[Asterisk-Users] TE110P flashing red/green when PRI connected

[Peter Svensson]

On Tue, 9 Aug 2005, Fredrik Lithén wrote:

> Yes, I tried that but it sent me a bit offtrack as it reported "blue"
> which I assumed was a clocksync problem, or at least, that was the info
> I could find.

As far as I can tell zttool/zaptel uses the term BLue Alarm for the E1
term AIS (Alarm Indication Signal) which is a layer 2 signal sent by
someone in the receive path (not necesarrily the PSTN end itself)  
indicating that no valid incoming signal is present. 

A bitstream is present at the receiver, though it is unframed and invalid
(i.e. the receiver is seeing a transmitter that does not quite know what
to transmit). This is different from a red alarm where there is no
bitstream at all.

One common cause for the blue alarm is when the PSTN end shuts down an 
interface that has many errors. This si common practice and is probably 
what happend when there was a mismatch in the crc setting. 

> As it turned out, my provider didn't have error correction enabled so
> after have endured painstaking task of getting hold of the right
> person to talk to :) the problem was swiftly fixed.

An additional point: in the original post you mentioned that your zaptel 
line looked like 
  span=1,0,0,ccs,hdb3,crc4 
which should almost certainly be
  span=1,1,0,ccs,hdb3,crc4 
since you want to synchronize your clock rate to that of the PSTN 
provider. With your old setting you will occasionally get a slip. Normally 
not a major problem, but it can wreck havoc with data transmissions 
(Unrestricted Digital) or in some cases with the D channel signalling.

Peter