Transmission Interface Handling DS1 1544 kbit/s
• DF (Disturbance Frequency)
• SF (Slip Frequency)
• ES (Errored Seconds)
• SES (Severely Errored Seconds)
• UAS (Unavailable Seconds)
Bit Fault Frequency supervision
The number of bit errors in the received 1544 kbit/s signal is used to
establish an error rate. The CRC-6 sequence is used to obtain the
number of bit errors. In this method, the distribution of errors in the
time is considered. Bursts of faults decrease the number of CRC errors
detected compared to what would have been detected with an equal
distribution of faults in time.
The probability of bit faults appearing in bursts is greater than the
probability of detecting single isolated bit faults. This probability
increases with the real bit error rate, and with the length of the time
period over which the real bit fault frequency is calculated.
In the used method, the number of CRC-6 errors is counted during the
base interval. Then, a translation to bit fault frequency is performed.
The bit fault frequency is supervised and reported as the mean bit error
ratio in ppm (parts per million) during the BI (Base Interval).
Disturbance Frequency supervision
This supervision monitors detected fault situations which are regarded
as disturbances upon detection. Upon detection the following events are
regarded as disturbances:
• LOF (Loss Of Frame) alignment
• LOS (Loss Of Signal)
• AIS (Alarm Indication Signal)
• RAI (Remote Alarm Indication) received from remote end
Two disturbance frequency counters 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 DF downstream counter is increased by 1 for each occurrence of
• LOF or
• LOS or
• AIS
The DF upstream counter is increased by 1 for each occurrence of RAI.
Every detected fault situation is registered and regarded as a disturbance,
even if it does not last long enough to be recognised as a fault.
The DF is supervised and reported as the number of disturbances during
the BI. Both counters are handled separately.
EN/LZT 123 2697 R5A
1998-08-13
207 (306)
© Ericsson Radio Systems AB
— All Rights Reserved —
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