I am just beginning to implement SIP and am having some trouble understanding the use of the port number in the VIA header Please consider the following two scenarios:
1. Point-to-point SIP call, that does not go through a proxy: Consider the case where my machine has multiple adapter and I can send and receive messages on either one. However, I opt to do a listen on only one of the adapters at a the default port. adapter A x.x.x.1 - listens on port 5060 adapter B x.x.x.2 - does not listen Now if a sip call is placed, I would encode the VIA field to contain the IP address of the adapter that I want the message to be received on. However, if the message actually gets sent on the other adapter.Now the VIA header in the INVITE is INVITE .. VIA: x.x.x.1 The receiver adds the actual IP that the message was received from. The VIA headers on the callee would look like this VIA: x.x.x.1, received:x.x.x.2 So now the response is going to get sent to a IP address and port combo, that I am not listening on. My question is, how does SIP support a multiple adapter scenario such as this, using the UDP as the transport? In this case, if the response was just automatically sent to the IP and port that the request came from, it would work. But the VIA header seems to add a level of confusion. 2. SIP call thru a proxy: If the caller is listening on a port other than the default port, the port info is added to the VIA header. Caller sends INVITE with VIA header VIA: x.x.x.1: 5062 The proxy adds it own address to the VIA and send it to the Callee VIA: y.y.y.y VIA: x.x.x.x:5062 Now does the caller send the response to y.y.y.y:5062 or does he send it to y.y.y.y and the default port? If the port sent to is 5062, and the proxy is not listening on that port, we are again broken! Does this imply that the proxy should start listening on all non-default ports that the callers use, in order to work?? My interpretation of the protocol may be wrong. I would appreciate some clarification on these issues. Thanks Mitu Aggarwal _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
