Pri Error Detection; Bit Error Rate - Nortel Communication Server 1000S Maintenance Manual

Page 58 of 210 Primary Rate Interface maintenance

PRI error detection

Bit error rate

Figure 3
Bipolar violations
Normal:
Error:
553-3001-517 Standard 2.00
Bit-error-rate monitoring detects errors in transmission. See Figure 3.
Bipolar violation (BPV) tracking
In a bipolar pulse stream, pulses alternate in polarity. A bipolar violation has
occurred if, after transmission, two pulses of the same polarity are received in
succession (this could be caused by an electrical disturbance such as noise).
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.
September 2004
553-1347