Internet DRAFT - draft-abhishek-refer-to-event-parameter


Network Working Group                                      Abhishek Gupta
Internet-Draft                                     Independent Consultant          
Intended status: Standards Track                            June 20, 2015
Expires: Dec 19, 2015                                         

 Conveying Event Tag with the Session Initiation Protocol REFER Method

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   This document extends the REFER method, defined in RFC 3515, to
   convey feature parameters defined in RFC 3840.


   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [1].
   To simplify discussions of the REFER method and its extensions, three
   new terms are used throughout the document:

    - REFER-Issuer: the UA issuing the REFER request
    - REFER-Recipient: the UA receiving the REFER request
    - REFER-Target: the UA designated in the Refer-To URI


   This document extends the SIP REFER method defined in RFC 3515
   to be used with feature parameters defined in RFC 3840.

   Feature tags are used by a UA to convey to another UA information
   about capabilities and features. This information can be shared by a
   UA using a number of mechanisms, including OPTIONS responses. 

   Feature tag information can be very useful to another UA. It is
   especially useful prior to the establishment of a subscription, 
   triggered only through REFER method. This is valid only for the request
   containing parameter "method=SUBSCRIBE" in Refer-To header. While 
   sending this request if there is no mechanism to indicate as to which 
   event is to be subscribed, the REFER-Recipient may send SUBSCRIBE with 
   an undesired event. For example, if a REFER-Issuer knows (through an 
   OPTIONS query, for example) that the remote REFER-Target supports 
   events like dialog the REFER-Recipient might subscribe with dialog 
   or any other event as specified.

   This extension to the REFER method provides a mechanism by which the
   REFER-Issuer can provide this useful information about the REFER-Target
   capabilities and functionality to the REFER-Recipient by
   including feature tags in the Refer-To header field in a REFER


   1.   The example below shows how the REFER-Issuer tells the REFER- 
        Recipient that the REFER-Target supports dialog event package.  

        Refer-To: <;method=SUBSCRIBE>;events=dialog

   2.   In case the REFER-Recipient doesn't support the desired event in 
        the Refer-To header, a 489 Bad Event will be responded to REFER 

Security Considerations

   Feature tags can provide sensitive information about a user or a UA.
   As such, RFC 3840 cautions against providing sensitive information to
   another party.  Once this information is given out, any use may be
   made of it, including relaying to a third party as in this

   A REFER-Issuer MUST NOT create or guess event tags - instead an
   event tag included in a REFER SHOULD have been discovered in an
   authenticated and secure method (such as an OPTIONS response) 
   directly from the REFER-Target.

   It is RECOMMENDED that the REFER-Issuer includes in the Refer-To
   header field the desired feature tag that were listed in the most 
   recent Allow-Events header of the REFER-Target.


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]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User
        Agent Capabilities in the Session Initiation Protocol (SIP)",
        RFC 3840, August 2004.

Authors' Addresses

   Abhishek Gupta
   Independent Consultant
   Navi Mumbai - 400701
   Mobile: +91-9930230341