Re: 56k Required encoding

Kyle Platts (kwplat1@reliant.uswc.uswest.com)
Thu, 31 Jul 97 10:39:46 -0500

>AMI is not a good choice for a data circuit, and I'm not sure the =
PM3 even
supports it. It has been some time since I was around the details =
of
this, but as I remember it, AMI does not have enough line =
transitions to
allow proper clock recovery. Unless the line is very busy (to =
keep
transitions high) you will get errors on the link. B8ZS forces a =
high
enough line transitions rate through enforced bipolar violations =
to allow
decent clock recovery, and should always be used on a data =
circuit.=20

What the heck are you talking about? AMI robs the least =
significant bit in each timeslot and sets it to a 1 ensuring ones =
density to recover clock from the line. It might even be argued =
that AMI is better than B8ZS at maintianing synchronization on a =
T1. With B8ZS, when a string of 8 zeros is encountered (which is =
very common when sending ACTUAL data) a bipolar violation occurs =
on the line and a special bit pattern is inserted.

The downfall of AMI, is that it only supports 56k timeslots as =
opposed to 64k timeslots which can be acheived with the use of =
B8ZS. =20

Kyle Platts
CSS-Tech
!NTERPRISE Networking Services