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T1: A Survival Guide by Matthew Gast

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Performance Data

In addition to errors, monitoring performance data allows administrators to spot line degradations before they turn into stressful line-down situations. Most performance data is reported as the number of seconds for which a particular condition occurred. Here is a list of problems you might encounter, which are summarized in Table C-5:

Line errored seconds (LES; also ES-L)

Line errors include BPVs, EXZs, and LOS defects. The number of seconds with at least one of any of those errors is a line errored second.

Controlled slip seconds (CSS)

A controlled slip second is a second during which at least one controlled slip occurred. Controlled slips can be accurately measured only by CSU/DSUs.

Errored seconds (ES)

As defined for the path (as opposed to the line), an errored second is a second with at least one error off the following smorgasbord:

  • Path code violations

  • Controlled slips

  • Out of frame signals (severely errored framing defects)

  • AIS

An errored second for the path may also be abbreviated as ES-P. Early drafts of T1.231 that were used as the basis for the SNMP monitoring of T1 links used a different definition, which is discussed in Appendix D.

Errored second type B (ESB)

An errored second type B is a parameter that measures data corruption. It is a 1-second interval with between 2 and 319 CRC errors, but without severely errored framing problems or AIS. Because framing is functional and AIS is not present, the path appears to be functional.

Severely ...

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