From: "Sweeney, Andrew \(Andrew\)" <[EMAIL PROTECTED]> Why is "Fake Forking" OK to do?
Because the UAC cannot distinguish it from the situation where two UASs have received forks of the INVITE and each UAS is establishing a separate early dialog with the UAC. What is the issue that the SDP can only be changed during "Fake Forking" and if this is acceptable then it seems that changing streams between 18x and 200 should be OK as well. The short answer is "RFC 3261 (or some such) forbids it." The long answer is that because the network may reorder messages, if there is different SDP for different responses within a single transaction, the UAC cannot reliably determine which SDP is the "most recent" SDP. (SDP from responses on different forks have different to-tags, and so can be properly classified. SDP from responses in different transactions can be ordered by their CSeq numbers.) The more subtle answer is that it is not possible in general to determine which early dialog SDP is the "right one" to render, and the UAC is likely to have to use some careful hueristics to provide a good user experience. (Which is one reason why Christer's (?) 190 response would be a good idea -- once a UAC receives a 190 for a branch, it knows that that branch's SDP can be safely ignored.) Dale _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
