Subject: [Sipping] forking for ISUP to SIP call

From: [email-masked]
Date: Wed, 6 Feb 2002 11:59:17 -0500

Hi,

I have a question on forking for an ISUP originated call that is
terminating to a SIP device.
Suppose the following scenario.

PSTN ---- IAM----> SIP-GW ----- INVITE -----> SIP network
PSTN <----ACM---- SIP-GW <----- 180----- SIP-device-1
PSTN <----???---- SIP-GW <----- 183----- SIP-device-2
PSTN <----???---- SIP-GW <----- 180----- SIP-device-3

How are the multiple 18xs for different call legs mapped to ISUP?

Thanks,
YoungSun

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From: Michael Hammer <[email-masked]>
Date: Wed, 06 Feb 2002 13:24:47 -0500

YoungSun,

As the SIP network introduced the forking, shouldn't it resolve the forking 
on behalf of the PSTN caller?  The SIP side of the SIP GW is the client 
that initiated the SIP call.  That agent should resolve the issue and not 
pass it on to the PSTN.  This is not any different than if a switch in the 
PSTN had invoked a service such as sequential or parallel hunt groups.

Mike

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From: Christer Holmberg <[email-masked]>
Date: Thu, 07 Feb 2002 07:34:27 +0200

Hi Michael,

The proxy which "introduced" the forking WILL forward ALL PROVISIONAL
responses to the SIP GW, but it should only forward ONE final response.

Regards,

Christer Holmberg
Ericsson Finland

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From: Michael Hammer <[email-masked]>
Date: Thu, 07 Feb 2002 10:17:17 -0500

Yes, of course.  It was not clear where the forking was occurring in the 
given scenario, and I did not clarify that point.  Thanks.

Mike

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 07 Feb 2002 10:55:25 -0500

> >responses to the SIP GW, but it should only forward ONE final response.

Thats not true. It may end up forwarding multiple 2xx responses if the
CANCEL and 2xx pass on the wire.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
Chief Scientist                         First Floor
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From: Michael Hammer <[email-masked]>
Date: Fri, 08 Feb 2002 10:34:02 -0500

Jonathan,

Let's not get off on a tangent.  Let's just say that all normal SIP 
processing occurs as defined by your draft.  Christer was noting where the 
forking occurs might be at the PSTN GW as well as in the SIP network.  My 
point was that the nuances of SIP operations do not need to be propagated 
into the PSTN.  The PSTN GW is the endpoint that originates or terminates 
SIP traffic.

Mike