[asterisk-users] Sangoma and BT single lines

[Steve Davies]

2009/4/6 Ed W <lists at wildgooses.com>:
> Hi, got a Sangoma A200 with a bunch of extension cards and having real
> problems getting it to deal with a normal single BT line

The A200 is a great card, and we use it quite a lot in the UK. Mostly
we use the A200D for the echo cancellation.

> Symptoms are that incoming calls are fine.  Outgoing calls ring the far
> end, BUT asterisk never sees that the call is answered (ie no message in
> the logs files saying so), as a result the remove end can hear the PBX
> side talking, but there is no audio back from the remote side to us.
> When we hangup the log files show messages thave suggest it thinks the
> line is still ringing

I think someone else already said that Asterisk sends the number using
DTMF, and then just opens up the audio channel - There is no answer
detection involved beyond the user hearing the ringtone stop and the
callee talking :)

> Comparing with another line which works fine (this is a BT multi-line
> system with what they call "PBX signalling" on it) I see that as soon as
> the remote end answers then asterisk gets a log message stating the same
> and audio is fine on this line

We have found that using "Residential" settings as a starting point,
and then asking for "Disconnect clear time" to be set to 800ms is all
that is needed. That one setting allows the hangup to be detected
reliably. We do also use the dialtone detection of Asterisk to be sure
we're dialling on a line that is ready to take a call.

> Have now spent nearly 4 months trying to get the signalling sorted on
> this line.  Most recently we requested "dual signalling" on the line -
> the end result is now that outbound calls work and asterisk reports that
> the phone answers, however, when you hangup the call then asterisk
> obviously gets a bunch of extra line reversals and things there is an
> immediate incoming call on the back of that outgoing call...

I would turn off any line reversal detection - We found it horribly
unreliable on BT's lines.

> Please - any suggestions on how to configure a Sangoma card for use with
> a normal BT single line?

Fundamentally, BT suffer from "backward compatability with the GPO"
syndrome, which basically means they do a load of stuff differently
from the rest of the world.
 - Only the caller can ever hang up a call involving an analogue party.
 - Many line timings such as DCT are different and so forth

Hope this is helpful...
Steve