🚀 go-pugleaf

In article <4cslp6$ia8@rtpnews.raleigh.ibm.com>, lmarks@vnet.ibm.com  (Laurence V. Marks) says:
>
>In <tsw-0801961308380001@cypher.3do.com>, tsw@3do.com (Tom Watson) writes:
>>In article <4cec6n$fm7@mercury.near.net>, fgoldstein@bbn.com (Fred R.
>>Goldstein) wrote:
>>
>>> 
>>> A conformant CSU for "AMI" (better known as AMI/ZCS, for Zero Code
>>> Suppression) coding will  NEVER send the 15 zeroes, and WILL insert
>>> a zero if the source doesn't conform.  Thus the alarm means the CSU
>>> is not working or connected -- a disconnected wire looks like a
>>> string of zeroes, no?
>>> 
>>
>>Isn't B8ZS where AMI violations are put in when it senses 8 zeros.  The
>>receiver then notices this and puts the zeros back to the channel unit.
>>
>>The violations were: 0++00--0 and 0--00++0 depending upon the previous bit
>>signalled.
>>
>
>Tom,
>
>You have it right.  Fred is addressing the case of an older span that 
>has not yet been converted to B8ZS.  In this case the customer's CSU
>is responsible for forcing ones into every 8-bits if his other 
>equipment fails to do so (the old no-harm-to-the-network philosophy).
>
>Since you might have a one at the beginning of one 8-bit channel, and
>at the end of the next, you could have up to 15 zeros in a sequence. 
>T-1 equipment sends an alarm condtion if there are more than 15 ones 
>in sequence.
>
>Laurence V. Marks
>IBM Corp. - Research Triangle Park, NC
>


I'll add my two cents to this. All of the above is "partially" correct.
First, the USER / INSTALLER of a CSU has to option the CSU to
enforce 62411 pulse density issues. (inserting binary 1's
as appropriate to insure pulse density requirements are met.)
I have seen CSUs where both the 15 consecutive zeros and 12.5% 
criteria are independantly configured. These options are always
seperate from any AMI-(yes/no) or B8ZS-(yes/no) functionality
which is also an OPTION that a user /installer must define appropriately.


By the way, there is NO alarm that is "transmitted" on a span if 
16 zeros should ever be detected. The machine "detecting" 16 zeros
may blink an LED or increment a counter or perform some other LOCAL
indication at the device itself - but no specific bit pattern is
generated and sent up/downstream to indicate "excessive zeros".

Going back to an (the first) earlier post on this subject, a YELLOW
actually is a bit sequence that is transmitted, but NOT for "excessive
zero" conditions. Yellows are transmitted in an "upstream" direction
when "out of frame" conditions occur. On a "D4" span, "yellow"
could be a "binary 0" condition in the second most significant
bit of each timeslot - or - a terminal framing bit set to "0" in the
last frame of a superframe - or - a repeating eight 1's and eight 0's
on an ESF span. In other words, this too is configurable by the USER
on many products, and may not be enabled at all!

FYI, B8ZS words look like "000+-0-+" or "000-+0+-" depending upon the
polarity of the last "legitimate" pulse before an
"all zero" octet was encountered.


Thank you.
I'll go to sleep now.    :-)

ja