T1: A Survival Guide

Errors

Errors are the building blocks of the whole system. Here is a list of errors, which are summarized in Table C-4:

Bipolar violation (BPV)

When used as an error counter, BPVs refer only to unintentional BPVs. BPVs inserted by the B8ZS line code are not counted as errors. Thus, on AMI-coded links, any occurrence of two consecutive identical-polarity pulses is counted. B8ZS-coded links, on the other hand, count only BPVs that are not part of the zero-substitution code.

Excessive zeros (EXZ)

Line codes also specify a maximum number of consecutive zeros: 15 for AMI-coded links and 7 for B8ZS. Longer strings of consecutive zeros indicate a problem and are counted as an EXZ event. Not all equipment can detect and report EXZ events.

Line code violation (LCV; occasionally CV-L)

Both BPVs and EXZs are line code problems. For reporting purposes, they are combined for a total number of line code violations.

Path code violation (PCV; also CV-P)

Path coding is an error in the logical path from end to end. For ESF-framed links, it is a count of the CRC errors. SF-framed links have no check for correct transmission along a path, so the number of framing bit errors is used as a proxy.

Controlled slip (CS)

A controlled slip is the deletion or duplication of a DS1 frame, as described in Chapter 5. Although controlled slips may cause problems with the higher-level data stream, they do not cause any physical layer issues. In particular, the framing bits are maintained, so no out ...