[asterisk-users] "alaw = 1-2" in system.conf (dahdi) not working in UK

Sebastian Arcus shop at open-t.co.uk
Sun Mar 11 13:49:01 CDT 2012

On 11/03/12 14:07, Tzafrir Cohen wrote:
> On Sun, Mar 11, 2012 at 12:05:48PM +0000, Sebastian Arcus wrote:
>> Hi all,
>> I've tried to explicitly set my two PSTN trunks/FXO lines to alaw with:
>> alaw = 1-2
>> in /etc/dahdi/system.conf. However, when I do this, all I get is
>> loud intense noise on the line and nothing else - can't dial, can't
>> make calls, can't receive calls. If I omit it altogether, everything
>> works fine.
>> As I'm in the UK - I thought Europe uses alaw on phone lines
> No, they don't. Phone lines are analog. ulaw / alaw settings here are
> internal to DAHDI. The digital PCM gets converted to analog "audio"
> (voltage level) on the adapter.
>> - how
>> come Asterisk seems to be using only ulaw - and alaw won't even
>> work? Config examples on the Internet seem to suggest that it should
>> work.
> Though it is, indeed, a bug.

Thank you Tzafrir. I initially though that the signal being analog, it 
can't be encoded with a digital compression algorithm - but as config 
examples online kept on suggesting the setting - I thought I would try it.

Linux vehicle CCTV - www.open-t.co.uk/iroko

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