[VoiceOps] Strange Call Flow

[anorexicpoodle]

The differences you have outlined for 180 and 183 aren't necessarily
accurate.

180 means the called party is being alerted. It is perfectly legal to
send a 180 w/ SDP specifying the called party will provide ringback.
Generally you will only see a single 180 message in a dialogue since the
EP can only begin ringing once.

183 messages just contain progress updates to the session, so they can
happen both before and after the 180, if a 180 is sent at all (i often
see 183 w/sdp, and ringback provided by the far end in lieu of a
straight 180 or 180w/sdp). 

For example, if you send an invite to a B2BUA it could send the invite
to EP 1, send back a 180, then have EP1 timeout, so it cancels the
dialogue and invites EP2, so it could send a 183 back to the initiating
party to indicate something changed (with or without media control).

Yes there is a lot of ambiguity here. YMMV etc etc. 



On Fri, 2010-10-15 at 14:17 -0500, Hiers, David wrote:

> 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
> 2525 SW 1st Ave.
> Suite 300W
> Portland, OR 97201
> o: 503-205-4467
> f: 503-402-3277
> 
> 
> -----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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