Harpreet Ahluwalia wrote:
>
> Hi,
>
> Refering to bis03:
>
> The definition of a transaction is
> "... all messages from the first request
> sent from the client to the server up to a final (non-1xx)
> response sent from the server to the client. A transaction
> is identified by the CSeq sequence number (Section 10.20)
> within a single call leg ..."
>
> Consider the scenario that I am a UAC, I send an INVITE to my outbound
> proxy. The proxy forks it to n other servers.
> Now, I could end up getting n 18Xs ( or even n 200 ) responses. All
> these will have the same Cseq no. So, do all these 18Xs & 200s form a
> part of the same transaction? Going by definition the transaction
> should end the moment it gets the first 200. Which means the other 200s
> belong to a NULL ( already deleted) transaction!
Not quite. UAs, besides being aware of a transaction, are also aware of
call-legs. A call leg is not established until a 200 OK is received (this
is somewhat debatable since 100rel may force an "early" call leg). So, even
if you get multiple 1xx (each with a different tag in the To), they update
the same INVITE transaction. When you get the first 200 OK, a call leg is
established. Successive 200 OK establish further call legs based on the
original INVITE transaction.
> Also, I as the UAC don't know how many people the proxy had forked the
> request to. So, for how long should I maintain the state of the
> transaction, I could get n 180s for that transaction. I don't know
> whether the 200s belong to the same transaction or not.
I don't know off hand if the bis specifies a caching period for a UAC where
they have to maintain the INVITE transaction after sending an ACK to the
first 200 OK it receives. If it does not, 32s seems an appropriate time to
maintain the transaction. By that time, all straggler 200 OKs should have
arrived.
- 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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