[asterisk-users] Problem with incoming and outgoing calls via TDM

[Dave Fullerton]

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