[asterisk-users] Ghost in the Channel-Banks

[Martin Lima]

On Thursday 18 December 2008, Justin Phelps wrote:
> I've been struggling with an ongoing problem the last month.
>
> Here is the layout of the wiring:
> T1 from ISP > DiTech Echo Cancel device > Voice Channel-Bank
>
> (same) T1 from ISP > (same) DiTech Echo Cancel device > asterisk1 server
> zap card > fax channel bank
>
> (same) T1 from ISP > (same) DiTech Echo Cancel device > asterisk1 server
> zap card > asterisk2 server
>
> Now, let me explain the symptoms.
>
> d-channel errors on the asterisk1 server on span1 (which is the line
> coming from the echo cancel from the ISP). asterisk2 server isn't being
> used as far as I can tell. I've got a red alarm on the port on asterisk1
> that asterisk2 is plugged into.

I would bet your "asterisk2" server was meant for some kind of transition to a 
different setup. Is there at least some dialplan inside? sip.conf? iax, 
voicemail etc...?

> faxes through the fax channel bank are working most of the time. There
> seems to be problems with multipage faxes. Not isolated to a particular
> port on the channel bank. As I understand it, echo cancel for faxes is a
> bad thing, so I don't understand why the previous IT Admin here setup
> the system as such.
Some echo cancellers detect a fax transmission and turn echo cancellation off. 
In your case if I understand your setup correctly such a device is ambiguous 
at the best... Possibly it used to be another set of voice lines converted to 
fax without changes in configuration?
I dont really understand the role of echo canceller on E1/T1...

> Some voice phones on the voice channel banks were not recognizing tones
Why the phone should recognize tones? It just generated them while dialing.

> when dialing. That seems to have been resolved after power cycling the
> channel bank a few times, and restarting asterisk2 (odd that there
> doesn't seem to be anything active on asterisk2)
Looks like some strange ground loops in your wiring, power issue or something 
similar.

> I've been working with the ISP on the d-channel stuff, and things seem
> to get a little better as they reset equipment, but the d-channel errors
> have not gone away.
Some as above...
BTW they will always tell you they "reset something" no matter what they have 
really done... :-)

> I really need advice on these problems. From what I've said, where do
> you think the problem lies? in the channel banks? in the echo canceller?
> in the asterisk2 or asterisk1 server? With the ISP?
Hard to guess without deeper knowledge of your setup. Intermittent errors and 
hardware lockups are often caused by power conditions, potential differences 
and spikes in the powerline. (two pieces of equipment connected together but 
plugged into two different power outlets coming from two opposite ends of the 
building can cause real headache!) Check it first. Then you may want to 
continue what your former IT admin tried to start.... :-)

Martin