567890ab</dm:deviceID>
          <dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
        </dm:device>
        <dm:person id="target123">
          <gp:geopriv>
            <gp:location-info>
              <cl:civicAddress>
                <cl:country>US</cl:country>
                <cl:A1>Texas</cl:A1>
                <cl:A3>Colleyville</cl:A3>
                <cl:RD>Treemont</cl:RD>
                <cl:STS>Circle</cl:STS>
                <cl:HNO>3913</cl:HNO>
                <cl:FLR>1</cl:FLR>
                <cl:NAM>Haley's Place</cl:NAM>
                <cl:PC>76034</cl:PC>
              </cl:civicAddress>
            </gp:location-info>
            <gp:usage-rules>
              <gbp:retransmission-allowed>false
              </gbp:retransmission-allowed>
              <gbp:retention-expiry>2010-11-14T20:00:00Z
              </gbp:retention-expiry>
            </gp:usage-rules>
            <gp:method>triangulation</gp:method>
          </gp:geopriv>


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          <dm:timestamp>2010-11-04T12:28:04Z</dm:timestamp>
        </dm:person>
      </presence>
   --boundary1--


6.  Geopriv Privacy Considerations

   Location information is considered by most to be highly sensitive
   information, requiring protection from eavesdropping and altering in
   transit.  [RFC3693] originally articulated rules to be followed by
   any protocol wishing to be considered a "Using Protocol", specifying
   how a transport protocol meets those rules.  [RFC6280] updates
   the guidance in RFC3693 to include subsequently introduced
   entities and concepts in the geolocation architecture.

   RFC5606 explores the difficulties inherent in mapping the GEOPRIV
   architecture onto SIP elements. In particular, the difficulties of
   defining and identifying recipients of location information are
   given in that document, along with guidance in Section 3.3.2 on the
   use of location by-reference mechanisms to preserve confidentiality
   of location information from unauthorized recipients.

   In a SIP deployment, location information may be added by any of
   several elements, including the originating user agent or a proxy
   server. In all cases, the Rule Maker associated with that location
   information decides which entity adds location information and what
   access control rules apply. For example, a SIP user agent that does
   not support the Geolocation header may rely on a proxy server under
   the direction of the Rule Maker adding a Geolocation header with a
   reference to location information. The manner in which the Rule
   Maker operates on these devices is outside the scope of this
   document.

   The manner in which SIP implementations honor the Rule Maker's
   stipulations for access control rules (including retention and
   retransmission) is application-specific and not within the scope of
   SIP protocol operations. Entities in SIP networks that fulfill the
   architectural roles of the Location Server or Location Recipient
   treat the privacy rules associated with location information per
   the guidance in [RFC6280] section 4.2.1. In particular, RFC4119
   (especially 2.2.2) gives guidance for handling access control rules;
   SIP implementations should furthermore consult the emendations in
   RFC5606.


7.  Security Considerations

   Conveyance of physical location of a UA raises privacy concerns,
   and depending on use, there probably will be authentication and
   integrity concerns.  This document calls for conveyance to
   be accomplished through secure mechanisms, like S/MIME encrypting


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   message bodies (although this is not widely deployed), TLS
   protecting the overall signaling or conveyance location by-reference
   and requiring all entities that dereference location to authenticate
   themselves.  In location-based routing cases, encrypting the
   location payload 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. Data can only be encrypted to a
   particular, anticipated target, and thus if multiple recipients need
   to inspect a piece of data, and those recipients cannot be predicted
   by the sender of data, encryption is not a very feasible choice.
   Securing the location hop-by-hop, using TLS, protects the message
   from eavesdropping and modification in transit, but exposes the
   information to all proxies on the path as well as the endpoint.  In
   most cases, the UA has no trust relationship with the proxy or
   proxies providing location-based routing services, so such
   end-to-middle solutions might not be appropriate either.

   When location information is conveyed by reference, however, one can
   properly authenticate and authorize each entity that wishes to
   inspect location information. This does not require that the sender
   of data anticipate who will receive data, and it does permit
   multiple entities to receive it securely, but it does not however
   obviate the need for pre-association between the sender of data and
   any prospective recipients. Obviously, in some contexts this
   pre-association cannot be presumed; when it is not, effectively
   unauthenticated access to location information must be permitted. In
   this case, choosing pseudo-random URIs for location by-reference,
   coupled with path encryption like SIPS, can help to ensure that only
   entities on the SIP signaling path learn the URI, and thus restores
   rough parity with sending location by-value.

   Location information is especially sensitive when the identity of
   its Target is obvious. Note that there is the ability, according to
   [RFC3693] to have an anonymous identity for the Target's location.
   This is accomplished by use of an unlinkable pseudonym in the
   "entity=" attribute of the <presence> element  [RFC4479]. Though,
   this can be problematic for routing messages based on location
   (covered in the document above). Moreover, anyone fishing for
   information would correlate the identity at the SIP layer with that
   of the location information referenced by SIP signaling.

   When a UA inserts location, the UA sets the policy on whether to
   reveal its location along the signaling path - as discussed in
   Section 4, as well as flags in the PIDF-LO [RFC4119].  UAC
   implementations MUST make such capabilities conditional on explicit
   user permission, and MUST alert the user that location is being
   conveyed.

   This SIP extension offers the default ability to require permission
   to process location while the SIP request is in transit.  The
   default for this is set to "no". There is an error explicitly


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   describing how an intermediary asks for permission to view the
   Target's location, plus a rule stating the user has to be made aware
   of this permission request.

   There is no end-to-end integrity on any locationValue or
   locationErrorValue header field parameter (or middle-to-end if the
   value was inserted by a intermediary), so recipients of either
   header field need to implicitly trust the header field contents, and
   take whatever precautions each entity deems appropriate given this
   situation.

8.  IANA Considerations

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

   [Editor's Note: RFC-Editor - within the IANA section, please
                   replace "this doc" with the assigned RFC number,
                   if this document reaches publication.]


8.1 IANA Registration for the SIP Geolocation Header Field

   The SIP Geolocation Header Field is created by this document, with
   its definition and rules in Section 4.1 of this document, and should
   be added to the IANA sip-parameters registry with the following
   actions

   1. Update the Header Fields registry with

   Registry:
     Header Name        compact    Reference
     -----------------  -------    ---------
     Geolocation                   [this doc]


8.2 IANA Registration for the SIP Geolocation-Routing Header Field

   The SIP Geolocation-Routing Header Field is created by this document,
   with its definition and rules in Section 4.2 of this document, and
   should be added to the IANA sip-parameters registry with the
   following action

   1. Update the Header Fields registry with

   Registry:
     Header Name          compact    Reference
     -----------------    -------    ---------
     Geolocation-Routing             [this doc]




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8.3 IANA Registration for Location Profiles

   This document defines two new SIP option tags: "geolocation-sip" and
   "geolocation-http" to be added to the IANA sip-parameters Options
   Tags registry.

Name             Description                                 Reference
-----------      ------------------------------------------  ---------
geolocation-sip  The "geolocation-sip" option tag signals    [this doc]
                 support for acquiring location information
                 via the presence event package of SIP
                 (RFC 3856). A location recipient who
                 supports this option can send a SUBSCRIBE
                 request and parse a resulting NOTIFY
                 containing a PIDF-LO object. The URI
                 schemes supported by this option include
                 "sip", "sips" and "pres".

geolocation-http The "geolocation-http" option tag signals   [this doc]
                 support for acquiring location information
                 via an HTTP ([RFC2616]). A location
                 recipient who supports this option can
                 request location with an HTTP GET and
                 parse a resulting 200 response containing
                 a PIDF-LO object. The URI schemes
                 supported by this option include "http"
                 and "https".

   The names of profiles are SIP option-tags, and the guidance in this
   document does not supersede the option-tag assignment guidance in
   [RFC3261] (which requires a Standards Action for the assignment of a
   new option tag). This document does however stipulate that
   option-tags included to convey the name of a location profile per
   this definition MUST begin with the string "geolocation" followed by
   a dash. All such option tags should describe protocols used to
   acquire location by reference: these tags have no relevance to
   location carried in SIP requests by value, which use standard MIME
   typing and negotiation.


8.4 IANA Registration for 424 Response Code

   In the SIP Response Codes registry, the following is added

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

   Registry:
     Response Code                               Reference
     ------------------------------------------  ---------
     Request Failure 4xx


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       424 Bad Location Information              [this doc]


   This SIP Response code is defined in section 4.3 of this document.


8.5 IANA Registration of New Geolocation-Error Header Field

   The SIP Geolocation-error header field is created by this document,
   with its definition and rules in Section 4.4 of this document, to be
   added to the IANA sip-parameters registry with two actions

   1. Update the Header Fields registry with

   Registry:
     Header Name        compact    Reference
     -----------------  -------    ---------
     Geolocation-Error             [this doc]

   2. In the portion titled "Header Field Parameters and Parameter
      Values", add

                                            Predefined
   Header Field        Parameter Name       Values      Reference
   -----------------   -------------------  ----------  ---------
   Geolocation-Error   code                 yes         [this doc]


8.6 IANA Registration for the SIP Geolocation-Error Codes

   This document creates a new registry for SIP, called
   "Geolocation-Error Codes." Geolocation-Error codes provide reason
   for the error discovered by Location Recipients, categorized by
   action to be taken by error recipient.  The initial values for this
   registry are shown below.

  Registry Name: Geolocation-Error Codes
  Reference: [this doc]
  Registration Procedures: Specification Required

  Code Default Reason Phrase                                Reference
  ---- ---------------------------------------------------  ---------
  100  "Cannot Process Location"                            [this doc]

  200  "Permission To Use Location Information"             [this doc]

  201  "Permission To Retransmit Location Information to a Third Party"
                                                            [this doc]

  202  "Permission to Route based on Location Information"  [this doc]

  300  "Dereference Failure"                                [this doc]


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   Details of these error codes are in Section 4.4 of this
   document.


9.  Acknowledgements

   To Dave Oran for helping to shape this idea.

   To Dean Willis for 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, Ted Hardie, Shida Shubert, Umesh Sharma, Richard
   Barnes, Dan Wing, Matt Lepinski, John Elwell, Thomas Stach,
   Jacqueline Lee and Adam Roach for constructive feedback and nits
   checking.

   Special thanks to Paul Kyzivat for his help with the ABNF in this
   document and to Robert Sparks for many helpful comments and the
   proper construction of the Geolocation-Error header field.

   And finally, to Spencer Dawkins for giving this doc a good scrubbing
   to make it more readable.


10. References

10.1 Normative References

 [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 2392, August 1998

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

 [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


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           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.

 [RFC6086] C. Holmberg, E. Burger, H. Kaplan, "Session Initiation
           Protocol (SIP) INFO Method and Package Framework", RFC 6086,
           January 2011

 [RFC3515] R. Sparks, "The Session Initiation Protocol (SIP) Refer
           Method", RFC 3515, April 2003

 [RFC3903] Niemi, A, "Session Initiation Protocol (SIP) Extension
           for Event State Publication", RFC 3903, October 2004.

 [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for Syntax
           Specifications: ABNF", STD 68, RFC 5234, January 2008.

 [RFC4479] J. Rosenberg, "A Data Model for Presence", RFC 4479, July
           2006

 [RFC4483] E. Berger, "A Mechanism for Content Indirection in SIP", RFC
           4483, May 2006

 [RFC5491] J. Winterbottom, M. Thomson, H. Tschofenig, "GEOPRIV PIDF-LO
           Usage Clarification, Considerations, and Recommendations ",
           RFC 5491, March 2009

 [RFC5870] A. Mayrhofer, C. Spanring, "A Uniform Resource Identifier
           for Geographic Locations ('geo' URI)", RFC 5870, June 2010

 [RFC2616] R. Fielding, J. Gettys, J., Mogul, H. Frystyk, L.,
           Masinter, P. Leach, T. Berners-Lee, "Hypertext Transfer
           Protocol - HTTP/1.1", RFC 2616, June 1999


10.2 Informative References

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

 [RFC2818] E. Rescorla, "HTTP Over TLS", RFC 2818, May 2000

 [RFC5606] J. Peterson, T. Hardie, J. Morris, "Implications of
           'retransmission-allowed' for SIP Location Conveyance",
           RFC5606, Oct 2008

 [ID-GEO-FILTERS] R. Mahy, B. Rosen, H. Tschofenig, "Filtering Location
           Notifications in SIP", draft-ietf-geopriv-loc-filters, "work


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           in progress", March 2010

 [ID-HELD-DEREF] J. Winterbottom, H. Tschofenig, H. Schulzrinne, M.
           Thomson, M. Dawson, "A Location Dereferencing Protocol Using
           HELD", "work in progress", June 2011

 [RFC6280] R. Barnes, M. Lepinski, A. Cooper, J, Morris, H.
           Tschofenig, H. Schulzrinne, "An Architecture for Location
           and Location Privacy in Internet Applications",
           draft-ietf-geopriv-arch, "work in progress", October 2010


Authors' Addresses

   James Polk
   Cisco Systems
   3913 Treemont Circle
   Colleyville, Texas  76034

   33.00111N
   96.68142W

   Phone: +1-817-271-3552

   Email: jmpolk@cisco.com


   Brian Rosen
   NeuStar, Inc.
   470 Conrad Dr.
   Mars, PA  16046

   40.70497N
   80.01252W

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

   Jon Peterson
   NeuStar, Inc.

   Email: jon.peterson@neustar.biz


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. This
   is from the original requirements draft that has since evolved into
   the solution document (that is above). This has been kept for
   historical reasons.



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   If a requirement is not obvious in intent, a motivational statement
   is included below it.

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: to guarantee 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: if a UAC has moved prior to the establishment of a
          dialog between UAs, the UAC must be able to send location
          information.  If location has been conveyed, and the UA
          moves, the UAC must be able to update the location previously
          conveyed to other parties.

   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 [RFC4119] is a mandatory to implement format for
          location conveyance within SIP.

   Motivation:  interoperability with other IETF location protocols and
          Mechanisms.

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



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   Motivation: Failure to receive location when it is expected can
          happen because the UAC does not implement this extension, or
          because the UAC implements the extension, but does not know
          where the Target is.  This may be, for example, due to the
          failure of the access network to provide a location
          acquisition mechanism the UAC supports.  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.

          The SIPCORE WG reached consensus that this be allowed, but
          not to communicate the UAS's location; rather for a SIP
          intermediary to inform the UAC which location to include in
          its next SIP request (as a matter of correcting what was
          originally sent by the UAC).

   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 also 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 network assertion of location
            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 can have
         widely varying access network arrangements, including VPN
         tunnels and roaming mechanisms, it can be difficult for a
         network to reliably know the location of the endpoint.
         Proxies SHOULD NOT assert location of an endpoint unless the
         SIP signaling network has reliable knowledge of the actual
         location of the Targets.



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




















































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