RE: [Sip] regarding session modification

What is the header field that is changed in all re-INVITEs.
What is the value of this header field in each scenario?

________________________________

From: Srinivas [mailto:srinivasj@huawei.com]
Sent: Wed 1/16/2008 7:00 PM
To: sip@ietf.org
Subject: [Sip] regarding session modification

Hi all,

Consider the following scenarios. 

1. 

C->S: INVITE (for speechrecog)

S->C: 200 OK

C->S: ACK

Now the SIP session is established b/w UAC and UAS. speechrecog resource is active on the established sip session

C->S: INVITE (re-INVITE for adding speechsynth resource)

S->C: 200 OK 

Offer/Answer fail for the new resource, TTS (speechsynth).

2. 

C->S: INVITE (for speechrecog)

S->C: 200 OK

C->S: ACK

Now the SIP session is established b/w UAC and UAS. speechrecog resource is active on the established sip session.

C->S: INVITE (re-INVITE for adding speechsynth resource)

S->C: 200 OK 

Offer/Answer fail for the for the existing ASR(speechrecog) resource also.

3.

C->S: INVITE (for speechrecog)

S->C: 200 OK

C->S: ACK

Now the SIP session is established b/w UAC and UAS. speechrecog resource is active

C->S: INVITE (re-INVITE for adding speechsynth resource)

S->C: 200 OK

C->S: ACK

Now both speechrecog and speechsynth are active on the sip session

C->S: INVITE (re-INVITE for removing speechsynth resource)

S->C: 486 BUSY HERE

What should be the behaviour of UAC in the above scenarios?

Regds,

Srinivas