[asterisk-users] Ghost in the Channel-Banks

[Jerry Jones]

On Dec 22, 2008, at 10:38 PM, Martin Lima wrote:

> 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...?
Something does not fit here. If you have the T1 from the ISP going to  
the echo can, then it cannot go to more than one device. It is not a  
MUX as far as I remember, have used to great effect in past. Each T1  
in matches up to a T1 out.
>
>
>> 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...

Guarantee the Ditech deteects fax and cancels echo can. However any IP  
in FAX path is problematic for most FAX. If possible turn off ECM. If  
symptoms are mainly on a single fax machine make sure you have enough  
memory to buffer entire fax. Some systems let you print as they come  
in, but I have also seen some which are still trying to buffer while  
printing and run over. This showed up with a mortgage company doing 50  
page legal forms. First 20 or so were fine then started bombing.
Best method I have found to troubleshooting FAX is to use a machine  
which generates a T30 trace output upon completion.

>
>
>> 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... :-)

Again if this is a PRI, how is signalling being done for 2 T1  
connections when only one D Channel. I suspect a partial PRI?
>
>
>> 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.... :-)

Are D Channels mostly working just intermittant? I assume you have  
Ditech set for passthrough on these channels? ie no echo cancel?
>
>
> Martin
>
>
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