asterisk users - Mar 2009 - Problem with incoming and outgoing calls via TDM

Hello all.

Please, I'd like to know if somebody can help me with this problem.
I have successfully configured a PBX with Asterisk 1.4 and a Digium analog card
with 4 ports.

This PBX has a lot of incoming and outgoing calls, and works perfect in general,
but there are some extrange cases where an incoming call is bridget with an
outgoing call, and the caller that is calling TO the PBX can even hear the dtmf
tones of the caller that is calling OUT the PBX, and due the high traffic this
is happening a lot.
It seems that asterisk is taking the zap channel to call out in the exact moment
before it is marked as busy with the incoming call.
Please, is there any configuration to avoid this?

Thanks a lot in advance.
Rosa.


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Rosa De Santis wrote:
> Hello all.
> 
> Please, I'd like to know if somebody can help me with this problem.
> I have successfully configured a PBX with Asterisk 1.4 and a Digium analog
card with 4 ports.
> 
> This PBX has a lot of incoming and outgoing calls, and works perfect in
general, but there are some extrange cases where an incoming call is bridget
with an outgoing call, and the caller that is calling TO the PBX can even hear
the dtmf tones of the caller that is calling OUT the PBX, and due the high
traffic this is happening a lot.
> It seems that asterisk is taking the zap channel to call out in the exact
moment before it is marked as busy with the incoming call.
> Please, is there any configuration to avoid this?
> 
> Thanks a lot in advance.
> Rosa.
The situation you're referring to is called glare. You'll find 
discussion of it in the archives and on voip-info.org. You need to make 
sure you are seizing lines for outgoing calls in the reverse order that 
they are used for incoming calls. Check out the G dialing option for 
Zaptel/DAHDI channels (under Dialing a Group section):

http://www.voip-info.org/wiki/view/Asterisk+ZAP+channels

If this doesn't work, your next best bet is to increase the number of 
lines you have.

-Dave

On Wed, 11 Mar 2009, Rosa De Santis wrote:
>
> Hello all.
>
> Please, I'd like to know if somebody can help me with this problem.
> I have successfully configured a PBX with Asterisk 1.4 and a Digium analog
card with 4 ports.
>
> This PBX has a lot of incoming and outgoing calls, and works perfect in 
> general, but there are some extrange cases where an incoming call is 
> bridget with an outgoing call, and the caller that is calling TO the PBX 
> can even hear the dtmf tones of the caller that is calling OUT the PBX, 
> and due the high traffic this is happening a lot. It seems that asterisk 
> is taking the zap channel to call out in the exact moment before it is 
> marked as busy with the incoming call. Please, is there any 
> configuration to avoid this?
It's called "glare" and your options to "fix" it partly
depend on what
country you are in. I don't think it's totally fixable with analogue 
lines.

Make sure you have the right country code specified in /etc/zaptel.conf 
and are using "Kewlstart". Eg. for the UK:

fxsks=1
fxsks=2
fxsks=3
fxsks=4
loadzone=uk
defaultzone=uk

Your options are to replace the 'ks' with 'gs' or 'ls' -
but others might
be able to advise you what's best for your country/telco.

But do make sure your incoming calls start at one end, and outgoing start 
at the other - so if the first line is connected to port 1, 2nd to port 2, 
etc. you want to dial-out starting at port 4 - that's the capital G option 
in dial - eg. dial(Zap/G1/xxxx...) the lower-case g will start outbound 
dialing at the lower port number. (And put the lines in the right group in 
/etc/asterisk/zapata.conf)

Another solution might be to get more channels - are your users & callers 
complaining of busy tones?

Gordon