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To: KailuaBoy who wrote (23114)	6/11/2000 10:26:00 PM
From: Frank A. Coluccio	Read Replies (1) \| Respond to of 29970

OT "It also keeps the clock sources in sync as in the case of B8ZS. Too many zeros and the slave clock source has no way to sync to the reference clock source" Bravo, KB! You're absolutely correct, and that's one of the primary reasons for maintaining sufficient ones. The other, being the preservation of electrical balance on the span, or system circuits. In the instance you cite, the voltage bearing ones (as opposed to zeros which are neutral potential, or zero volts with respect to common) are needed to "shock" the receive timing circuits with some degree of regularity. Although, today's "hardened" semiconductor-driven timing circuits can sustain far longer periods os "free-running" operation, without shocking, but the old rules from the original days of T1 still hold true, nonetheless. I suppose that this is for "just in case." I wasn't aware that you were as attuned to this trivia as you are. Kudos. There e are some subtle (and some not so subtle) distinctions, however, between the scrambling I first began discussing, and the introduction of B8ZS "ones" on a T1 digital span that you alluded to, which take place when insufficient ones exist in a stream of bits. In the former, the scrambling takes place regardless of any "ones densities" rules being violated, and this is done for optimizing the distribution of energy on digital spans (to prevent "singing" caused by skewing or biasing to one potential or the other. In the case of B8ZS( Note), on the other hand, bipolar signals are intentionally introduced onto the digital span in a way which would normally be considered "violations" (a form of coded ones) if it is determined that insufficient "ones" exist per unit time in a consecutive string of bits. For all intents and purposes, however, the same ends are achieved with respect to timing stability by both of these schemes. Thanks for that extra note. ---- Note: For the uninitiated, B8ZS stands for bipolar eight zero substitution. And it works like this: If a T carrier system sees successive bytes with eight consecutive zeros in them, the system will substitute those all-zero bytes with specially coded 'ones.' The coding consists of introducing some _unipolar_ "ones", in violation to the _bipolar_ rule (++Note), while maintaining over time an equal number of positive and negative going ones to maintain the timing discussed above. ++Note: The bipolar rule states, in oversimplified terms, that each successive "one" on the digital span will be of the opposite polarity to the one that precedes it. The first one would be positive going, the second one negative going, and so on. Binary zeros have no polarity, and are represented by zero volts. An intentional violation of this scheme, such as I referenced in the above B8ZS description, would consist of some coded combination of successive ones that were of the "same" polarity, in ways which the receive carrier terminal will recognize and translate back to eight zeros. FAC