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RFC 6442

Location Conveyance for the Session Initiation Protocol

Pages: 35
Proposed Standard
Errata
Updated by:  82628787

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Internet Engineering Task Force (IETF)                           J. Polk
Request for Comments: 6442                                 Cisco Systems
Category: Standards Track                                       B. Rosen
ISSN: 2070-1721                                              J. Peterson
                                                                 NeuStar
                                                           December 2011

        Location Conveyance for the Session Initiation Protocol

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 is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6442. 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 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 Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   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. Introduction ....................................................3 2. Conventions and Terminology Used in This Document ...............4 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 ................6 3.4. SIP Intermediary Replacing Bad Location ....................7 4. SIP Extensions for Geolocation Conveyance .......................8 4.1. The Geolocation Header Field ...............................8 4.2. The Geolocation-Routing Header Field ......................11 4.2.1. Explaining Geolocation-Routing Header-Value States .............................................12 4.3. 424 (Bad Location Information) Response Code ..............14 4.4. The Geolocation-Error Header Field ........................15 4.5. Location URIs in Message Bodies ...........................19 4.6. Location Profile Negotiation ..............................19 5. Geolocation Examples ...........................................20 5.1. Location-by-Value (in Coordinate Format) ..................20 5.2. Two Locations Composed in Same Location Object Example ....21 6. Geopriv Privacy Considerations .................................23 7. Security Considerations ........................................24 8. IANA Considerations ............................................26 8.1. IANA Registration for the SIP Geolocation Header Field ....26 8.2. IANA Registration for the SIP Geolocation-Routing Header Field ..............................................26 8.3. IANA Registration for Location Profiles ...................27 8.4. IANA Registration for 424 Response Code ...................27 8.5. IANA Registration of New Geolocation-Error Header Field ...28 8.6. IANA Registration for the SIP Geolocation-Error Codes .....28 9. Acknowledgements ...............................................29 10. References ....................................................29 10.1. Normative References .....................................29 10.2. Informative References ...................................31 Appendix A. Requirements for SIP Location Conveyance ..............32
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1. 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 that 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 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.
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2. 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]. Furthermore, this document uses numerous terms defined in [RFC3693], including: Location Object, Location Recipient, Location Server, Target, Rule Maker, and Using Protocol.

3. Overview of SIP Location Conveyance

An operational overview of SIP location conveyance can be shown in four 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
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   location to Bob (e.g., Bob "cannot parse the location provided", or
   "there is not enough location information to determine where Alice
   is").

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 third party server. Alice SIP Intermediary Bob LS | | | | | Request w/Location URI | | |----------------------------------->| | | | Dereference | | | Request | | (To: Location URI) | | |---------------->| | | | | | Dereference | | | Response | | (includes Location Object) | | |<----------------| | 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; 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
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   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

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 an 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 that selects forwarding destinations based on the geographical location information contained in the SIP request. 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 that 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
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   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 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
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   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 of 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
   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, in that scenario, the SIP intermediary
   would 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 RFC 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)
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   geoloc-param       = generic-param ; (from RFC 3261)

   HCOLON, COMMA, LAQUOT, RAQUOT, and SEMI are defined in [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
   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
   criteria in [RFC3693] 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.
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   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
   (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 for which they wanted to use
   (include) it.  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.
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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 RFC 3261) Georouting-header = "Geolocation-Routing" HCOLON ( "yes" / "no" / generic-value ) generic-value = generic-param; (from RFC 3261) HCOLON is defined in [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 Rule Maker, 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". When this Geolocation-Routing header-value is set to "no", this means no locationValue (inserted by the originating User Agent Client (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 gives 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); 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".
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   A Geolocation-Routing header-value that is set to "no" has no special
   security properties.  At most, it is 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 it MUST NOT be present if there is no location information in this SIP request. The location information is contained in one or more 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 RFC 3261.) 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".
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   There are only three 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 as follows:

   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".

                                 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.
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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 Presence Information Data Format Location Object (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 response 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 response 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 RFC 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 RFC 3261 location-error-code-text = "code" EQUAL quoted-string ; from RFC 3261 HCOLON, SEMI, and EQUAL are defined in [RFC3261]. DIGIT is defined in [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 response 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) response 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 repeatedly error 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 three 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 response 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.
Top   ToC   RFC6442 - Page 17
   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 three 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
   locationValues there are in the correlating SIP request.  When more
   than one locationValue is present in a SIP request, this mechanism
   provides no indication to which one the Geolocation-Error code
   corresponds.  If multiple errors are present, the LR applies local
   policy to select one.

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

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

      - the location was not present or could not be found in the SIP
        request,

      - 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 response 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.
Top   ToC   RFC6442 - Page 18
   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"

   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 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
Top   ToC   RFC6442 - Page 19
   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 location-by- value, the 424 response 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. 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 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 [GEO-FILTERS] or [HELD-DEREF] for more details on dereferencing location information.
Top   ToC   RFC6442 - Page 20

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 Transport Layer Security (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 Content-Length: ... --boundary1 Content-Type: application/sdp ...Session Description Protocol (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>
Top   ToC   RFC6442 - Page 21
                </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.

   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 that includes where the intermediary understands Alice to be. The rules of RFC 5491 [RFC5491] are followed in this construction.
Top   ToC   RFC6442 - Page 22
   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>
   <?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
Top   ToC   RFC6442 - Page 23
              </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>
          <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 RFC 3693 to include subsequently introduced entities and concepts in the geolocation architecture.
Top   ToC   RFC6442 - Page 24
   RFC 5606 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, RFC 4119
   (especially Section 2.2.2) gives guidance for handling access control
   rules; SIP implementations should furthermore consult the
   recommendations in RFC 5606.

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 Secure/Multipurpose Internet Mail Extensions (S/MIME) encrypting 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 User Agent Server (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
Top   ToC   RFC6442 - Page 25
   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; however, it does not 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 pseudorandom URIs for location-by-reference,
   coupled with path encryption like Session Initiation Protocol Secure
   (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 the 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 [RFC4479]).  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 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.
Top   ToC   RFC6442 - Page 26
   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).

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 it has been added to the IANA sip-parameters registry as follows: The Header Fields registry has been updated with: Header Name Compact Reference ----------------- ------- --------- Geolocation [RFC6442]

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 it has been added to the IANA sip-parameters registry as follows. The Header Fields registry has been updated with: Header Name Compact Reference ----------------- ------- --------- Geolocation-Routing [RFC6442]
Top   ToC   RFC6442 - Page 27

8.3. IANA Registration for Location Profiles

This document defines two new SIP option tags: "geolocation-sip" and "geolocation-http" that have been added to the IANA sip-parameters Options Tags registry as follows. Name Description Reference ----------- ------------------------------------------ --------- geolocation-sip The "geolocation-sip" option tag signals [RFC6442] 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 [RFC6442] support for acquiring location information via HTTP (RFC 2616). 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). However, this document does 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 6442 Response code: 424 (recommended number to assign) Default reason phrase: Bad Location Information
Top   ToC   RFC6442 - Page 28
   Registry:
     Response Code                               Reference
     ------------------------------------------  ---------
     Request Failure 4xx
       424 Bad Location Information              [RFC6442]

   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 [RFC6442] 2. In the portion titled "Header Field Parameters and Parameter Values", add: Predefined Header Field Parameter Name Values Reference ----------------- ------------------- ---------- --------- Geolocation-Error code yes [RFC6442]

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: [RFC6442] Registration Procedures: Specification Required Code Default Reason Phrase Reference ---- --------------------------------------------------- --------- 100 "Cannot Process Location" [RFC6442] 200 "Permission To Use Location Information" [RFC6442] 201 "Permission To Retransmit Location Information to a Third Party" [RFC6442]
Top   ToC   RFC6442 - Page 29
   202  "Permission to Route based on Location Information"  [RFC6442]

   300  "Dereference Failure"                                [RFC6442]

   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 nit 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 document a good scrubbing to make it more readable.

10. References

10.1. Normative References

[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource Locators", RFC 2392, August 1998. [RFC3856] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", RFC 3856, August 2004.
Top   ToC   RFC6442 - Page 30
   [RFC3859]  Peterson, J., "Common Profile for Presence (CPP)", RFC
              3859, August 2004.

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

   [RFC3311]  Rosenberg, J., "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]  Holmberg, C., Burger, E., and H. Kaplan, "Session
              Initiation Protocol (SIP) INFO Method and Package
              Framework", RFC 6086, January 2011.

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

   [RFC3903]  Niemi, A., Ed., "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]  Rosenberg, J., "A Data Model for Presence", RFC 4479, July
              2006.

   [RFC4483]  Burger, E., Ed., "A Mechanism for Content Indirection in
              Session Initiation Protocol (SIP) Messages", RFC 4483, May
              2006.

   [RFC5491]  Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
              Presence Information Data Format Location Object (PIDF-LO)
              Usage Clarification, Considerations, and Recommendations",
              RFC 5491, March 2009.

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

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

[RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC5606] Peterson, J., Hardie, T., and J. Morris, "Implications of 'retransmission-allowed' for SIP Location Conveyance", RFC 5606, August 2009. [GEO-FILTERS] Mahy, R., Rosen, B., and H. Tschofenig, "Filtering Location Notifications in SIP", Work in Progress, March 2010. [HELD-DEREF] Winterbottom, J., Tschofenig, H., Schulzrinne, H., Thomson, M., and M. Dawson, "A Location Dereferencing Protocol Using HELD", Work in Progress, October 2011. [RFC6280] Barnes, R., Lepinski, M., Cooper, A., Morris, J., Tschofenig, H., and H. Schulzrinne, "An Architecture for Location and Location Privacy in Internet Applications", BCP 160, RFC 6280, July 2011.
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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 text is from a draft version of the location conveyance requirements that has since evolved into this document (RFC 6442). It has been kept for historical reasons. 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.
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          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.

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