2.0 Mb Pri Error Detection - Nortel Meridian 1 Option 11C Manual

Page 90 of 126 PRI Maintenance

2.0 Mb PRI error detection

553-3011-315 Standard 13.00
• DIS SERV N: turns off the support of service and service acknowledge
messages for DCH link N.
• STAT SERV (N): displays the current service and service acknowledge
message SERV setting for individual DDCH N or for DCHIs.
Two new statuses are added for maintenance messages, FE MbSY = Far end
maintenance and FE DSBL = Far end disabled.
The Primary Rate Interface categorizes errors and alarm conditions into two
main groups, Group I and Group 2 errors.
Group I Errors
These are real-time calculated error-rate thresholds. Group I errors can
include:
• Bipolar Violations (BPV)
• Frame Bit Errors (FBER)
• CRC-4 Word Errors (CRC)
• Controlled Frame Slips
Bipolar Violations
In a alternate mark inversion (AMI) bipolar pulse stream, pulses alternate in
polarity. A bipolar violation has occurred when two pulses of the same
polarity are received in succession, as shown in Figure 11. This might be
caused by an electrical disturbance such as noise, a low signal level or a faulty
repeater Bipolar violations give a good indication of the integrity of the local
span from the Meridian 1 to the first repeater.
The PRI card, following the CEPT PCM-30, uses a zero code suppression
technique known as HDB3 which introduces intentional bipolar violations
onto the carrier. This is accounted for by the receiver and disregarded as
bipolar violation errors.
January 2002