SIP FAQ : SIP Protocol Operation : Can a proxy fork a non-INVITE request? If yes, what happens if it gets multiple responses?
	Yes, a proxy can fork a non-INVITE request. However, it must forward only a single response upstream, 200 or otherwise. Thus, only a single 200 is ever forwarded upstream. This is in contrast to INVITE, where all 200's received are forwarded upstream. Why is that? The reliability mechanism of non-INVITE requests dictates that. Response retransmissions are triggered on request retransmissions. Thus, the client retransmits its request until it gets *a* response. So, upon receiving the first final response, the client would cease retransmitting the request, and then there would be no way to reliably send the other final responses. As a result of this, forking of non-INVITE requests is only useful when the method has semantics that meet certain criteria. Specifically, (1) the client doesn't care which server gets the request, (2) the client doesn't care which server sent the response, or even if multiple servers sent a response, (3) the service provided by each server is identical. In essence, forking of non-INVITE requests is useful only for an anycast type of service.
	[Append to This Answer]
	jdrosen@dynamicsoft.com
	2000-Nov-19 5:18pm

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