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Versions: (draft-polk-geopriv-dhcp-lbyr-uri-option) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 19

Geopriv WG                                                   James Polk
Internet-Draft                                            Cisco Systems
Intended status:  Standards Track (PS)                    July 13, 2009
Expires: January 13, 2010


        Dynamic Host Configuration Protocol (DHCP) IPv4 and IPv6
         Option for a Location Uniform Resource Identifier (URI)
              draft-ietf-geopriv-dhcp-lbyr-uri-option-05

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Legal

   This documents and the information contained therein are provided on
   an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
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Abstract

   This document creates a Dynamic Host Configuration Protocol (DHCP)
   Option for the downloading of a Location Uniform Resource Identifier
   (URI) of a client, to be dereferenced in a separate transaction.
   Once the location URI is received by an endpoint, it can be
   dereferenced by the client to learn its geographic location, or sent
   to another entity to learn this client's location.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Format of the DHCP LuriElement Option . . . . . . . . . . . .  5
       2.1.  Overall Format of LuriElement Option in IPv4  . . . . .  5
       2.2.  Overall Format of LuriElement Option in IPv6  . . . . .  5
       2.3.  LuriElement Format for both IPv4 and IPv6 . . . . . . .  6
   3.  DHC Option Operation  . . . . . . . . . . . . . . . . . . . .  7
       3.1 Architectural Assumptions . . . . . . . . . . . . . . . .  8
       3.2 Harmful URIs and URLs . . . . . . . . . . . . . . . . . .  9
       3.3 Valid Location URI Schemes or Types . . . . . . . . . . .  9
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . 11
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 12
       7.1. Normative References . . . . . . . . . . . . . . . . . . 12
       7.2. Informative References . . . . . . . . . . . . . . . . . 13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 13


   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].








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1.  Introduction

   This document creates a Dynamic Host Configuration Protocol (DHCP)
   Option for the downloading of a Location Uniform Resource Identifier
   (URI) of a client, to be dereferenced in a separate transaction.
   A client, for example, can be a Session Initiation Protocol (SIP)
   User Agent (UA)  [RFC3261] (i.e., a Phone).  This location URI
   points a Location Server [ID-LBYR-REQ] which has the geolocation of
   the client (through means not defined in this document).

   The Location Server stores the Target's location a presence
   document, called a Presence Information Date Format - Location
   Object (PIDF-LO).  Once a client attains this location URI, an
   application on the target can either dereference the URI to receive
   its PIDF-LO, or it can convey this location URI instead of conveying
   the location value in a message.  Having a location URI has
   advantages over having a PIDF-LO, especially when a target's
   location changes.  With a location URI, when a target moves, the
   location URI does not. It can still be given out as the Target's
   location. The opposite is true if the location is conveyed by value
   in a message. Once the Target moves, the previously given location
   is no longer valid, and it the Target wants to inform another entity
   about its location, it has to send the PIDF-LO to the location
   recipient (again).

   The act of dereferencing location from a location URI is explained
   in [ID-SIP-LOC], which shows how a Location Recipient of a location
   URI subscribes to a Location Server to attain the location of the
   Target. If the dereferencer has permission, defined in [ID-GEO-POL],
   the location of the target will be received.  The Location Server
   (LS) will grant permission to location inquires based on the rules
   established by a Rule Holder [RFC3693].  The Location Server has the
   ability to challenge any request of a target's location, thereby
   providing additive security properties before location revelation.

   There are use-cases, such as calling the appropriate Pizza Hut
   without having to look up in a directory which store is closest,
   where a UA knowing its location can call a
   main/national/international Pizza Hut number or address and let the
   UA's location tell Pizza Hut enough information to have them
   route/retarget the SIP request to the appropriate store within the
   Pizza Hut organization to deliver the pizza to the caller's
   location.

   A problem exists within existing RFCs that provide location to the
   UA ([RFC3825] and [RFC4776]), these DHCP Options for geolocation
   require an update of the entire location information (LI) every time
   a client moves.  Not all clients will move frequently, but some
   will.  Refreshing location every time a client moves does not scale
   in certain networks/environments, such as IP based cellular
   networks, enterprise networks or service provider networks with
   mobile endpoints.  An 802.11 based access network is one example of


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   this. Constantly updating LCI to endpoints might not scale in mobile
   (residential or enterprise or municipal) networks in which the
   client is moving through more than one network attachment point,
   perhaps as a person walks or drives with their endpoint down a
   neighborhood street or apartment complex or a shopping center.

   If the client were provided a location URI reference to retain and
   hand out when it wants or needs to convey its location (in a
   protocol other than DHCP), a location URI that would not change as
   the client's location changes (within a domain), scaling issues
   would be significantly reduced to needing an update of the location
   URI only when a client changes administrative domains - which is
   much less often.  This delivery of an indirect location has the
   added benefit of not using up valuable or limited bandwidth to the
   client with the constant updates.  It also relieves the client from
   having to determine when it has moved far enough to consider asking
   for a refresh of its location.

   In enterprise networks, if a known location is assigned to each
   individual Ethernet port in the network, a device that attaches to
   the network a wall-jack (directly associated with a specific
   Ethernet Switch port) will be associated with a known location via a
   unique circuit-ID that's used by the RAIO Option defined in RFC 3046
   [RFC3046].  This assumes wall-jacks have an updated wiremap
   database.  RFC 3825 and RFC 4776 would return an LCI value of
   location.  This document specifies how a location URI is returned
   using DHCP.  Behind the DHCP server, in the backend of the network,
   via the (logical entity of an) LS has a PIDF-LO to be dereferenced
   with a location URI.

   If local configuration has the requirement of only assigning unique
   location URIs to each client, then unique LbyRs will be given out,
   though they will all have the same location at the record, relieving
   the backend Sighter from individually maintaining each location
   independently.

   This Option can be useful in WiMAX connected endpoints or IP
   cellular endpoints.  The location URI Option can be configured as a
   client if there is a router, such as a residential home gateway,
   with the ability to communicate to downstream endpoints as a server.

   How an LS challenges a dereference can vary, and a policy
   established by a rulemaker [RFC3693] for a Location Target as to
   what type of challenge(s) is to be used, how strong a challenge is
   used or how precise the location information is given to a
   requestor. All of this is outside the scope of this document (since
   this will not be accomplished using DHCP).

   This document IANA registers the new IPv4 and IPv6 DHC Options for a
   location URI.




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2.  Format of the DHCP LuriElement Option

2.1 Overall Format of LuriElement Option in IPv4

   The LuriElement Option format for IPv4 is as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Code XXX    |   Length=XX   |  Ver  | Resv  |               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               .
    .                         LuriElements...                      ...
    .                  (see section 2.3 for details) ...            .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 1. IPv4 Fields for this LuriElement Option

   Code XXX:  The code for this DHCPv4 option (IANA assigned).

   Length=XX: The length of this option, counted in bytes - not
              counting the Code and Length bytes. This is a variable
              length Option, therefore the length value will change
              based on the length of the LbyR within the Option.

   Ver:       (4 bits) The version of this Option. This document
              defines version 1 of this Option.

   Resv:      (4 bits) reserved for future use.

   LuriElement: see section 2.3 for details


2.2 Overall Format of LuriElement Option in IPv6

   The LuriElement Option format for IPv6 is as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          option-code          |           option-len          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Ver  | Resv  |                                               .
    +---------------+                                               .
    .                        LuriElements...                        .
    .                 (see section 2.3 for details)                 .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 2. IPv6 fields of this LuriElement Option

   option-code: The code for this DHCPv6 option (IANA assigned).

   option-len:  The length of this option, counted in bytes - not


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                counting the Code and Length bytes. This is a variable
                length Option, therefore the length value will change
                based on the shape within the Option.

   Ver:         See above (Section 2.1). This will specify version 1.

   Resv:        See above (Section 2.1).

   LuriElement: see below (Section 2.3 for details).


2.3 LuriElement Format for both IPv4 and IPv6

   The LuriElement, in both DHCPv4 and DHCPv6, have the following
   format:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    LuriType    |   LuriLength   |   LuriValue                ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 3. LuriElement Format for both IPv4 and IPv6


      LuriType:   A one-byte identifier of the data location value.

      LuriLength: The length, in bytes, of the LuriValue, not including
                  the LuriLength field itself, up to a maximum of 255
                  bytes.

      LuriValue:  The LuriElement value, as described in detail below.
                  The LuriValue is always in UTP-8.

   The LuriTypes this document defines (and IANA registers) for a point
   are:

      LuriType=1 Location URI - This is the URI pointing at the
                 location record where the PIDF-LO resides which
                 indicates the location of the Location Target.

      LuriType=2 Valid-For - The time, in seconds, this URI is to be
                 considered Valid for dereferencing. The timer
                 associated with this LuriType starts upon receipt of
                 this Option.

   The LuriType=2 (Valid-For) indicates how long, in seconds, the
   client is to consider this LuriType=1 (location URI) valid
   before performing a refresh of this Option, with a refreshed
   LuriType=2 (Valid-For) value.  A refresh MAY be done merely at the
   normal DHCP refresh rate, or necessitated by this timer, perhaps
   with the client only requesting this Option be refreshed.


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   It is RECOMMENDED when the counter associated with this LuriType=2
   (Valid-For) value has passed, the client perform a refresh of this
   Option.  For example, if 16000 was the initial value of the
   LuriType=2 (Valid-For) value, when 8000 seconds have passed, the
   Option SHOULD be refreshed.

   The LuriType=2 (Valid-For) is not mandated for use by this document.
   However, its presence MUST NOT cause any error in handling the
   location URI (i.e., if not understood, it MUST be ignored).

   This Option format is highly extensible. Additional LuriType types
   created MUST be done so through IANA registration with peer review
   and an RFC.


3. DHC Option Operation

   The [RFC3046] RAIO MUST be utilized to provide the appropriate
   indication to the DHCP Server where this DISCOVER or REQUEST message
   came from, in order to supply the correct response.  That said, this
   Option SHOULD NOT be in a DISCOVER message, because there is zero
   knowledge by the client of which Server will answer.

   Caution SHOULD always be used involving the creation of large
   Options, meaning that this Option MAY need to be in its own INFORM,
   OPTION or ACK message.

   It is RECOMMENDED to avoid building URIs, with any parameters,
   larger than what a single DHCP response can be.  However, if a
   message is larger than 255 bytes, concatenation is allowed, per RFC
   3396 [RFC3396].

   Per [RFC2131], subsequent LuriElement Options, which are
   non-concatenated, overwrite the previous value.

   location URIs MUST NOT reveal identity information of the user of
   the device, since DHCP is a cleartext delivery protocol. For
   example, location URIs such as

      sips:34LKJH534663J54@example.com

   SHOULD be done, providing no identity information, rather than a
   location URI such as this

      sips:aliceisinatlanta@example.com

   In the <presence> element of the PIDF-LO there is an entity=
   attribute that identities the target of *this* location.  It is up
   to the PIDF-LO generator, either Location Server or an application
   in the endpoint, to insert the identity in the entity= attribute.
   This can be seen in [RFC4119].  The entity= discussion is orthogonal


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   to the identification information contained within the location URI.

   This Option is only for communications between a DHCP client and a
   DHCP server.  It can be solicited (requested) by the client, or it
   can be pushed by the server without a request for it.  DHCP Options
   not understood are ignored.  A DHCP server might or might not have
   the location of a client, therefore direct knowledge of a
   location URI within the server.  If a server does not have a
   client's location, a communication path (or request) to an LS would
   be necessary.

   Further, any location revelation rules and policies a user has
   regarding the treatment of their actual location, and who can
   access (what precision of) their location will be done with a
   protocol other than DHCP, and likely will be done before anything
   other than default authentication and authorization permissions are
   used when a Location Recipient requests for a Target's location.

   Differentiating clients is done via client identifiers.  Therefore,
   in many implementations, each client can be assigned unique location
   URIs, though this is not mandatory.

   Any dereferencing of a client's location URI would not involve DHCP
   as well, but more likely by an application layer protocol such as
   SIP, through a subscription to the location URI on the LS. The LS
   would also handle all authentication and authorization of location
   requests, which is also not performed with DHCP, therefore not
   defined here.

   In the case of residential gateways being DHCP servers, they usually
   perform as DHCP clients in a hierarchical fashion up into a service
   provider's network DHCP server(s), or learn what information to
   provide via DHCP to residential clients through a protocol such as
   PPP.  In these cases, the location URI would likely indicate the
   residence's civic address to all wired or wireless clients within
   that residence.  This is not inconsistent with what's stated above.


3.1 Architectural Assumptions

   The following assumptions have been made for use of this LuriElement
   Option for a client to learn its location URI (in no particular
   order):

   o  Any user control (what [RFC3693] calls a 'ruleholder') for the
      parameters and profile options a Location Object will have is out
      of scope of this document, but assumed to take place via an
      external web interface between the user and the Location Server
      (direct or indirect).  Some of this is described in [ID-GEO-POL].

   o  The authorization vs. possession security model can be found in
      [ID-LBYR-REQ], describing what is expected in each model of


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      operation.  It should be assumed that a location URI attained
      using DHCP will operate under an authorization model. This means
      possessing the location URI does not give that entity the right
      to view the PIDF-LO of the target whose location is indicated in
      a presence document.  The dereference transaction will be, in
      many environments, challenged by the Location Server.  The nature
      of this challenge is out of scope of this document.

   o  This document does not prevent some environments from operating
      in a possession model, for example - tightly controlled
      enterprise networks, but this operation SHOULD NOT be assumed to
      exist as a matter of local policy. The costs associated with
      authorization vs. possession models are discussed in section
      3.3.2 of [ID-GEO-RA].


3.2 Harmful URIs and URLs

   There are, in fact, some types of URIs that are not good to receive,
   due to security concerns.  For example, any URLs that can have
   scripts, such as "data:" URLs, and some "HTTP:" URLs that go to web
   pages that have scripts.  Therefore,

   o URIs received via this Option SHOULD NOT be sent to a
     general-browser to connect to a web page, because they could have
     harmful scripts.

   o This Option SHOULD NOT contain "data:" URLs, because they could
     contain harmful scripts.

   Instead of listing all the types of URIs and URLs that can be
   misused or potentially have harmful affects, Section 3.3 IANA
   registers acceptable location URI schemes (or types).


3.3  Valid Location URI Schemes or Types

   This section specifies which URI types are acceptable as a location
   URI scheme (or type) for this DHCP Option:

   1. sip:
   2. sips:
   3. pres:

   These location URI types are IANA registered in section 4.2 of this
   document.








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4.  IANA Considerations

4.1 The IPv4 Option number for this Option

   This document IANA registers this IPv4 Option number XXX (to be
   assigned by IANA once this document becomes an RFC).


4.2 The IPv6 Option-Code for this Option

   This document IANA registers this IPv6 Option-Code XXX (to be
   assigned by IANA once this document becomes an RFC).


4.3 The Version number for this Option

   This document IANA registers the version number 1 of this Option.


4.4 IANA Considerations for Acceptable Location URI Types

   IANA is requested to create a new registry for acceptable location
   URI types.

   The following 3 URI types are registered by this document:

   1. sip:
   2. sips:
   3. pres:

   Any additional location URI types to be defined for use via
   this DHC Option need to be created and IANA registered with peer
   review and an RFC.

4.5 IANA Considerations for LuriTypes

   IANA is requested to create a new registry for acceptable location
   types defined in section 3.2 of this document, arranged similar to
   this:

   +------------+----------------------------------------+-----------+
   |  LuriType  |   Name                                 | Reference |
   +------------+----------------------------------------+-----------+
   |     1      |   Location URI                         | RFC XXXX* |
   |     2      |   Valid-For                            | RFC XXXX* |
   +------------+----------------------------------------+-----------+

    * RFC XXXX is to be replaced with this document's RFC-Editor RFC
      number.

   Additions to this list require a standards track RFC.



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5.  Security Considerations

   Where critical decisions might be based on the value of this
   location URI option, DHCP authentication in [RFC3118] SHOULD be used
   to protect the integrity of the DHCP options.

   A real concern with RFC 3118 it is that not widely deployed because
   it requires pre-shared keys to successfully work (i.e., in the
   client and in the server).  Most implementations do not
   accommodate this.

   DHCP is a broadcast initially (a client looking for a server),
   unicast response (answer from a server) type of protocol.  It is not
   secure in a practical sense.  In today's infrastructures, DHCP will
   be primarily used over a wired, switched Ethernet network, requiring
   physical access to within a wire to gain access.  Further, within an
   802.11 wireless network, the 802.11 specs have layer 2 security
   mechanisms in place to help prevent a location URI from being
   learned by an unauthorized entity.

   That said, having the location URI does not mean an unauthorized
   entity has the location of a client.  The location URI still needs
   to be dereferenced to learn the location of the client.  This
   dereferencing function, which is not done using DHCP, is done by
   requesting the location record at a Location Server, which is a
   defined entity built to challenge each request it receives based on
   a joint policy of what is called a rulemaker.  The ruleholder, as
   defined in RFC 3693, configures the authentication and authorization
   policies for the location revelation of a Target.  This includes
   giving out more or less precise location information in a response,
   therefore it can answer a bad-hat, but not allow it from learning
   exactly where a client is.  The rulemaker, which is a combination of
   the default rules set up by the location provider and those decided
   on by the user of the Target device.  Likely, the rules the user
   wants will not be allowed to go past some limits established by the
   location provider, i.e., the administrator of the LS, for various
   capability or security reasons.

   Penetrating an LS is supposed to be hard, and hopefully vendors that
   implement an LS accomplish this goal.

   It is envisioned, as stated in the text above, as described both in
   [ID-LBYR-REQ] and [ID-GEO-RA], this Option MUST be assumed to
   operate under an authorization model, vs. a much more open
   possession model.  This model choice is not strictly enforced, but
   implementations (in the text above) have been advised to build with
   this in mind.

   As to the concerns about the location URI itself, as stated in the
   document here (in Section 3.), it MUST NOT have any user identifying
   information in the URI user-part/string itself.  The location URI


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   also needs to be hard to guess that it belongs to a specific user.
   There is some debate as to whether this location URI need be a
   random alphanumeric string or just unique.  If the latter, there is
   some debate as to the how we define unique. Is that through space
   and time, as RFC 3261 defines a SIP Call-ID needs to be (meaning:
   never a duplicate, ever, by any device, ever)? Or is it unique to
   within a specific domain for as long as it is actively assigned to a
   client (plus some interval).

   When implementing a DHC server that will serve clients across an
   uncontrolled network, one should consider the potential security
   risks therein.


6.  Acknowledgements

   Thanks to James Winterbottom, Marc Linsner, Roger Marshall and
   Robert Sparks for their useful comments. And to Lisa Dusseault for
   her concerns about the types of URIs that can cause harm.  To
   Richard Barnes for inspiring a more robust Security Considerations
   section.  To Hannes Tschofenig and Ted Hardie for riding me to
   comply with their concerns.


7.  References

7.1.  Normative References

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

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

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

 [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
           Messages", RFC 3118, June 2001.

 [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.

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

 [RFC3396] T. Lemon, S. Cheshire, "Encoding Long Options in the Dynamic
           Host Configuration Protocol (DHCPv4)", RFC 3396, November
           2002




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


7.2.  Informative References

 [ID-SIP-LOC] J. Polk, B. Rosen, "SIP Location Conveyance", "work in
           progress", July 2009

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

 [RFC4776] H. Schulzrinne, " Dynamic Host Configuration Protocol
           (DHCPv4 and DHCPv6) Option for Civic Addresses Configuration
           Information ", RFC 4776, November 2006

 [ID-LBYR-REQ] R. Marshall, "Requirements for a Location-by-Reference
           Mechanism", "work in progress", Feb 2009

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

 [ID-GEO-POL] H. Schulzrinne, H. Tschofenig, J. Morris, J. Cuellar, J.
           Polk, "Geolocation Policy: A Document Format for Expressing
           Privacy Preferences for Location Information", "work in
           progress", Feb 2009

 [ID-GEO-RA] J. Peterson, T. Hardie, J. Morris, " Implications of
           'retransmission-allowed' for SIP Location Conveyance",
           "work in progress", March 2009


Authors' Address

   James Polk
   3913 Treemont Circle
   Colleyville, Texas 76034
   USA

   Email: jmpolk@cisco.com













Polk                   Expires January 13, 2010               [Page 13]


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