[Asterisk-Users] T1-PRI deployment questions...

[Steven Critchfield]

On Thu, 2003-05-29 at 15:06, Charles E. Youse wrote:
> On 29 May 2003, Steven Critchfield wrote:
> 
> > On Thu, 2003-05-29 at 10:44, Charles E. Youse wrote:
> > > B8ZS is required for PRI.  It's a digital service and can not handle the
> > > loss of data required for AMI.
> >
> > I wasn't aware that AMI lost data. AMI just inverts polarity on the line
> > for every other 1. B8ZS does the same thing but intentionally introduces
> > errors on the line to maintain 1's density. Neither one is lossy.
> >
> 
> AMI is lossy.  When the ones density in the signal is too low, AMI
> will insert ones to ensure that the far end does not lose sync.

As I understand it, AMI is not lossy but will may cause problems due to
not maintaining 1's density. 1's density is used to make sure both sides
are synced up properly. B8ZS is AMI except that it introduces bipolar
violoations to make sure the line doesn't stay in an off state for too
long.

So B8ZS intentionally throws errors on the line in a known manner so as
to make sure each side is in sync, but AMI does not care if the line
goes all 0's for a while.

I still haven't been able to dig up any documentation to back up that
AMI is lossy, just maybe prone to errors via slips.
-- 
Steven Critchfield  <critch at basesys.com>