Hello,
In the SIP specification is written :
" The ACK request is forwarded as the corresponding INVITE request, based
on its Request-URI and thus MAY take a different path than the
original INVITE request,.. "
and
"The ACK request does not generate responses for any transport protocol."
Assume that the ACK is not sent directly from a user agent client to a user agent
server,
but sent to a Proxy and the Record header is not present. In this case the ACK is
processed
in the same way as the original INVITE.
Assume that the proxy contacted a Redirect Server for the INVITE, it may contact the
Redirect Server
for the ACK too. If the Redirect follows the rules (see above), it does not generate a
response.
The ACK will never reach the user agent server and the call setup will not be
successfull.
Regarding this problem there arise several questions :
(1) Is this a realistic scenario in existing networks ?
(2) MUST the client send the ACK directly to the user agent server, if it is not
willing (ignore the
Record-Route header) or no able (Record-Route header is not present in the 200
OK)
to insert the Route header into the ACK ?
(3) Is it acceptable, that the call setup is terminated, if the user agent client does
not follow the rules of (2) ?
(4) What is the real behavior of a Redirect Server ?
Shouldn't the Redirect Server proxy the ACK, if it is not destined for itself ?
Or should it answer the ACK, because the Redirect Server is considered to be a
database
the Proxy Server can use for look up ?
(5) Should the Proxy provide any additional function to handle the problem ?
Should the Proxy discard ACK without Record header, instead of forwarding it ?
Thanks,
Elke Neum�rker
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