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

Sebastian Arcus shop at open-t.co.uk
Sun Mar 11 16:09:59 CDT 2012

On 11/03/12 18:57, Shaun Ruffell wrote:
> On Sun, Mar 11, 2012 at 06:49:01PM +0000, Sebastian Arcus wrote:
>> 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.
> Hi Sebastien,
> If for some reason you do need it to be in alaw, i.e. sometimes you
> can get bettwe results when bridging to a digital line in alaw mode
> if the audio is originally companded to alaw on the analog card, you
> can use the 'companding' or 'alawoverride' module parameter
> depending on the analog card that you're using.
> There is an old open bug for this, DAHLIN-58 [1], which will require
> a board driver / core of dahdi interface change to allow the board
> drivers to be notified when the companding mode on a channel is
> changed.
> [1] https://issues.asterisk.org/jira/browse/DAHLIN-58?focusedCommentId=177136&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-177136
> Cheers,
> Shaun

Thanks Shaun. I'll keep this in mind in case it is ever needed.

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

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