[asterisk-users] Zap Channels Collide (Incoming & Outgoing)

[C. Chad Wallace]

At 5:22 PM on 08 May 2008, Forrest Beck wrote:

> I have a client that is using the Sangoma A200DE with two phone
> lines attached.
> 
> The problem is:
> 
> They use their phone (Grandstream GXP2020) to dial out of the system.
> Instead of getting ringing, there is someone on the other end of the  
> line that happened to dial in at the exact same moment.
> 
> So now they are stuck talking with this person, instead of the one
> the originally called.
> 
> The ZAP channels are in a dial plan context that instructs it to
> just dial the office phones.
> 
> [zap1]
> exten => s,1,Dial(SIP/1001&SIP/1002&SIP/1003)
> exten => s,n,Voicemail(1000 at vm)
> 
> Anyone know how to get around this?

This is known in the telephony world as "glare", and there's not much
you can do about it, especially if you only have one line.

If you have multiple lines on an over-ring (or hunt group or whatever
you call it), the best thing to do is find out which way the telco
assigns calls to those lines wrt how they are assigned to the Asterisk
box.  And then allocate outgoing calls in the other direction.  

On our installation, the calls are allocated from the first FXO port
(Zap/25) up.  So we set Asterisk to dial out starting from the last FXO
port in the group by calling Dial(Zap/G2) (capital G means dial down
from last, lowercase g means dial up from first).  That minimizes glare.

But, as I said before, if you only have one line, you can't do that...

-- 

C. Chad Wallace, B.Sc.
The Lodging Company
http://www.skihills.com/
OpenPGP Public Key ID: 0x262208A0

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