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Versions: 00 01                                                         
Internet Engineering Task Force                           James M. Polk
Internet Draft                                            Cisco Systems
Expiration: April 27th, 2003                                Brian Rosen
File: draft-polk-sipping-location-requirements-01.txt           Marconi





           Session Initiation Protocol Location Conveyance

                           October 27th, 2003




Status of this Memo

   This document is an Internet-Draft and is in full conformance
   with all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts.

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Abstract

   This document presents the framework and requirements for an
   extension to the Session Initiation Protocol (SIP) [1] for
   conveyance of user location information from a Session Initiation
   Protocol (SIP) user agent to another SIP entity.  We consider cases
   where location information is conveyed from end to end, as well as
   cases where message routing by intermediaries is influenced by the
   location of the session initiator.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  2
       1.1 Conventions . . . . . . . . . . . . . . . . . . . . . . .  3
       1.2 Changes from -00  . . . . . . . . . . . . . . . . . . . .  3
   2.  In the Body or in a Header  . . . . . . . . . . . . . . . . .  3
   3.  Scope of Location in a Message Body . . . . . . . . . . . . .  4
   4.  Requirements for UA-to-UA Location Conveyance . . . . . . . .  4
   5.  Requirements for UA-to-Proxy Server Location Conveyance . . .  5
   6.  Additional Requirements for Emergency Calls . . . . . . . . .  5
   7.  Current Known Open issues . . . . . . . . . . . . . . . . . .  6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  6
   9.  IANA Considerations   . . . . . . . . . . . . . . . . . . . .  7
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   12. Author Information  . . . . . . . . . . . . . . . . . . . . .  8


1.  Introduction

   This document presents the framework and requirements for an
   extension to the Session Initiation Protocol (SIP) [1] for
   conveyance of user location information object described by [7] from
   a SIP User Agent to another SIP entity.

   There are several situations in which it is appropriate for SIP to
   be used to convey Location Information (LI) from one SIP entity to
   another.  This document specifies requirements when a SIP UAC knows
   its location by some means not specified herein, and needs to inform
   another SIP entity.  One example is to reach your nearest pizza
   parlor.  A chain of pizza parlors may have a single well known uri
   (sip:pizzaparlor.com), that is forwarded to the closest franchise by
   the pizzaparlor.com proxy server.  The receiving franchise UAS uses
   the location information of the UAC to schedule your delivery.

   Another important example is emergency calling.  A call to
   sip:sos@example.com is an emergency call as in [3].  The example.com
   proxy server must route the call to the correct emergency response
   center (ERC) determined by the location of the caller. At the ERC,
   the UAS must determine the correct police/fire/ambulance/...
   service, which is also based on your location.  In many
   jurisdictions, accurate location information is a required component
   of a call to an emergency center.

   A third example is a direction service, which might give you verbal
   directions to a venue from your present position.  This is a case
   where only the destination UAS needs to receive the location
   information.

   This document does not discuss how the UAC discovers or is


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   configured with its location (either coordinate based or civil
   based).  It also does not discuss the contents of the Location
   Object (LO).  It does specify the requirements for the "using
   protocol" in [7].


1.1  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described
   in [2].


1.2  Changes from -00 Version

   This is a list of the changes that have been made from the -00
   version of this ID:

   - Brian Rosen was brought on as a co-author

   - Requirements that a location header were negatively received in
     the previous version of this document.  AD and chair advice was to
     move all location information into a message body (and stay away
     from headers)

   - Added a section of "emergency call" specific requirements

   - Added an Open Issues section to mention what hasn't been resolved
     yet in this effort


2.  In the Body or in a Header

   When one user agent wants to inform another user agent where they
   are, it seems reasonable to have this accomplished by placing the
   location information (coordinate or civil) in an S/Mime registered
   and encoded message body, and sending it as part of a SIP request or
   response.  No routing of the request based on the location
   information is required in this case; therefore no SIP Proxies
   between these two UAs need to view the location information
   contained in the SIP messages.

   Although SIP [1} does not permit a proxy server to modify or delete
   a body, there is no restriction on viewing bodies.  However, S/MIME
   protection implemented on bodies is only specified between UAS and
   UAC and if engaged, would render the location object opaque to a
   proxy server.  This problem is similar to that raised in Session
   Policy [8], where an intermediary may need information in a body,
   such as IP address of media streams or codec choices to route a call
   properly.  Requirements in [8] are applicable to routing based on


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   location, and are incorporated in these requirements by reference.

   It is conceivable to create a new header for location information.
   However, [7] prefers S/MIME for security of Location Information,
   and indeed S/MIME is preferable in SIP for protecting one part of a
   message.  Accordingly, these requirements specify location be
   carried in a body.

   It is the use of S/MIME however, that limits routing based on
   location.  Therefore, it seems appropriate to require that, where
   routing is dependent on location, protection of the location
   information object be accomplished by other mechanisms, probably TLS
   ("sips:" from [1]).  It is envisioned that S/MIME SHOULD be used
   when location information is not required by proxy servers, and TLS
   SHOULD be used when it is.

   This document does not address the behavior or configuration of SIP
   Proxy Servers in these cases in order to accomplish location-
   sensitive routing.  That is out of scope, and left for further
   (complementary) efforts.


3.  Scope of Location in a Message Body

   If the location information is to be contained within a message
   body, and either another body (SDP for example) is also to be sent
   in the message, or the LO is to be protected with S/MIME, the rules
   stated in section 7 of [1] regarding multipart MIME bodies MUST be
   followed.  The format and privacy/security rules of the location
   information SHOULD be defined within the Geopriv WG.


4.  Requirements for UA-to-UA Location Conveyance

   The following are the requirements for UA-to-UA Location Conveyance
   situations:

    U-U1 - MUST work with dialog-initiating SIP Requests and responses,
           as well as the SIP MESSAGE method[4], and SHOULD work with
           most SIP messages.

    U-U2 - UAC Location information SHOULD remain confidential in route
           to the destination UA

    U-U3 - The privacy and security rules established within the
           Geopriv Working Group that would categorize SIP as a 'using
           protocol' MUST be met [7]






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5.  Requirements for UA-to-Proxy Server Location Conveyance

   The following are the requirements for UA-to-Proxy Server Location
   Conveyance situations:

    U-PS1 - MUST work with dialog-initiating SIP Requests and
            responses, as well as the SIP MESSAGE method[4], and SHOULD
            work with most SIP messages.

    U-PS2 - UAC location information SHOULD remain confidential in
            route to the destination, but MUST be useable by
            intermediary proxy servers.

    U-PS3 - The privacy and security rules established within the
            Geopriv Working Group which would categorize SIP as a
            'using protocol' MUST be met [7]

    U-PS4 - Modification or removal of the LO by proxy servers MUST NOT
            be required

    U-PS5 - any mechanism used to prevent unwanted observation of this
            Location Header(s) CANNOT fail the SIP Request if not
            understood by intermediary SIP entities or the destination
            UAS

    U-PS6 – It MUST be possible for a proxy server to assert the
            validity of the location information provided by the UA.
            Alternatively, it is acceptable for there to be a mechanism
            for a proxy server to assert a location object itself.


6. Additional Requirements for Emergency Calls

   Emergency calls have requirements that are not generally important
   to other uses for location in SIP:

   Emergency calls presently have between 2 and 8-second call setup
   times.  There is ample evidence that the longer call setup end of
   the range causes an unacceptable number of callers to abandon the
   call before it is completed.  Two-second call completion time is a
   goal of many existing emergency call centers.  Allocating 25% of the
   call set up for processing privacy concerns seems reasonable; 1
   second would be 50% of the goal, which seems unacceptable; less than
   0.5 second seems unachievable, therefore:

    E-1 - Privacy mechanisms MUST add no more than 0.5 second of call
          setup time when implemented in present technology UAs and
          Proxy Servers.

   It may be acceptable for full privacy mechanisms related to the
   location of the UAC (and it's user) to be tried on an initial


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   attempt to place a call, as long as the call attempt may be retried
   without the mechanism if the first attempt fails.  Abandoning
   privacy in cases of failure of the privacy mechanism might be
   subject to user preference, although such a feature would be within
   the domain of a UA implementation and thus not subject to
   standardization.  It should be noted that some jurisdictions have
   laws that explicitly deny any expectation of location privacy when
   making an emergency call.

    E-2 – Privacy mechanisms MUST NOT be mandatory for successful
          conveyance of location during an (sos-type) emergency call.

    E-3 – The retention and retransmission policy of the ERC must be
          able to be made available to the user, and override the
          user's normal policy when local regulation governs such
          retention and retransmission.  As in E-2 above, requiring the
          use of the ERC's retention and/or retransmission policy may
          be subject to user preference although in most jurisdictions,
          local laws specify such policies and may not be overridden by
          user preference.


7.  Current Known Open issues

   This is a list of open issues that have not yet been addressed to
   conclusion:

   - Whether self signed S/MIME bodies can work in both directions in
     the emergency call scenario (to and from an ERC) as in [9].  It
     appears that document covers self-signed certs from the UA to ERC
     direction, but it is not clear it solves communications in the
     reverse direction.

   - If S/MIME is chosen as a SHOULD (in general, vs. TLS), this doc
     might consider stipulating a special purpose Proxy (an "emergency
     services" proxy) that can process location information (a Geopriv
     LO) and route the message directly to the appropriate ERC.

       At Issue: plain "vanilla" proxies probably won't have the
       capabilities to route based on location information in the
       near future, but should that timing be considered here?


8.  Security Considerations

   Conveyance of geo-location of a UAC is problematic for many reasons.
   This document calls for that conveyance to normally be accomplished
   through secure message body means (like S/MIME or TLS).  In cases
   where a session set-up is routed based on the location of the UAC
   initiating the session or SIP MESSAGE, securing the location with an
   end-to-end mechanism such as S/MIME is problematic.


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9.  IANA Considerations

   There are no IANA considerations within this document at this time.


10.  Acknowledgements

   To Dave Oran for helping to shape this idea. To Jon Peterson and
   Dean Willis on guidance of the effort.


11. References - Normative

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

 [2] S. Bradner, "Key words for use in RFCs to indicate requirement
     levels," RFC 2119, Mar. 1997.

 [3] H. Schulzrinne, "draft-schulzrinne-sipping-sos-04.txt", Internet
     Draft, Jan 03, Work in progress

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

 [5] J. Polk, J. Schnizlein, M. Linsner, " draft-ietf-geopriv-dhcp-lci-
     option-02.txt", Internet Draft, Aug 2003, Work in progress

 [6] H. Schulzrinne, "draft-schulzrinne-geopriv-dhcp-civil-01.txt",
     Internet Draft, Feb 03, Work in progress

 [7] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk, "draft-
     ietf-geopriv-reqs-03.txt", Internet Draft, Mar 03, Work in
     progress

 [8] J. Rosenberg, "Requirements for Session Policy for the Session
     Initiation Protocol”, draft-ietf-sipping-session-policy-req-00",
     Internet Draft, "work in progress" June, 2003

 [9] C. Jennings, "draft-jennings-sipping-certs-01.txt", Internet
     Draft, "work in progress", July 2003










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12. Author Information

   James M. Polk
   Cisco Systems
   2200 East President George Bush Turnpike
   Richardson, Texas 75082 USA
   jmpolk@cisco.com

   Brian Rosen
   Marconi Communications, Inc.
   2000 Marconi Drive
   Warrendale, PA 15086
   Brian.rosen@marconi.com


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The Expiration date for this Internet Draft is:

April 27th, 2004




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