<snip>
>There is a fourth method, which is used for supporting the ISDN D
channel
and SS7 A-links over AMI lines. It's called "inverted HDLC." The
idea is
that since normal HDLC data cannot have a run of more than 6 ones
in a row
(the frame mark is 01111110, and no legal code has more ones), if
you invert
each bit you get a stream which has no more than 6 zero bits in a
row, which
is sufficient ones-density for an AMI line.
Wow, this is the first I have ever heard of this. Who makes
equipment to support this?
>This allows you to carry 64K sync data on a timeslot of a line without
requiring B8ZS support.
>I don't know if anyone is using this for transport of user-level
data, though.
There's no technical reason it couldn't be used this way, but it is
probably
not worthwhile given the availability of B8ZS lines.
I am not aware of any.
>(And, of course, it should be noted that T1 lines are full-duplex.
Always.)
One nit here - T1's are actually two way simplex, not full duplex.
Data only travels in one direction, and there are 2 paths to create
"full duplex".
Kyle Platts
CSS-Tech
!NTERPRISE Networking Services