Re: (ASCEND) Re: Clocking question

[Phillip Vandry <vandry@mlink.net>]

> You need to take timing off a PRI, then have the telco have the rest of the
> circuits take timing off you ("loop-timing"). You may be able to get away
> with not doing this if all your circuits are from a single telco, but when
> you start terminating circuits from multiple vendors in a single chassis it
> becomes critical.

I don't think most telcos are willing to do this :-(

As I understand things (I may be wrong), they have good reason not to.
If your PRI terminates in a Mux of some kind (say, to backhaul it OC3
or OC12 into the CO), the Mux probably does not have pleisiochronous
hardware (i.e. it cannot buffer and adjust the signals to match the
various clock rates coming from its various input and output ports), so
it is probably forced to clock off its aggregate port (to the CO) and
supply the clock to all the other ports. And the aggregate port clocks
off the CO's redundant master clock at the other end. If your PRI goes
straight into the switch, I still don't think you could necesarily do
it, or, at least, you'd have to have a common clock on all the ports
on a single linecard (how many ports are there on a DMS 100 T1 linecard,
anyway?).

Am I way off?

-Phil
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