[Asterisk-Users] How to fix a Blue Alarm?? Line Noise?

[Peter Svensson]

On Thu, 11 Aug 2005, Geoff Manning wrote:

> We are having line noise issues in our Asterisk to legacy PBX integration.
> All SIP calls originating from IP phones sound crystal clear. All calls that
> originate from the legacy PBX (Isoetec 228) and route through the Asterisk
> and out SIP have a lot of line noise.
> 
> I believe I have it pinned down to these Blue Alarm errors that I can see on
> the legacy PBX side. zttool shows no alarm but when I view the T1 stats on
> the Isoetec I see numerous Blue Alarms.

A blue alarm sounds really strange. That indicates that the remote end
(asterisk) in this case does not want to play at all. On a T1 it is sent
as a continous series of unframed 1:s. I am not sure if asterisk ever
sends a blue alarm (Alarm Indication Signal). 

Receiving a blue alarm is indicative of a serious problem. There should 
not be any audio at that time, since the blue alarm is actually a long 
unframed signal.

Peter