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Versions: 00 01 02 03 RFC 4538

SIP                                                         J. Rosenberg
Internet-Draft                                             Cisco Systems
Expires: June 22, 2006                                 December 19, 2005


   Request Authorization through Dialog Identification in the Session
                       Initiation Protocol (SIP)
                    draft-ietf-sip-target-dialog-03

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   This Internet-Draft will expire on June 22, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This specification defines the Target-Dialog header field for the
   Session Initiation Protocol (SIP), and the corresponding option tag,
   tdialog.  This header field is used in requests that create SIP
   dialogs.  It indicates to the recipient that the sender is aware of
   an existing dialog with the recipient, either because the sender is
   on the other side of that dialog, or because it has access to the
   dialog identifiers.  The recipient can then authorize the request
   based on this awareness.



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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Overview of Operation  . . . . . . . . . . . . . . . . . . .   4
   3.   UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.   User Agent Server Behavior . . . . . . . . . . . . . . . . .   7
   5.   Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . .   8
   6.   Extensibility Considerations . . . . . . . . . . . . . . . .   8
   7.   Header Field Definition  . . . . . . . . . . . . . . . . . .   8
   8.   Security Considerations  . . . . . . . . . . . . . . . . . .   9
   9.   Relationship with In-Reply-To  . . . . . . . . . . . . . . .   9
   10.  Example Call Flow  . . . . . . . . . . . . . . . . . . . . .  10
   11.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  13
     11.1   Header Field . . . . . . . . . . . . . . . . . . . . . .  13
     11.2   Header Field Parameters  . . . . . . . . . . . . . . . .  13
       11.2.1   local-tag  . . . . . . . . . . . . . . . . . . . . .  13
       11.2.2   remote-tag . . . . . . . . . . . . . . . . . . . . .  13
     11.3   SIP Option Tag . . . . . . . . . . . . . . . . . . . . .  14
   12.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  14
   13.  References . . . . . . . . . . . . . . . . . . . . . . . . .  14
     13.1   Normative References . . . . . . . . . . . . . . . . . .  14
     13.2   Informative References . . . . . . . . . . . . . . . . .  15
        Author's Address . . . . . . . . . . . . . . . . . . . . . .  16
        Intellectual Property and Copyright Statements . . . . . . .  17



























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1.  Introduction

   The Session Initiation Protocol (SIP) [1] defines the concept of a
   dialog as a persistent relationship between a pair of user agents.
   Dialogs provide context, including sequence numbers, proxy routes,
   and dialog identifiers.  Dialogs are established through the
   transmission of SIP requests with particular methods.  Specifically,
   the INVITE, REFER [7] and SUBSCRIBE [2] requests all create dialogs.

   When a user agent receives a request that creates a dialog, it needs
   to decide whether to authorize that request.  For some requests,
   authorization is a function of the identity of the sender, the
   request method, and so on.  However, many situations have been
   identified in which a user agents' authorization decision depends on
   whether the sender of the request is currently in a dialog with that
   user agent, or whether the sender of the request is aware of a dialog
   the user agent has with another entity.

   One such example is call transfer, accomplished through REFER.  If
   user agents A and B are in an INVITE dialog, and user agent A wishes
   to transfer user agent B to user agent C, user agent A needs to send
   a REFER request to user agent B, asking user agent B to send an
   INVITE request to user agent C. User agent B needs to authorize this
   REFER.  The proper authorization decision is that user agent B should
   accept the request if it came from a user with whom B currently has
   an INVITE dialog relationship.  Current implementations deal with
   this by sending the REFER on the same dialog as the one in place
   between user agents A and B. However, this approach has numerous
   problems [10].  These problems include difficulty in determining the
   lifecycle of the dialog and its usages, and difficulties in
   determining which messages are associated with each application
   usage.  Instead, a better approach is for user agent A to send the
   REFER request to user agent B outside of the dialog using its
   Globally Routable User Agent URI (GRUU) [11].  In that case, a means
   is needed for user agent B to authorize the REFER.

   Another example is the application interaction framework [12].  In
   that framework, proxy servers on the path of a SIP INVITE request can
   place user interface components on the user agent that generated or
   received the request.  To do this, the proxy server needs to send a
   REFER request to the user agent, targeted to their GRUU, asking the
   user agent to fetch an HTTP resource containing the user interface
   component.  In such a case, a means is needed for the user agent to
   authorize the REFER.  The appplication interaction framework
   recommends that the request be authorized if it was sent from an
   entity on the path of the original dialog.  This can be done by
   including the dialog identifiers in the REFER, which prove that the
   user agent that sent the REFER is aware of those dialog identifiers



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   (this needs to be secured against eavesdroppers through the sips
   mechanism, of course)

   Another example is if two user agents share an INVITE dialog, and an
   element on the path of the INVITE request wishes to track the state
   of the INVITE.  In such a case, it sends a SUBSCRIBE request to the
   GRUU of the user agent, asking for a subscription to the dialog event
   package.  If the SUBSCRIBE request came from an element on the INVITE
   request path, it should be authorized.

2.  Overview of Operation


                   +--------+            +--------+
                   |        |   INVITE   |        |
                   | Server |----------->| Server |
                   |   A    |            |   B    |
                   |        |...........>|        |
                   +--------+            +--------+
                      ^          REFER     .   \
                     /                      .   \
                    /                        .   \
                   /                          .   \
                  /                            .   \
                 /                              V   V
           +--------+                            +--------+
           |        |                            |        |
           | User   |                            | User   |
           | Agent  |                            | Agent  |
           |   A    |                            |   B    |
           +--------+                            +--------+







                                 Figure 1

   Figure 1 shows the basic model of operation.  User agent A sends an
   INVITE to user agent B, traversing two servers, server A and server
   B. Both servers act as proxies for this transaction.  User B sends a
   200 OK response to the INVITE.  This 200 OK includes a Supported
   header field indicating support for both the GRUU specification
   (through the presence of the gruu option tag) and this specification
   (through the presence of the tdialog option tag).  The 200 OK
   response establishes a dialog between the two user agents.



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   Next, an entity that was present along the request path (server A,
   for example) wishes to send a dialog-forming request (such as REFER)
   requiring to user agent A or B (user B for example).  So, the entity
   acts as a user agent and sends the request to user agent B. This
   request is addressed to the GRUU of user agent B, which server A
   learned from inspecting the Contact header field in the 200 OK of the
   INVITE request.  This GRUU is a URI that can be used by any element
   on the Internet, such as server A, to reach the specific user agent
   instance that generated that 200 OK to the INVITE.

   The request generated by server A will contain a Target-Dialog header
   field.  This header field contains the dialog identifiers for the
   INVITE dialog between user agents A and B, composed of the Call-ID,
   local tag, and remote tag.  Server A knew to include the Target-
   Dialog header field in the REFER request because it knows that user
   agent B supports it.

   When the request arrives at user agent B, it needs to make an
   authorization decision.  Because the INVITE dialog was established
   using a sips URI, and because the dialog identifiers are
   cryptographically random [1], no entity except for user agent A or
   the proxies on the path of the initial INVITE request can know the
   dialog identifiers.  Thus, because the request contains those dialog
   identifiers, user agent B can be certain that the request came from
   either user agent A, the two proxies, or an entity to whom the user
   agent or proxies gave the dialog identifiers.  As such, it authorizes
   the request and performs the requested actions.

3.  UAC Behavior

   A UAC SHOULD include a Target-Dialog header field in a request if the
   following conditions are all true:

   1.  The request is to be sent outside of any existing dialog.

   2.  The user agent client believes that the request may not be
       authorized by the user agent server unless the user agent client
       can prove that it is aware of the dialog identifiers for some
       other dialog.  Call this dialog the target dialog.

   3.  The request does not otherwise contain information that indicates
       that the UAC is aware of those dialog identifiers.

   4.  The user agent client knows that the user agent server supports
       the Target-Dialog header field.  It can know this if it has seen
       a request or response from the user agent server within the
       target dialog that contained a Supported header field which
       included the tdialog option tag.



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   If the fourth condition is not met, the UAC SHOULD NOT use this
   specification.  Instead, if it is currently within a dialog with the
   UAS, it SHOULD attempt to send the request within the existing target
   dialog.

   The following are examples of use cases in which these conditions are
   met:

   o  A REFER request is sent according to the principles of [12].
      These REFER are sent outside of a dialog, and do not contain any
      other information which indicates awareness of the target dialog.
      [12] also mandates that the REFER be sent only if the UA indicates
      support for the target dialog specification.

   o  User A is in separate calls with users B and user C. It decides to
      start a three way call, and so morphs into a focus [15].  User B
      would like to learn the other participants in the conference.  So,
      it sends a SUBSCRIBE request to user A (who is now acting as the
      focus) for the conference event package [14].  It is sent outside
      of the existing dialog between user B and the focus, and would be
      authorized by A if user B could prove that it knows the dialog
      identifiers for its existing dialog with the focus.  Thus, the
      Target-Dialog header field would be include in the SUBSCRIBE.

   The following are examples of use cases in which these conditions are
   not met:

   o  A server acting as a proxy is a participant in an INVITE dialog
      that establishes a session.  The server would like to use the
      Keypad Markup Language (KPML) event package [16] to find out about
      keypresses from the originating user agent.  To do this, it sends
      a SUBSCRIBE request.  However, the Event header field of this
      SUBSCRIBE contains event parameters which indicate the target
      dialog of the subscription.  As such, the request can be
      authorized without additional information.

   o  A server acting as a proxy is a participant in an INVITE dialog
      that establishes a session.  The server would like to use the
      dialog event package [13] to find out about dialogs at the
      originating user agent.  To do this, it sends a SUBSCRIBE request.
      However, the Event header field of this SUBSCRIBE contains event
      parameters which indicate the target dialog of the subscription.
      As such, the request can be authorized without additional
      information.

   Specifications which intend to make use of the Target-Dialog header
   field SHOULD discuss specific conditions in which it is to be
   included.



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   Assuming it is to be included, the value of the call-id production in
   the Target-Dialog header field MUST be equal to the Call-ID of the
   target dialog.  The "remote-tag" header field parameter MUST be
   present, and MUST contain the tag that would be viewed as the remote
   tag from the perspective of the recipient of the new request.  The
   "local-tag" header field parameter MUST be present, and MUST contain
   the tag that would be viewed as the local tag from the perspective of
   the recipient of the new request.

   The request sent by the UAC SHOULD include a Require header field
   that includes the tdialog option tag.  This request should, in
   principle, never fail with a 420 (Bad Extension) response, because
   the UAC would not have sent the request unless it believed the UAS
   supported the extension.  If a Require header field was not included,
   and the UAS didn't support the extension, it would normally reject
   the request becaust it was unauthorized, probably with a 403.
   However, without the Require header field, the UAC would not be able
   to differentiate a 403 that arrived because the UAS didn't actually
   understand the Target-Dialog header field (in which case the client
   should send the request within the target dialog if it can), from a
   403 that arrived because the UAS understood the Target-Dialog header
   field, but elected not to authorize the request despite the fact that
   the UAC proved its awareness of the target dialog (in which case the
   client should not resend the request within the target dialog, even
   if it could).

4.  User Agent Server Behavior

   If a user agent server receives a dialog-creating request, and wishes
   to authorize the request, and that authorization depends on whether
   or not the sender has knowledge of an existing dialog with the UAS,
   and information outside of the Target-Dialog header field does not
   provide proof of this knowledge, the UAS SHOULD check the request for
   the existence of the Target-Dialog header field.  If this header
   field is not present, the UAS MAY still authorize the request based
   on other means.

   If the header field is present, and the value of the call-id
   production, the "remote-tag" and "local-tag" values match the
   Call-ID, remote tag and local tag of an existing dialog, and the
   dialog that they match was established using a sips URI, the UAS
   SHOULD authorize the request if it would authorize any entity on the
   path of the request that created that dialog, or any entity trusted
   by an entity on the path of the request that created that dialog.

   If the dialog identifiers match, but they match a dialog not created
   with a sips URI, the UAS MAY authorize the request if it would
   authorize any entity on the path of the request that created that



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   dialog, or any entity trusted by an entity on the path of the request
   that created that dialog.  However, in this case, any eavesdropper on
   the original dialog path would have access to the dialog identifiers,
   and thus the authorization is optional.

   If the dialog identifiers don't match, or if they don't contain both
   a "remote-tag" and "local-tag" parameter, the header field MUST be
   ignored, and authorization MAY be determined by other means.

5.  Proxy Behavior

   Proxy behavior is unaffected by this specification.

6.  Extensibility Considerations

   This specification depends on a user agent client knowing, ahead of
   sending a request to a user agent server, whether or not that user
   agent server supports the Target-Dialog header field.  As discussed
   in Section 3, the UAC can know this because it saw a request or
   response sent by that UAS within the target dialog that contained the
   Supported header field whose value included the tdialog option tag.

   Because of this requirement, it is especially important that user
   agents compliant to this specification include a Supported header
   field in all dialog forming requests and responses.  Inclusion of the
   Supported header fields in requests is at SHOULD strength within RFC
   3261.  This specification does not alter that requirement.  However,
   implementors should realize that, unless the tdialog option tag is
   placed in the Supported header field of requests and responses, this
   extension is not likely to be used, and instead, the request is
   likely to be resent within the existing target dialog (assuming the
   sender is the UA on the other side of the target dialog).  As such,
   the conditions in which the SHOULD would not be followed would be
   those rare cases in which the UA does not want to enable usage of
   this extension.

7.  Header Field Definition

   The grammar for the Target-Dialog header field is defined as follows:


   Target-Dialog      =     "Target-Dialog" HCOLON call-id *(SEMI
                            td-param)
   td-param           =     remote-param / local-param / generic-param
   remote-param       =     "remote-tag" EQUAL token
   local-param        =     "local-tag" EQUAL token

   Figure 3 and Figure 4 are an extension of Tables 2 and 3 in RFC 3261



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   [1] for the Target-Dialog header field.  The column "INF" is for the
   INFO method [3], "PRA" is for the PRACK method [4], "UPD" is for the
   UPDATE method [5], "SUB" is for the SUBSCRIBE method [2], "NOT" is
   for the NOTIFY method [2], "MSG" is for the MESSAGE method [6], "REF"
   is for the REFER method [7], and "PUB" is for the PUBLISH method [8].


   Header field          where  proxy  ACK BYE CAN INV OPT REG PUB

   Target-Dialog           R      ar    -   -   -   o   -   -   -

                Figure 3: Allowed Methods for Target-Dialog



   Header field          where  proxy  PRA UPD SUB NOT INF MSG REF
   Target-Dialog           R      ar    -   -   o   -   -   -   o

                Figure 4: Allowed Methods for Target-Dialog


8.  Security Considerations

   The Target-Dialog header field is used to authorize requests based on
   the fact that the sender of the request has access to information
   that only certain entities have access to.  In order for such an
   authorization decision to be secure, two conditions have to be met.
   Firstly, no eavesdroppers can have access to this information.  That
   requires the original SIP dialog to be established using a sips URI,
   which provides TLS on each hop.  With a sips URI, only the user
   agents and proxies on the request path will be able to know the
   dialog identifiers.  The second condition is that the dialog
   identifiers be cryptographically random that they cannot be guessed.
   RFC 3261 requires global uniquess for the Call-ID and 32 bits of
   cryptographic randomness for each tag (there are two tags for a
   dialog).  Given the short duration over which a typical dialog exists
   (perhaps as long as a day), this amount of randomness appears
   adequate to prevent guessing attacks.  However, its important to note
   that this specification truly requires cryptographic randomness, as
   opposed to just pseudorandom identifiers.  Pseudorandom identifiers
   reduce the probability of collision, but because they are guessable,
   they are not sufficient to prevent an attacker from observing a
   sequence of identifiers, guessing the next one, and then using this
   specification to launch an attack.

9.  Relationship with In-Reply-To

   RFC 3261 defines the In-Reply-To header field.  It provides a list of



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   Call-IDs for calls that the current request references or returns.
   It was meant to serve a similar purpose as the Reply-To in email; to
   faciliate in the construction of "threads" of conversations in a user
   interface.  Target-Dialog is similar, in that it also references a
   previous session.  Due to their similarities, it is important to
   understand the differences, as these two header fields are not
   substitutes for each other.

   Firstly, In-Reply-To is meant for consumption by a human or a user
   interface widget, for providing the user with a context that allows
   them to decide what a call is about and whether they should take it.
   Target-Dialog, on the other hand, is meant for consumption by the
   user agent itself, to facilitate authorization of session requests in
   specific cases where authorization is not a function of the user, but
   rather the underlying protocols.  A UA will authorize a call
   containing Target-Dialog based on a correct value of the Target-
   Dialog header field.

   Secondly, Target-Dialog references a specific dialog which must be
   currently in progress.  In-Reply-To references a previous call
   attempt, most likely one that did not result in a dialog.  This is
   why In-Reply-To uses a Call-ID, and Target-Dialog uses a set of
   dialog identifiers.

   Finally, In-Reply-To implies cause and effect.  When In-Reply-To is
   present, it means that the request is being sent because of the
   previous request that was delivered.  Target-Dialog does not imply
   cause-and-effect, merely awareness for the purposes of authorization.

10.  Example Call Flow

   In this example, user agent A and user agent B establish an INVITE
   initiated dialog through Server-A and Server-B, each of which acts as
   a proxy for the INVITE.  Server B would then like to use the app
   interaction framework [12] to request user agent A to fetch an HTML
   user interface component.  To do that, it sends a REFER request to
   A's GRUU.  The flow for this is shown in Figure 5.  The conventions
   of [17] are used to describe representation of long message lines.













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             A        Server-A     Server-B         B
             |(1) INVITE  |            |            |
             |----------->|            |            |
             |            |(2) INVITE  |            |
             |            |----------->|            |
             |            |            |(3) INVITE  |
             |            |            |----------->|
             |            |            |(4) 200 OK  |
             |            |            |<-----------|
             |            |(5) 200 OK  |            |
             |            |<-----------|            |
             |(6) 200 OK  |            |            |
             |<-----------|            |            |
             |(7) ACK     |            |            |
             |------------------------------------->|
             |            |(8) REFER   |            |
             |            |<-----------|            |
             |(9) REFER   |            |            |
             |<-----------|            |            |
             |(10) 200 OK |            |            |
             |----------->|            |            |
             |            |(11) 200 OK |            |
             |            |----------->|            |


                                 Figure 5

   First, the caller sends an INVITE, as shown in message 1.


   INVITE sips:B@example.com SIP/2.0
   Via: SIP/2.0/TLS host.example.com;branch=z9hG4bK9zz8
   From: Caller <sip:A@example.com>;tag=kkaz-
   To: Callee <sip:B@example.org>
   Call-ID: fa77as7dad8-sd98ajzz@host.example.com
   CSeq: 1 INVITE
   Max-Forwards: 70
   Supported: gruu, tdialog
   Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, REFER
   Accept: application/sdp, text/html
   <allOneLine>
   Contact: <sips:A@example.com;opaque=urn:uuid:f81d4f
   ae-7dec-11d0-a765-00a0c91e6bf6;grid=99a>;schemes="http,sip,sips"
   </allOneLine>
   Content-Length: ...
   Content-Type: application/sdp

   --SDP not shown--



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   The INVITE indicates that the caller supports GRUU (note its presence
   in the Contact header field of the INVITE) and the Target-Dialog
   header field.  This INVITE is forwarded to the callee (messages 2-3),
   which generates a 200 OK response that is forwarded back to the
   caller (message 4-5).  Message 5 might look like:


   SIP/2.0 200 OK
   Via: SIP/2.0/TLS host.example.com;branch=z9hG4bK9zz8
   From: Caller <sip:A@example.com>;tag=kkaz-
   To: Callee <sip:B@example.org>;tag=6544
   Call-ID: fa77as7dad8-sd98ajzz@host.example.com
   CSeq: 1 INVITE
   Contact: <sips:B@pc.example.org>
   Content-Length: ...
   Content-Type: application/sdp

   --SDP not shown--

   In this case, the called party does not support GRUU or the Target-
   Dialog header field.  The caller generates an ACK (message 7).
   Server B then decides to send a REFER to user A:


   <allOneLine>
   REFER sips:A@example.com;opaque=urn:uuid:f81d4f
   ae-7dec-11d0-a765-00a0c91e6bf6;grid=99a SIP/2.0
   </allOneLine>
   Via: SIP/2.0/TLS serverB.example.org;branch=z9hG4bK9zz10
   From: Server B <sip:serverB.example.org>;tag=mreysh
   <allOneLine>
   To: Caller <sips:A@example.com;opaque=urn:uuid:f81d4f
   ae-7dec-11d0-a765-00a0c91e6bf6;grid=99a>
   </allOneLine>
   Target-Dialog: fa77as7dad8-sd98ajzz@host.example.com
     ;local-tag=kkaz-
     ;remote-tag=6544
   Refer-To: http://serverB.example.org/ui-component.html
   Call-ID: 86d65asfklzll8f7asdr@host.example.com
   CSeq: 1 REFER
   Max-Forwards: 70
   Require: tdialog
   Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, NOTIFY
   Event: refer
   Contact: <sips:serverB.example.org>
   Content-Length: 0

   This REFER will be delivered to server A because it was sent to the



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   GRUU.  From there, it is forwarded to user agent A (message 9), and
   authorized because of the presence of the Target-Dialog header field.

11.  IANA Considerations

   This specification registers a new SIP header field, and a new option
   tag according to the processes of RFC 3261 [1], and two new header
   field parameters according to the processes of RFC 3968 [9].

11.1  Header Field

   RFC Number: RFC XXXX [Note to IANA: Fill in with the RFC number of
      this specification.]

   Header Field Name: Target-Dialog

   Compact Form: none


11.2  Header Field Parameters

   This section registers two header field parameters according to the
   processes of RFC 3968 [9].

11.2.1  local-tag

   Header Field: Target-Dialog

   Header Field Parameter: local-tag

   Predefined Values: None

   RFC: RFC XXXX [Note to IANA: Fill in with the RFC number of this
      specification.]


11.2.2  remote-tag

   Header Field: Target-Dialog

   Header Field Parameter: remote-tag

   Predefined Values: None

   RFC: RFC XXXX [Note to IANA: Fill in with the RFC number of this
      specification.]





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11.3  SIP Option Tag

   This specification registers a new SIP option tag per the guidelines
   in Section 27.1 of RFC 3261.

   Name: tdialog

   Description: This option tag is used to identify the target dialog
      header field extension.  When used in a Require header field, it
      implies that the recipient needs to support the Target-Dialog
      header field.  When used in a Supported header field, it implies
      that the sender of the message supports it.


12.  Acknowledgments

   This specification is based on a header field first proposed by
   Robert Sparks in the dialog usage draft.  John Elwell provided
   helpful comments.

13.  References

13.1  Normative References

   [1]  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.

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

   [3]  Donovan, S., "The SIP INFO Method", RFC 2976, October 2000.

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

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

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

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

   [8]  Niemi, A., "Session Initiation Protocol (SIP) Extension for



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        Event State Publication", RFC 3903, October 2004.

   [9]  Camarillo, G., "The Internet Assigned Number Authority (IANA)
        Header Field Parameter Registry for the Session Initiation
        Protocol (SIP)", BCP 98, RFC 3968, December 2004.

13.2  Informative References

   [10]  Sparks, R., "Multiple Dialog Usages in the Session Initiation
         Protocol", draft-sparks-sipping-dialogusage-00 (work in
         progress), July 2004.

   [11]  Rosenberg, J., "Obtaining and Using Globally Routable User
         Agent (UA) URIs (GRUU) in the  Session Initiation Protocol
         (SIP)", draft-ietf-sip-gruu-05 (work in progress),
         September 2005.

   [12]  Rosenberg, J., "A Framework for Application Interaction in the
         Session Initiation Protocol  (SIP)",
         draft-ietf-sipping-app-interaction-framework-05 (work in
         progress), July 2005.

   [13]  Rosenberg, J., "An INVITE Inititiated Dialog Event Package for
         the Session Initiation  Protocol (SIP)",
         draft-ietf-sipping-dialog-package-06 (work in progress),
         April 2005.

   [14]  Rosenberg, J., "A Session Initiation Protocol (SIP) Event
         Package for Conference State",
         draft-ietf-sipping-conference-package-12 (work in progress),
         July 2005.

   [15]  Rosenberg, J., "A Framework for Conferencing with the Session
         Initiation Protocol",
         draft-ietf-sipping-conferencing-framework-05 (work in
         progress), May 2005.

   [16]  Burger, E., "A Session Initiation Protocol (SIP) Event Package
         for Key Press Stimulus  (KPML)", draft-ietf-sipping-kpml-07
         (work in progress), December 2004.

   [17]  Sparks, R., "Session Initiation Protocol Torture Test
         Messages", draft-ietf-sipping-torture-tests-07 (work in
         progress), May 2005.







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Author's Address

   Jonathan Rosenberg
   Cisco Systems
   600 Lanidex Plaza
   Parsippany, NJ  07054
   US

   Phone: +1 973 952-5000
   Email: jdrosen@cisco.com
   URI:   http://www.jdrosen.net








































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