[SIPForum-discussion] Header Replaces and Parameter Replaces

[Thomas_Young at 3com.com]

Hi Doug and all,

  Please disregard my previous message, I finally find that RFC3515 refers 
to RFC5589 which refers to RFC3891. 

Thanks and best regards!

 Thomas Young
 



Thomas Young/C/US/3Com
2010-01-28 10:47

To
Doug Sauder <doug.sauder at dsauder.com>
cc
discussion at sipforum.org
Subject
Re: [SIPForum-discussion]  Header Replaces and Parameter Replaces





Hi Doug,

  Thank you for helping me understand the Replaces parameter in Refer-to 
header is one of headers field in the SIP URI.

  But again, where does the Replaces come from without "introduction", we 
know Replaces header is specified in RFC3891, however RFC 3515 did not 
refer to RFC3891. If it did, that makes sense. 


Best regards!
 Thomas Young
  




Doug Sauder <doug.sauder at dsauder.com> 
2010-01-27 17:02

To
Thomas Young/C/US/3Com at 3Com
cc
discussion at sipforum.org
Subject
Re: [SIPForum-discussion]  Header Replaces and Parameter Replaces






The Replaces "parameter" here is a header field in the URI.  See section 
19.1.1 in RFC 3261.

--
Doug

Thomas_Young at 3com.com wrote: 

Hi All, 

    RFC 3515 defines a Refer method and Refer-to header, and gives us an 
example of Refer-to header with Replaces parameter below: 
      Refer-To: <sip:dave at denver.example.org
?Replaces=12345%40192.168.118.3%3Bto-tag%3D12345%3Bfrom-tag%3D5FFE-3994>

Unfortunately, I can't see any formal description about this Replaces 
parameter this spec. 
    

  
    RFC3891 defines the Replaces header with following syntax/format: 
       Replaces = "Replaces" HCOLON callid *(SEMI replaces-param)
      replaces-param = to-tag / from-tag / early-flag / generic-param
      to-tag = "to-tag" EQUAL token
      from-tag = "from-tag" EQUAL token
      early-flag = "early-only" 

    Examples:
      Replaces: 98732 at sip.example.com ;from-tag=r33th4x0r ;to-tag=ff87ff
      Replaces: 12adf2f34456gs5;to-tag=12345;from-tag=54321;early-only
      Replaces: 87134 at 171.161.34.23;to-tag=24796;from-tag=0 

Please notice: this Replaces header has little bit different format from 
tha above Replace parameter which has some unfixed separators like ?, 
 %3B,%D. 
  

   Also RFC3891specifies that Replaces header can be only used in Invite 
method as below: 
The Replaces header field indicates that a single dialog identified by the 
header field is to be shut down and logically replaced by the incoming 
INVITE in which it is contained. It is a request header  only, and defined 
only for INVITE requests......

      Header field    where   proxy   ACK  BYE  CAN  INV  OPT  REG  MSG
     ------------    -----   -----   ---  ---  ---  ---  ---  ---  ---
     Replaces          R              -    -    -    o    -    -    -


                                     SUB  NOT  REF  INF  UPD  PRA  PUB
                                     ---  ---  ---  ---  ---  ---  ---
     Replaces          R              -    -    -    -    -    -    -




 Here I'm just wondering why RFC3515 just gives an example of Replaces 
parameter in the Refer-to header without any formal description about its 
syntax or format(how to parse the unfixed separators), even I know 
RFC5359(SIP Service Examples) and RFC5589(SIP Call Control-Transfer)tell 
us how to use it. 


Thanks and best regards
 Thomas Young
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