Subject: [Sip] greener question for "contact" header field

From: Lei Liang <[email-masked]>
Date: Thu, 4 Oct 2001 12:28:00 +0100 (BST)

hello, everyone,
 I see the "contact" header is used to specify the sender's addr. does the
caller and callee always use this addr to communicate after they get
it? looks it's more efficient to use the addr in "contact" header but not
the one in "To" as the destination addr, doesn't it? 
another question is the RFC said using the "contact" addr can avoid the
proxies. but it's impossible for me because it has to pass firewall, a
kind of proxy, if the caller or callee is behind it. am I right?
thanks a lot for ur reading.
cheers.
lei 

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