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

[Al Baker]

I know that everyone has gaps in their knowledge, but I am just 
staggered that
systems are being sold/deployed with such fundamental TELCO workings not 
being
understood.  Frightening.

C. Chad Wallace wrote:
> 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...
>
>