Figure 3: Bipolar violations
Cyclic redundancy check (CRC)
The Extended Superframe Format (ESF) contains a checksum of all the data in the frame.
The
receiving side uses the checksum to verify the data.
The primary difference between BPV and CRC is that bipolar violation tracking indicates errors
on the local span, while CRC indicates errors on an end-to-end span. For example, on a
satellite link, BPV only detects errors in the span between the system and the satellite
connection. Since CRC traverses the entire span, it indicates an end-to-end bit error rate.
The CRC error counter is displayed with the LCNT L command in LD 60 provided that loop L
has been defined with ESF as a framing format. The framing format (D2, D3, D4, or ESF) is
selected in LD 17 when the loop is configured.
Bit error rate thresholds
There are three bit error rate thresholds set in LD 73. When a threshold is reached, a DTA
message is output. See Figure 4: BIPV and BIPC thresholds on page
48.
DTA011: Bit error rate maintenance threshold.
DTA012: Bit error rate out-of-service limit.
DTA013: Too many bit error rate out-of-service occurrences in 24 hours.
PRI error detection
ISDN Primary Rate Interface Maintenance November 2011 47
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