Cabletron Systems CSX400, CSX200 manual Loss of Frame, Errored Seconds

Bridging

A Loss of Signal may also be detected if the received signal level (e.g., the incoming optical power) falls below a Bit Error Rate (BER) threshold of 1 in 103. A BER is the number of coding violations detected in an interval of time (usually one second). A predicted BER of 1 in 103 means that during each second, there is an error ratio of 1 errored bit per 1,000 bits sent. This state clears when two consecutive framing patterns are received, and no Òall zerosÓ LOS conditions are detected in the intervening time (one frame).

Note that for path- or line-terminating SONET network elements, LOS failure detection is also linked to the declaration or clearing of Loss of Frame (LOF) failures (described below). If there was a previously existing LOF failure at the time an LOS failure is declared, the LOF failure will be cleared; if an existing LOS failure is cleared, but LOF failure conditions still exist, an LOF failure will be immediately declared on clearing the LOS failure.

Loss of Frame

SONET frames uses A1 and A2 framing bytes in the section overhead to indicate the beginning of the frame. An Out of Frame (OOF) alignment defect (also known as a Severely Errored FrameÑSEFÑdefect) occurs when four consecutive SONET frames are received with invalid patterns in these framing bytes. This defect is cleared when two consecutive SONET frames are received with valid framing patterns.

A Loss of Frame (LOF) defect occurs when this OOF/SEF defect persists for a period of 3 milliseconds. This defect is cleared when the incoming signal remains continuously in-frame for a period of 1 to 3 milliseconds.

An LOF failure is declared when an LOF defect persists for a period of 2 to 3 seconds (except when a Loss of Signal defect or failure is present, as described above). An LOF failure is cleared if an LOS failure is declared, or when the LOF defect is absent for 9.5 to 10.5 seconds.

Statistics

Statistics are given for both the Near-End and Far-End of the SONET/SDH path. Far-end statistics are taken from the far-end block error code (FEBE)Ñused to indicate that the remote entity at the far-end of the path has detected errored data Ñwithin the Path Overhead of SONET frames.

You can view statistics for the current 15-minute interval, or accumulated over the last one-, eight-, or 24-hour period by clicking on the appropriate selection button.

Errored Seconds

The counter associated with the number of Errored Seconds, or Far-End Errored Seconds, encountered by a SONET/SDH Path in the speciÞed interval.

An Errored Second (ES) is a second with one or more coding violations (bit parity errors) at the associated layer reported at the Section, Line, or Path layer of the SONET link, or a second during which at least one or more incoming defects (e.g., Loss of Signal, Loss of Pointer, or Loss of Frame) has occurred at that layer.

4-80 SONET Port Configuration