Hello Vikram,
If you take a look at the bis05, at several places you will find mention
that a 2xx response to an INVITE is treated differently than other
responses, this is since a 2xx is handled end to end. It is retransmitted
ONLY by a UAS and accepted only by a UAC. A proxy that comes in between
should neither eat up any 2xx's nor retransmit any 2xx. This means that the
server transaction should not do the job of waiting for the ACK or of
retransmitting 2xx, since that is done by the TU.
This is why any 2xx that the server transaction receives need to be passed
to the transport layer for transmission, and the transaction itself must
move to the terminated state. As regards waiting for an ACK this is done by
the TU itself . I copy this text from bis05 13.3.1.4 that deals with callee
handling of Invite Requests.
"Once the response has been constructed it is passed to the INVITE server
transaction. Note, however,
that the INVITE server transaction does not retransmit 2xx responses to an
INVITE. Therefore, it is neces-
sary to pass periodically the response to the server transaction until the
ACK arrives. The 2xx response is
resubmitted to the server transaction with an interval that starts at T1
seconds and doubles for each retrans-
mission until it reaches T2 seconds (T1 and T2 are defined in Section 17).
Response retransmissions cease
when an ACK request is received with the same dialog ID as the response.
This is independent of whatever
transport protocols are used to send the response."
-Regards
R.Kamath
Vikram Varma <[EMAIL PROTECTED]> on 11/20/2001 02:24:55 PM
To: "'[EMAIL PROTECTED]'"
<[EMAIL PROTECTED]>
cc: (bcc: P Raghavendra Kamath/HSSBLR)
Subject: [Sip-implementors] bis 05 state machines
A while ago there was a question about Figure 7 on page 74, the INVITE
server transaction state machine. I am not sure I understand the diagram.
If a 200 response is received in the proceeding state, then shouldnt the
transaction move to the completed state, waiting for an ACK?
If not, and the ACK is considered a new transaction, Figure 8 no longer
applies.
Could someone clarify this?
Thanks,
Vikram
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