Subject: [Sipping] I-D ACTION:draft-ietf-sipping-isup-00.txt (WGLC reminder)

From: [email-masked]
Date: Thu, 29 Nov 2001 18:03:52 -0500

Hi,

I have few early media related questions on the Sipping-isup document as
follows.

(1) In the SIP to ISUP flow in Section 6.1.1, at Step 3, when the PSTN is
sending audio stream and the MGC/MG allows it, will the UAC play media to
the caller without receiving the 18x containing remote SDP? What is the
expected behaviour of the UAC in this case?

(2) In the same flow at Step 4, when the UAC receives a 18x containing
remote SDP, the early media path in the IP network is practically cut
through in both directions because nothing will stop the UAC from sending
media. Is this right?

(3) In Section 6.2.6, ACM received, there is a paragraph stating, "Usually
on receipt of an ACM, a `180 Ringing' is sent to the SIP network.  It
should generally contain a session description in order to allow SIP UAs to
prevent clipping of initial callee media." Also in Section 7.2.3, 18x
received, there is a paragraph stating, "If the reception of a `180
Ringing' response without media description, the MG generates the ringback
tone to be heard by the caller."

Does the above mean the following for an ISUP to SIP flow?
-- If 180 Ringing without SDP is received, the MGC/MG should generate local
ringback tone towards the PSTN caller.
-- If 180 Ringing with SDP is received, the MGC/MG should NOT generate
local ringback tone but relay media received from SIP UAS to the PSTN.

Thanks,
YoungSun

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