[asterisk-users] PRI Test Lab

[Kevin P. Fleming]

Matt Florell wrote:

> Can you tell me where the setting is to force Master timing on Digium
> cards per port? I really didn't think Digium cards had the ability to
> force Master in this way. I've tried to do it with channelbanks before
> and couldn't force it to master, whereas I can get it to work with
> Sangoma.

I'm not sure that the terms you are using match what I'm used to hearing
and telling people, so let me try to describe how our cards work and you
can tell me how that matches up with what you want to do.

Digium multi-port T1/E1 cards use a single clock source for transmitting
on all connected spans. That clock source can be on the onboard
oscillator, or the recovered clock from one of the spans, and the source
selection can change dynamically based on the configuration (in other
words, you can set the first span as 'highest priority', the second span
as 'second priority', etc). If a span is selected to be the clock source
for the entire card, and then that span goes into red alarm, a different
clock source will be chosen, until that span recovers.

So, what this means is that each span port that is configured to be used
is *always* transmitting a bit stream, and due to the nature of T1/E1
signaling, that bit stream includes a clock. A device connected to that
port will *always* be able to recover a clock from that bitstream if it
chooses to do so. For channel banks, other servers, downstream PBXes,
etc. this is a common configuration, and the device will derive its
clock from the bitstream it receives from the Digium card.

In cases where the system admin is using spans that are generated from
'upstream' devices, where the card should slave its transmitted clock to
the recovered clock from that span, then the card can be configured in
this mode. Once a span has been selected to be the clock source for the
card, *all* the spans on that card will use that clock source for their
transmitted bit streams.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kpfleming at digium.com
Check us out at www.digium.com & www.asterisk.org