Attila Sipos wrote:
I have a user-agent which gets an INVITE (sent over TCP)
from some kind of server.
OK, so it is a UAS for that transaction ...
The user-agent keeps this TCP socket open for the
duration of the call. At the end of the call, the
user-agent user hangs up and so the user-agent sends
a BYE using the same original TCP connection.
So, the UAS now becomes a UAC to send a BYE ... so far okay ...
This is OK isn't it?
The server does not see the BYE.
So here is where it gets interesting. Consider the well known
and immensely loved SIP trapezoid:
P1 ----------> P2
/\ /\
/ \
/ \
/ \
UE A UE B
where UE {A,B} are end points and P{1,2} are intermediaries
(proxies).
Assume all communications are over TCP, and also suppose
that P1 R-Rs, but P2 does not. The INVITE comes from
UE A and the subsequent BYE from UE B. During the INVITE, P1 R-R'd,
P2 did NOT.
When UE B sends a BYE, there is no point in sending it to
P2, an open TCP connection notwithstanding (UNLESS, of course,
P2 is the default outbound proxy for UE B's domain). If P2 is
not the default outbound proxy, then UE B should open
a new TCP connection to P1 to send the BYE (since P1 R-R'd).
The server makers complain that the user-agent
should drop the original TCP and open up a new
one to send the BYE.
Is this really necessary?
Generally speaking, if an end point is configured with a
default outbound proxy, there isn't any need to open
up a new TCP connection. The old one can be re-used.
Chris Boulton has pointed you to some of the work we have
done in establishing TCP guidelines (at
http://www.ietf.org/internet-drafts/draft-gurbani-sipping-
connection-guidelines-01.txt -- mind the line break). We
will be rev'ing this I-D over the next couple of weeks
to make a bit more streamlined. But it should provide some
usable guidelines, even in its current form. All feedback
is, of course, welcomed.
Thanks,
- vijay
--
Vijay K. Gurbani, Ph.D. [EMAIL PROTECTED],research.bell-labs.com,acm.org}
Wireless Networks Group/Internet Software and Services
Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
Naperville, Illinois 60566 Voice: +1 630 224 0216
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