Don Pobanz wrote:
When I was looking at timing before this is the conclusion that I have
come to.
The T400P card has an internal clock that all four T1s of that card
will be timed off of. This internal clock can be free running (not
referenced to any other clock) or reference to another clock (the clock
on the other end of a T1 line). This is set up in Zaptel.conf
span=<span num>,<timing>,<line build out>,<framing>,<coding>
Important points.
1. All T1s of a T400P run off of the same internal clock.
2. The internal clock can be free running - not reference to any
other clock.
You can only use this for a single card within a private network,
unconnected to the public network. In that case you can make that one
card free run, and it becomes the network master. All the others must
slave to it.
3. The only other reference the clock can use is timing from an
incoming T1. If the primary clocking T1 is down then it can be set to
use a secondary T1 to derive timing (or 3rd or 4th)
This is what 99% of people need. The public network will not sync to
you. You must sync to them. Public exchanges actually use rhubidium
atomic clocks, so their clock is darned accurate (just like the line
scan rate of your TV signal, and for similar reasons).
4. There is no way to time off of an external clock be it stratum 3
or 2 or whatever (unless it is part of a T1 thereby burning up a T1
port in the T400P card).
Stratum 3 is a term I normally associate with NTP. This is a
macroscopically accurate clock. A clock accurate at the cycle level is
needed to keep a T1 flowing right.
5. If the system has 2 T400P cards the clocks will not be timed to
each other (unless each has an incoming T1 with the same timing.)
If you are smart this will probably be the case. Make one of the T1s on
each card a line from the public network, and use 1 to 3 of the others
for private network lines. All those T1s comming in from the public
network, even from different carriers, will be in isochronous, so you
will never get slips this way. It would have been nice if Mark had
provided a link wire facility between the cards, to keep them all in
step under all conditions, but life is never perfect. :-\
Regards,
Steve
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