Subject: RE: [Sip] interwork timer in RFC 3398

From: Adam Roach <[email-masked]>
Date: Mon, 13 Oct 2003 09:29:18 -0500

> In section 7.1.6 from RFC 3398 (ISUP to SIP mapping), the call flow
> talks about interwork timer. Does this timer correspond to a standard
> ITU timer (like T9, T7, etc ...) ?

No. This timer is necessary to ensure that the ISUP circuit is
freed, even if the SIP endpoint dies. Its value is up to the
implementor; I would allow long enough for the announcement
to be played several times -- probably on the order of 1 minute.

> When should it exactly be started ? Right after IAM sent or
> after ACM received ?

That's really an implementation choice; however, since it's
not necessary unless an ACM is received with a cause code
in it, I would wait for the ACM.

> Another question about the same call flow :
> Why does the MGC have to send SDP in his 183, while SDP
> contained in the initial INVITE is sufficient to establish
> early media in backward direction ?

You're right; it's not strictly necessary in this case. For
most of the early media cases in this document, there was
a potential need for forward media (e.g. to send DTMF to an
IVR system), and this use case was copied largely from those.

/a

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---

From: Natesan Kannan <[email-masked]>
Date: Thu, 16 Oct 2003 14:22:16 +0530

On a totally different subject wrt to RFC 3398, the state machine in section
7.2 has wrong section numbers for event descriptions, probably copied from
the earlier draft.
Sorry if it has already been taken care of...
-Kannan
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