[asterisk-dev] On PRIs, blocked channels, congestiona and telco technicians

Imran Ahmed codentest at gmail.com
Thu May 29 11:23:48 CDT 2008

On 5/29/08, Tony Mountifield <tony at softins.clara.co.uk> wrote:
> In article <20080529142043.GA24247 at k7.mavetju>,
> Edwin Groothuis <edwin at mavetju.org> wrote:
> > It has been discussed before here, unfortunately without result or
> > outcome.
> >
> > The issue? After about two months of operation, all 31 channels of
> > our PRI bcome, according to our telco, in a "blocked" state. What
> > that precisely means I am not really sure of, but all my SETUP PDUs
> > are answered with a RELEASE COMPLETE PDU:
> > [...]
> > < Protocol Discriminator: Q.931 (8)  len=9
> > < Call Ref: len= 2 (reference 3/0x3) (Terminator)
> > < Message type: RELEASE COMPLETE (90)
> > < [08 02 82 a2]
> > < Cause (len= 4) [ Ext: 1  Coding: CCITT (ITU) standard (0)  Spare: 0  Location: Public
> > network serving the local user (2)
> > <                  Ext: 1  Cause: Circuit/channel congestion (34), class = Network
> > Congestion (resource unavailable) (2) ]
> >
> >
> > Tomorrow I will be talking to a telco technician about this problem
> > and hopefully I can get the right data out of him to explain what
> > exactly happens and why their exchanges decide that a channel is
> > blocked.
> >
> > If somebody has a good question I can ask that technician which
> > could give me the right hint on where I could look for it in the
> > asterisk code, this is your chance...
> If you can capture the PRI debug over an extended period, it would be
> very interesting to know what the last activity was on a channel before
> it got blocked.
> When Asterisk does its hourly reset of idle channels, do the blocked
> channels get included?

My 2 cents:

We had the same issue  before with global crossing, If you notice
asterisk would automatically try to reset the channel after the
release complete is received, which is successful, but the telco's
switch still refuses to unblock the channel, the switch does not send
any incoming calls on the blocked channel either.

On some occassions when we detected the problem, we got the telco's
tech online and asked them to reset just that channel from their side,
and then channel started working fine.

After all the debugging and tracing, we had concluded that it was a
telco's switch issue, and had to bear with it until we switched
carriers and we don't have that issue any more or may be we do, but
haven't yet detected it.


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