[Asterisk-Users] PRI D-channel signalling error? "Ring requested onchannel 0/1 a lready in use on span 1. Hanging up owner."

[Peter Svensson]

On Tue, 28 Sep 2004, David Boyd wrote:

> > -----Original Message-----
> > From: asterisk-users-bounces at 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