Imagine a call from a SIP user to the PSTN via a B2BUA.
The call may first be sent from the B2BUA to the PSTN gateway, and a
183 w/SDP sent back to the UAC, where the SDP has connection info for
the PSTN gateway. If the call doesn't succeed after a few rings, then
the B2BUA may CANCEL the call to the PSTN gateway and INVITE a media
server; if it accepts with a 200 OK, then the B2BUA would return the
media server's SDP to the UAC.
UAC B2BUA PSTN GW MS
| | | |
|--INVITE--->| | |
|<--100------| | |
| |---INVITE------>| |
| |<--100----------| |
| |<-183 w/SDP-----| |
A|<-183 w/SDP-| | |
| |--CANCEL------->| |
| |-------------------INVITE-------->|
| |<------------------200 w/SDP------|
B|<-200 w/SDP-| | |
| | | |
So the SDP of "A" != the SDP of "B".
However RFC 3264 on the Offer/Answer model says:
At any time, either agent MAY generate a new offer that updates the
session. However, it MUST NOT generate a new offer if it has
received an offer which it has not yet answered or rejected.
Furthermore, it MUST NOT generate a new offer if it has generated a
prior offer for which it has not yet received an answer or a
rejection.
This doesn't seem to preclude "modifying the answer"; is anyone aware
of a rule against this?
Mark R. Lindsey | ECG | +1-229-316-0013 | [EMAIL PROTECTED] |
On Apr 20, 2007, at 10:12 AM, Siva M-Q16748 wrote:
>
> Can the SDP of 183 and 200 OK be different
>
> I read somewhere that they should be the same
>
> If so , Is there any Logical reason why these two should be
> different ??
>
> Siva M
>
>
> Siva M
>
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