Subject: [Sip] Bis-05: C timer issue

From: Christer Holmberg <[email-masked]>
Date: Thu, 01 Nov 2001 11:26:34 +0200

Hi,

I brought this up in the INVITE-1xx-CANCEL thread, but since it is a
separate issue I will bring it up separately.

In bis-05, chapter 17.1.1.2 says:

If the client transaction receives a provisional response while in
the "calling" state, it transitions to the "proceeding" state. Upon
entering this state, the client transaction MUST start timer C with
the value provided by the TU when the client transaction was created.
This timeout dictates how long the client transaction waits for a
final response before giving up (i.e., roughly how long does it "let
the phone ring"). In the "proceeding" state, the client transaction
SHOULD NOT retransmit the request any longer. Furthermore, the
provisional response MUST be passed to the TU. Any further
provisional responses MUST be passed up to the TU while in the
"proceeding" state. When timer C fires, the client transaction MUST
transition to the terminated state, and it MUST inform the TU of the
timeout.

My questions are:

1. Does a new provisional response reset the C timer? The state machine
on page 95 shows that the client does remain in the "proceeding" state,
but it doesn't say anything about reseting the C timer.

The next question is valid only if the answer to the first question was
'yes' :)

2. If the client receives provisional responses from multiple servers,
does it have a C timer for each leg? For example, UAS 1 may send many
provisional responses, so C doesn't expire, but UAS 2 sends only one
provisional response, and then nothing else before the C timer expires.
Now, in this case, should the client should terminate (send BYE) for
that specific leg? OR, does the client only have a single C timer for
the whole call, and doesn't (from the C timer point of view) care where
the provisional responses come from?

3. First, I know that transactions are "handled separately". But, if the
client does not receive futher responses (provisional or final) before
the C timer expires, but it DOES receive something else related to the
call (COMET, PRACK responses, INFO responses etc etc), should it still
terminate the call setup?

Regards,

Christer Holmberg
Ericsson Finland

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---

From: Gonzalo Camarillo <[email-masked]>
Date: Thu, 01 Nov 2001 22:34:41 +0200

Hello Xter,

No, timer C is not reseted when more provisional responses arrive. The
spec says that it is "roughly" how long the phone rings because it is
usually started by a 100 Trying response rather than a 180 Ringing
response.

Regards,

Gonzalo

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