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

[Steven Critchfield]

On Mon, 2003-06-30 at 13:07, Don Pobanz wrote:
> Just some clarification here.

Thank you for the corrections.


> 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
> _______________________________________________
> Asterisk-Users mailing list
> Asterisk-Users at lists.digium.com
> http://lists.digium.com/mailman/listinfo/asterisk-users
-- 
Steven Critchfield  <critch at basesys.com>