Anand Vasudevan wrote:
>
> Hi,
>
> bis-03 section 17.1 (Redirect server) says "After receiving a request
> other than CANCEL, the server gathers the list of alternative locations
> and returns a final response of class 3xx or it refuses the request. The
> redirect server maintains transaction state for the whole SIP
> transaction."
>
> a) Does it mean that Redirect returns 3xx for ACK request also? However,
> this contradicts the basic rule "ACK doesn't generate any response"
No; ACKs are not responded to.
> b) Redirect can receive ACK in two ways - acknowledgement of 3xx for
> INVITE and erroneous ACK. Since redirect is transaction-based, how does it
> discriminate between those two ACKs.
In case of an ACK for a 3xx response, the Redirect server can match the ACK
to the transactions it is handling (CSeq will be the same as the INVITE,
the Redirect server will have added a tag in the To of the 3xx response
which will be echo'ed in the ACK, etc.), and stop retx'ing the 3xx response.
In case of receiving an erroneous ACK, the Redirect server will soon find
out that it does not match any of its transactions. It can silently discard
it.
Regards,
- vijay
--
Vijay K. Gurbani vkg@{lucent.com,research.bell-labs.com,acm.org}
Internet Software and eServices Group
Lucent Technologies/Bell Labs Innovations 263 Shuman Blvd., Rm 1A-413
Naperville, Illinois 60566 Voice: +1 630 224 0216 Fax: +1 630 713 0184
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