[Asterisk-Users] Re: How to remove first ring tone on FXO?

[Jay Hennigan]

Aryanto Rachmad wrote:

> Thanks a lot Dean,
> 
> I think there is a way to remove that ring tone and also still have the
 > caller ID from the incoming call. I have been trying to find that on 
zaptel.c,
 > chan_zap.c and pbx.c, but I could not find that. Could you please let me
 > know which part of the codes handling that?

I don't see how this can be done.  The first ringback tone is sent from 
the serving telco CO, not from asterisk.

Sequence is:

1. CO sends one ringing pulse to the called party.  This both generates
an audible ring and wakes up the caller-ID modem to listen for CLID.
Simultaneously, ringback tone is played to the calling party.

2. CO sends modem burst with caller-ID information.

3a.  Call is answered by called party going off-hook and drawing loop
current.  Supervision occurs and audio is cut through.

3b.  Call is not answered.  Ringing voltage is sent every six seconds
as well as ringback tone to calling party until the calling party 
abandons the call or CO times out and releases.

In a loop-start FXO scenario the caller will hear the first ringback
which is generated by the telco switch in advance of your receiving CLID.

ISDN (BRI or PRI) will allow you to receive CLID in advance of audible 
ringing or ringback to the caller, but you aren't going to be able to do 
this with FXO.

-- 
Jay Hennigan - CCIE #7880 - Network Administration - jay at west.net
NetLojix Communications, Inc.  -  http://www.netlojix.com/
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