Hi,
Taking up the same scenarios where I the UAC had sent an INVITE to my
proxy & it forked it further.
Now, the UAC gets 18Xs from multiple locations, with the only difference
being the tag in the "To" header.
Assuming the UAC further gets a 200 & wants to CANCEL the other 18X it
got, where should it send the CANCEL to? THE UAC is using UDP & there
was no contact in the 18x received. Is the UAC expected to store the IP
address from which it got the 18X & reuse the same while sending CANCEL.
I don't think that is the intent.
Section 5.2 of bis 03.txt says " ...The Request-URI, topmost Via,
Call-ID, To, the numeric part of CSeq
and From header fields in the CANCEL request are identical to those
in the original request being cancelled, including tags. This allows
a CANCEL request to be matched with the request it cancels"
If that is the case then how will the CANCEL be related to the 2nd call
leg, because the CANCEL does not have the to tag of the 18x response but
instead it has the whole to header from the original request.
Another thing Section 5.2 of bis 03.txt also says that
"A proxy client generates a CANCEL request for branches without
a final response after it has forked a request and receives a 2xx or
6xx response from one of the branches. "
Whereas section 17.4, pg. 122 says that
"After receiving a 2xx, the server MAY terminate all other
pending requests by sending a CANCEL request"
Note that there is no "MAY" in section 5.2.
I have a basic question here. The intent of the UAC by sending the
INVITE to the proxy was to open just one call leg, but the proxy's
forking resulted in formation of multiple call legs. Now why isn't it
made mandatory in SIP for the proxy to handle all these extra multiple
call legs & present the UAC with just one 2xx for one call leg only. Why
is it left as a "MAY" for the proxy to CANCEL the multiple pending call
legs. As I said earlier the intent of the UAC is to get to the UAS at
just one location, why should the UAC be troubled with the multiple 2XXs
from multiple locations.
The proxy has the all the information regarding who all it had forked
the INVITE to, & in my opinion the proxy is the best entity to CANCEL OR
BYE the extra call legs, then why has it been left to the UAC to handle
multiple 2XXs by using the word "MAY" above.
--
Regards,
Harpreet Ahluwalia
Lucent Technologies
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