[VoiceOps] Strange Call Flow

[Hiers, David]

As far as I can tell, that signaling is legal, but somewhat nonsensical.

The UAS can send as many 1xx responses as it wants, and  3261 contains no language that precludes sending 183 after 180.

The nonsense part comes from the meaning of 180 and 183.  180 means "play local alerting tone", and 183 means "play remote alerting tone", so you're changing a pretty basic structure on the fly.

The gestalt of draft-ietf-sip-183-00.txt seems to be that you'll provide either 180 or 183, not both, so I can see where a UAC would choke on it.



David Hiers

CCIE (R/S, V), CISSP
ADP Dealer Services
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-----Original Message-----
From: voiceops-bounces at voiceops.org [mailto:voiceops-bounces at voiceops.org] On Behalf Of Tim Donahue
Sent: Friday, October 15, 2010 10:49 AM
To: voiceops at voiceops.org
Subject: [VoiceOps] Strange Call Flow

I'm seeing a strange call flow from a client with a Cisco CUBE setup.
This is happening when they attempt to forward a call from their system
to a PSTN line.

SBC                          CUBE
 | ----------INVITE---------> |
 | <------100 Trying--------- |
 | <------180 Trying--------- |
 | <--183 Session Progress--- |
 | <--------200 OK----------- |

I've never seen a call setup that switched from a 180 Ringing to a 183
Session Progress mid-setup before, and it seems to be doing funny things
to the media transport through our SBC (we see audio come in from one of
the call legs but it doesn't get forwarded to the other call leg).  Is
this a legal call flow that we should add to our tests when evaluating
new hardware?

Has anyone seen problems like this before?

Tim
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