Note first that ACK (the acknowlegement) applies only to INVITE. An ACK to a non-2xx final response will follow exactly the path the request took. Study the way proxies treat non-2xx final responses. The receiving UA will have received its ACK from its previous hop proxy. You need to send yours the same place the INVITE went. If you are able to tell which UA sent the final response (in most cases you won't be able to), sending the ACK directly to it would be a waste of effort on your part (it would be ignored) and it will leave the state machines at the intermediaries in a non-terminal state (possibly retransmitting) for an unnecessary period of time.
An ACK to a 2xx final response will follow whatever route set the 2xx established. You have a URI (not necessarily an IP address) for the far UA at this point, but you may not be able to resolve that URI to anything meaningful and even if you can, you may not be able to send SIP packets directly to it. The ACK MUST traverse the intermediaries that requested to stay on the path of future requests (they added Record-Route, which establishes the route set). RjS On Wed, 2002-03-27 at 21:31, alok khemka wrote: > in sip when there are proxie server/s involved in forwarding the invite > message the acknowledge traverses the same path the invite came from. what > are the pitfalls of sending the acknowledgment directly to the caller??? > (callee know the ip address of the caller by now!!!) > > Alok Khemka > Graduate Student > Computer Science Dept. > mail: [EMAIL PROTECTED] > [EMAIL PROTECTED] > [EMAIL PROTECTED] > cell: 816-352-6824 > > > _________________________________________________________________ > Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp. > > _______________________________________________ > Sip-implementors mailing list > [EMAIL PROTECTED] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
