ISDN BRI S/T line-code violation

hi guys: When i read CCNP Remote Access study Guide,it's say that Logic zero bits are denoted by the presence of a +1 or -1 volt pulse. Logic one bits are denoted by the absence of a pulse. Each logic zero bit will alternate in polarity with respect to the previous pulse. A line-code violation is declared when two consecutive pulses remain at the same polarity.MY question is:in previous figure,on the s/t to nt1 direction,the DC Bits is -1 pulse,why the first B1 bits can be presence of -1 pulse,will not so cause line-code violation?

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Right. This is called "Alternate Mark Inversion" or "AMI"

Right, decause it assume you must have missed one.

Uhhhh... What figure? Your question makes no sense.


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will help you? The start of frame is marked with an AMI line code violation which ensures there is no DC signal and makes a clear start of frame.

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Phillip Remaker

Thanks for you reply,because the group can't display figure,so can i send the figure to you by email?

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