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Versions: 00 01 02 03 04 RFC 4488

SIP                                                             O. Levin
Internet-Draft                                     Microsoft Corporation
Expires: April 17, 2005                                 October 17, 2004


                Suppression of REFER Implicit Subscription
                 draft-ietf-sip-refer-with-norefersub-00

Status of this Memo

    This document is an Internet-Draft and is subject to all provisions
    of section 3 of RFC 3667.  By submitting this Internet-Draft, each
    author represents that any applicable patent or other IPR claims of
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    which he or she become aware will be disclosed, in accordance with
    RFC 3668.

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    This Internet-Draft will expire on April 17, 2005.

Copyright Notice

    Copyright (C) The Internet Society (2004).

Abstract

    This specification defines the way to suppress an implicit
    subscription with REFER method in SIP.









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Table of Contents

    1.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   3
    2.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   4
    3.   Motivation . . . . . . . . . . . . . . . . . . . . . . . . .   5
    4.   Definition . . . . . . . . . . . . . . . . . . . . . . . . .   6
    5.   Preventing Forking of REFER Requests . . . . . . . . . . . .   7
    6.   Example  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
    7.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .   9
    8.   Security Considerations  . . . . . . . . . . . . . . . . . .  10
    9.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  11
    10.  References . . . . . . . . . . . . . . . . . . . . . . . . .  12
    10.1   Normative References . . . . . . . . . . . . . . . . . . .  12
    10.2   Informational References . . . . . . . . . . . . . . . . .  12
         Author's Address . . . . . . . . . . . . . . . . . . . . . .  12
         Intellectual Property and Copyright Statements . . . . . . .  13



































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1.  Terminology

    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 RFC 2119 [1].

    To simplify discussions of the REFER method and its extensions, three
    new terms are being used throughout the document:
    o  REFER-Issuer: the UA issuing the REFER request
    o  REFER-Recipient: the UA receiving the REFER request
    o  REFER-Target: the UA designated in the Refer-To URI








































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2.  Introduction

    The REFER specification specifies that every REFER creates an
    implicit subscription between the REFER-Issuer and the
    REFER-Recipient.  This document defines a new option tag,
    "norefersub", which specifies that an implicit subscription for event
    package refer should not be created as a result of accepting this
    REFER request.











































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3.  Motivation

    The REFER specification mandates that every REFER creates an implicit
    subscription between the REFER-Issuer and the REFER-Recipient.  This
    subscription results in at least one NOTIFY being sent from the
    REFER-Recipient to the REFER-Issuer.  The REFER-Recipient may choose
    to cancel the implicit subscription with this NOTIFY.  The
    REFER-Issuer may choose to cancel this implicit subscription with an
    explicit SUBSCRIBE (Expires: 0) after receipt of the initial NOTIFY
    or by sending a 481 response to this initial NOTIFY request.

    One purpose of requiring the implicit subscription and initial NOTIFY
    is to allow for the situation where the REFER request gets forked and
    the REFER-Issuer needs a way to see the multiple dialogs that may be
    established as a result of the forked REFER.  This is the same
    approach used to handle forking of SUBSCRIBE [4] requests.  Where the
    REFER-Issuer explicitly specifies that forking not occur, the
    requirement that an implicit subscription be established is
    unnecessary.

    Another purpose of the NOTIFY is to inform the REFER-Issuer of the
    progress of the SIP transaction that results from the REFER at the
    REFER-Recipient.  In the case where the REFER-Issuer is already aware
    of the progress of the requested operation, such as when the
    REFER-Issuer has an explicit subscription to the dialog event package
    at the REFER-Recipient, the implicit subscription and resultant
    NOTIFY traffic related to the REFER can create an unnecessary network
    overhead.























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4.  Definition

    This document defines a new option tag, "norefersub", which specifies
    that an implicit subscription for event package refer should not be
    created as a result of accepting this REFER request.

    The "norefersub" option tag MUST be used by the REFER-Issuer only
    when the REFER-Issuer can be certain that the REFER request will not
    be forked.

    The REFER-Issuer can place the "norefersub" option tag either in the
    Require header or in the Supported header of the REFER request,
    subject to application requirements.

    If the REFER-Issuer inserts the option tag in the Supported header
    but the REFER-Recipient doesn't grant the suggestion, an implicit
    subscription is created as in default case.

    If the REFER-Issuer inserts the option tag in the Require header but
    the REFER-Recipient is not willing to grant the request, the REFER
    request is rejected.

    If the REFER-Recipient is willing to grant the "norefersub" behavior
    for the issued REFER request, it MUST insert a Supported: norefersub
    header in the 2xx response to the REFER-Issuer.  In this case no
    dialog is created.

























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5.  Preventing Forking of REFER Requests

    The REFER specification allows for the possibility of forking a REFER
    request which is sent outside of an existing dialog.  The
    REFER-Issuer can ensure that REFER doesn't get forked by sending
    REFER to a REFER-Recipient which has GRUU properties according to
    definitions of [5].












































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6.  Example

    An example of REFER which suppresses the implicit subscription is
    shown below:

    REFER sip:pc-b@tradewind.com SIP/2.0
    Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1
    From: <sip:a@tradewind.com>;tag=1a
    To: <sip:pc-b@tradewind.com>
    Call-ID: 1@issuer.tradewind.com
    CSeq: 234234 REFER
    Max-Forwards: 70
    Refer-To: <sip:c@tradewind.com;method=INVITE>
    Require: norefersub
    Accept-Contact: *;audio;require
    Contact: sip:a@issuer.tradewind.com
    Content-Type: message/sipfrag
    Content-Id: <1239103912039@issuer.tradewind.com>
    Content-Length: ...
































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7.  IANA Considerations

    This document defines a new option tag, "norefersub", which specifies
    that no implicit subscription should be created as a result of
    accepting the REFER request.  This option tag is only meaningful for
    the REFER request defined in RFC3515.













































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8.  Security Considerations

    This extension doesn't introduce new security threads beyond those
    identified and addressed in the core SIP specifications.















































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9.  Acknowledgements

    The SIP community would like to thank Sriram Parameswar for his ideas
    being originally presented in draft-parameswar-sipping-norefersub-00
    and incorporated in this document.














































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10.  References

10.1  Normative References

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

    [2]  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.

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

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

10.2  Informational References

    [5]  Rosenberg, J., "Obtaining and Using Globally Routable User Agent
         (UA) URIs (GRUU) in the  Session Initiation Protocol (SIP)",
         draft-ietf-sip-gruu-02 (work in progress), July 2004.


Author's Address

    Orit Levin
    Microsoft Corporation
    One Microsoft Way
    Redmond, WA  98052
    USA

    Phone: +1-425-722-2225
    EMail: oritl@microsoft.com

















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Acknowledgment

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    Internet Society.




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