SONET Port Configuration 2-83Bridging
A state of no transitions that lasts between 2.3 µs and 100 µs is declared an LOS
defect. The LOS defect is cleared after a 125 µs interval (the time required to
transmit one frame on a SONET network) during which no LOS defect is
detected.
If the LOS defect persists for a period of 2 to 3 seconds, an LOS failure will be
declared, an alarm indicator will be set, and an alarm message will be sent to
an Operations Systems application (responsible for overseeing the entire
network). The LOS failure is cleared when the LOS defect is absent for a period
of 9.5 to 10.5 seconds.
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 FrameÑSONET 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.