Clear Channel on a T1

Good point, Phil. I believe that the modern T1 spec states that a maximum or 45 zeros can be sent before the CSU will inject a '1'. I don't have a spec handy to verify it.

Of course, with B8ZS, you'll never approach this long string of zeros on the line, so it's a moot point. B8ZS replaces eight zeros with 4/4 ones/zeros, in a known bipolar violation pattern. This will insure that ones' density is met on the line, and the circuit endpoints can replace the injected ones with eight zeros and restore the bit patterns of the modified DS0s.

It's also the source of grief when a telco provisions one segment of a T1 circuit without B8ZS. When this non-B8ZS segment sees too many zeros, ones will be injected in the stream, corrupting the data.

Of course, this NEVER happens anymore...right? :wink:

-rb

<Bell Atlantic Tech> "If it's a T1, then it's B8ZS"
<Me> "Then why can't I send all zeroes, but every other pattern works?"
<Bell> "Hmm... lemme check...(pause)...try now"
<Me> "Ok, it's working. Did you find an AMI segment?"
<Bell> "I didn't change anything."

Ticket closed, "No problem found".

-C

<Bell Atlantic Tech> "If it's a T1, then it's B8ZS"
<Me> "Then why can't I send all zeroes, but every other pattern works?"
<Bell> "Hmm... lemme check...(pause)...try now"
<Me> "Ok, it's working. Did you find an AMI segment?"
<Bell> "I didn't change anything."

Ticket closed, "No problem found".

In BT speak (in the UK) this is a "FNF" - Fault Not Found.

Notice the useful tense used there - so if later a fault is actually proven,
then the phrase means something different to the normal immediate
understanding people hear. I wonder how many marketing people they roped in
for this engineering process. 30 years ago.

(If people don't see what I mean, think "A fault was not found" vs. "The
fault was not found".)

Peter