[Asterisk-Users] T1 slips/BPVs clarifications (was: Help! Problems talking to upstream switch)

[Don Pobanz]

Just some clarification here.

On Monday, June 30, 2003 12:04 AM, Steven Critchfield 
[SMTP:critch at basesys.com] wrote:
>
> As for slips and bipolar violations...
> T1s are just high speed serial lines. A sleep is when you loose sync
> with the far side and when you see a 1 come across the line, you may
> not
> know which bit it was for.

A slip is when one end of the circuit is running according to a clock 
that is faster than the other end. Once the capacity of the buffer 
overflows a frame (193 bits) is discarded if the far end clock is 
running faster or a frame is repeated if the far end clock is running 
slower.

It is called OOF (out of Frame) if sync is lost with the far end and 
the system must retrain to find the framing bits.



> This would be a slip. Bipolar violations are
> a part of the signaling, but can also be errors.

I believe the word 'signaling' was used here by mistake. Bipolar 
violations are not related to signaling. In the B8ZS case they are 
intentionally used as part of the line coding.

> A T1 alternates the
> polarity of the 1 pulse to allow the line to run farther on lower
> voltage. Just doing alternating polarity is AMI or Alternate Mark
> Inversion. A bipolar violation is when a bit is received as the same
> polarity as the last bit received. On an AMI line a bipolar violation
> is
> an error. On a B8ZS, bipolar violations are intentionally inserted
> into
> the line to keep the line from transmitting too many 0's in a row and
> contributing to a slip.

Too many 0's don't contribute to a slip but contribute to a LOF (loss 
of frame).

> When set for B8ZS the "error" is somewhat
> expected and ignored.

Some errors are expected and the expected errors do not count as a 
bipolar violation. There can also be bipolar violations on a B8ZS line 
coded T1.

Don Pobanz