asterisk users - Sep 2004 - PRI D-channel signalling error? "Ring requested on channel 0/1 a lready in use on span 1. Hanging up owner."

Can anyone shed some light on "Ring requested on channel 0/1 already in use
on span 1.  Hanging up owner."? This is happening two or three times a day
on a span with about 500-600 calls per day. The remote device is a PBX,
connected by a crossover cable and protocol is DMS-100.

Thanks.

Kris Boutilier
Information Systems Coordinator
Sunshine Coast Regional District

> -----Original Message-----
> From: asterisk-users-bounces@lists.digium.com
> [mailto:asterisk-users-bounces@lists.digium.com]On Behalf Of Kris
> Boutilier
> Sent: Tuesday, September 28, 2004 4:00 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: [Asterisk-Users] PRI D-channel signalling error? "Ring
> requested onchannel 0/1 a lready in use on span 1. Hanging up owner."
>
>
> Can anyone shed some light on "Ring requested on channel 0/1
> already in use
> on span 1.  Hanging up owner."? This is happening two or three times a
day
> on a span with about 500-600 calls per day. The remote device is a PBX,
> connected by a crossover cable and protocol is DMS-100.
>
> Thanks.
>
> Kris Boutilier
> Information Systems Coordinator
> Sunshine Coast Regional District
>
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Sounds like it could be glare, is the span two way?

Dave

On Tue, 28 Sep 2004, David Boyd wrote:
> > -----Original Message-----
> > From: asterisk-users-bounces@lists.digium.com
> >
> > Can anyone shed some light on "Ring requested on channel 0/1
> > already in use
> > on span 1.  Hanging up owner."? This is happening two or three
times a day
> > on a span with about 500-600 calls per day. The remote device is a
PBX,
> > connected by a crossover cable and protocol is DMS-100.
> 
> Sounds like it could be glare, is the span two way?
The q931 specification (5.7) seems to say that there can be a conflict of 
channels, if both the cpe and the net selects the same B channel for one 
call each at the same time. I guess this can be prevented if the cpe 
allows the net to select the B channel for the outgoing calls (Any Channel 
Acceptable).

Barring that, a contention can occur and is handled by the cpe side 
clearing its still unconnected call. The cpe side could retry the call on 
a different B channel at that point.
>From q very quick look at chan_zap and the messages from a pri intense 
debug it seems that Asterisk selects a B channel and requests that 
particular channel from the net. 

For the normal isdn configuration (the net hunts from low channels, the 
cpe hunts from high channels) there should rarely be a collision unless 
the trunk is close to saturation, in which case congestion _is_ the 
correct result.

Peter