Reference Manual

Transmission Interface Handling G.703 2048 kbit/s
Severely Errored Seconds supervision
An SES is a second with at least one of the events:
•
CRC-4 is OFF: At least N4 frame bit errors
• CRC-4 is ON: At least N1 CRC-4 errors
• LOF alignment
• LOS
• AIS
• A-bit equal to “1” from the remote end
• N1 E-bit indication received from the remote end (only valid
when CRC-4 is used)
Two counters for severely errored seconds exist. Both are derived from
the downstream PCM port, but one is closely connected to downstream
faults while the other one is related to upstream faults.
The downstream counter is incremented by 1 for each second with at
least one of the following events:
• N1 CRC-4 errors (only valid when CRC-4 is used) or
•
N4 frame bit errors (only valid when CRC-4 is not used) or
•
1 LOF or
•
1 LOS or
• 1 AIS
The upstream counter is incremented by 1 for each second with at least
one of the following events:
• 1 A-bit=”1” or
• N1 E-bit=”0” (only valid when CRC-4 is used)
SES are not counted during unavailable state.
Both SES counters are reported after each BI.
UAS and Unavailable State supervision
UAS is a count of one-second intervals during which service is
unavailable. This period of time is referred to as the unavailable state.
The two directions (upstream and downstream) are supervised
separately. That is, one of the directions can be in the unavailable state
but the other is in the available state.
The counting of ES and SES is stopped for both directions as soon as at
least one of the directions is in the unavailable state.
An unavailable state for one direction is declared at the onset of P
consecutive SES for the direction of interest. These P seconds are
considered to be part of the unavailable time. A new period of available
state begins at the onset of Q consecutive seconds with no SES detected.
These Q seconds are considered to be part of the available time.
EN/LZT 720 0008 P2A
2001-11-28
419 (485)
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Preliminary