[Asterisk-Users] Two zaptel T1 cards: no clock from one

[Lyle Giese]

It is not important to have clocking between cards. Clocking is to make sure
everyone knows how long a T1 frame should last and everyone is doing it
exactly on schedule.

The problem is that for the most part a frame is buffered. So while the
DS0's are being processed, you don't have a new frame overwritting the old
info before it's read or the DS0 buffer is read twice.  If the timing
between the two T1's is off that is a problem and that's called a slip.
Either in reading the buffer, you get the same info twice for a certain
voice channel or you miss reading and the buffer is overwritten before your
card reads it.

When you have two cards, you need to make sure that you are taking timing
for the card from a good source.  If you are connecting to a telco, they
should all be good sources of timing and you shouldn't have any problems.

Probably another concept that is confusing is that timing is not syncing the
start and stop of the T1 frame, but really syncing the amount of time
between the start and finish of that frame.  Because the time to get the
signal from point a to point b varies from the amount of time to get a
signal from point a to point c, we cann't( and don't ) depend on the T1
frame starting at the same time.  It's really about filling the buffer and
having the correct amount of time to read it without overwriting it before
it's read or reading it twice.

Lyle
----- Original Message ----- 
From: "Kevin Blackham" <blackham at gmail.com>
To: "Asterisk Users Mailing List - Non-Commercial Discussion"
<asterisk-users at lists.digium.com>
Sent: Saturday, December 04, 2004 5:00 PM
Subject: Re: [Asterisk-Users] Two zaptel T1 cards: no clock from one


> Yeah, proper crossover cable.  I've eliminated all cabling issues with
> the T1 analyzer.  I get a full and accurate pattern back when I test
> from the cable end where it would have been connected into the T100P,
> with the channel bank in loopback.  The main symptom is that when I
> hook the analyzer directly to either the channel bank or the T100P,
> neither is providing clock.  I could have the channel bank supply one,
> but I will have fax/modem calls bridged between the two PCI cards, so
> a common clock is best.  The most disturbing thing is that the T100P,
> as the only card in a system, provided clock just fine.
>
> There was a thread last month in -dev about being unable to use common
> clock source across cards.  Is this related?  How can one cause zaptel
> to provide ref clock?  Should I be seeing 1000 interrupts/sec on any
> and all TDM cards?
>
> On Fri, 03 Dec 2004 23:59:22 -0500, [email protected] wrote:
> > The cable should be cross-connect 1-4, 2-5 each way. Is it?
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