HI Shinji,
I noticed the chart in your mail showed ,SDP4 and SDP5 both exist in reliable response(1xx-rel). In my mind, no matter SDP5 is offer or answer, it shouldn't be allowed.
UAC UAS
| F1 INVITE (SDP1) | <-- offer
|-------------------->|
| F2 1xx (SDP2) |
|<--------------------|
| F3 1xx (SDP3) |
|<--------------------|
| F4 1xx-rel (SDP4) | <-- answer
|<--------------------|
| F5 1xx-rel (SDP5) |
|<--------------------|
| F6 1xxl (SDP6) |
|<--------------------|
| F7 2xx INV(SDP7) |
|<--------------------|
| F8 ACK |
|-------------------->|
(PRACK transactions are not shown)
Shinji: Just you said "different SDPs(compare with the answer) can
exist in non-reliable response and final 2xx response".
Eric: I mean different SDPs may appear in non-reliable response,because some SERVER may use 1xx with SDP
to play some announcements before foward a call, eg a charge server "HI guy, you have only 5 minute to communicate",
or, a redirect server "the call is forwarding"! If the server want to use reliable response, it must use re-INVITE after
the call is established ,for the SERVER cannot send the SDP in final response from UE-B to UE-A.But if the SERVER
use non-reliable response, the SERVER may use final response to carry SDP.
UE-A SERVER UE-B
| - INVITE -> | |
| <-18x-------- | |
| | -INVITE ->|
| | |
BR
Eric
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