[SIPForum-discussion] Handling modified re-transmission responses

[Vishu]

Hi All,

I have been trying to inteop with a server for a simple voice call setup,
but stuck with a scenario explained below.
The server is responding back with a unreliable provisional resposne
initialy (first response) but its subsequent responses are all reliable
provisional response with Supported header with 100rel.

According to the section 17.1.3 in RFC 3261, our client does teats this (2nd
response) response as re-transmitted resposne and ignore.
Is the server right in doing by adding/deleting header from the earlier sent
response? If its wrong, what is the alternate to be done?
If its correct, then the client should always process every re-transmitted
response.  Please suggest


*UA-1-> UA-2 *

   INVITE sip:bob at biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: Alice <sip:alice at atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob at biloxi.example.com>
   Call-ID: 3848276298220188511 at atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice at client.atlanta.example.com;transport=udp>
*   Supported: 100rel*
   Content-Type: application/sdp
   Content-Length: 151
   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

*UA 1 <--- UA2*
 SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice at atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob at biloxi.example.com>
   Call-ID: 3848276298220188511 at atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0

* UA 1 <--- UA2 (First response with P-Early-Media)*
SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice at atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob at biloxi.example.com>;tag=8321234356
   Call-ID: 3848276298220188511 at atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob at client.biloxi.example.com;transport=udp>
 *  P-Early-Media: inactive*
   Content-Length: 0


* **UA 1 <--- UA2 (Second resposne with P-Early-Media header removed
and Require header added!!)
*
  SIP/2.0 180 Ringing
  Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice at atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob at biloxi.example.com>;tag=8321234356
   Call-ID: 3848276298220188511 at atlanta.example.com
   CSeq: 1 INVITE
*   Require: 100rel*
   Contact: <sip:bob at client.biloxi.example.com;transport=udp>
   Content-Length: 0
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