Nortel Meridian 1 Option 11C Manual page 64

Page 64 of 100 DTI/PRI Maintenance
553-3011-310 Standard 13.00
Cyclic Redundancy Check
The Extended Superframe Format (ESF) contains a checksum of all 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 in 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 Meridian 1 and the satellite connection. Since CRC
traverses the entire span, it indicates an end-to-end bit error rate.
DTI/PRI hardware detects BPV or CRC errors. It sends an overflow (OVFL)
message to the Meridian 1 CPU each time 1024 BPV or CRC errors are
detected. Running the midnight routines prints the number of overflows and
clears the counter.
Bit error rate threshold messages
There are three bit error rate thresholds set in LD 73, using one of two
prompts: BIPV or BIPC. When a threshold is reached, a DTA message is
produced. (See Figure 7.)
Message
DTA011
DTA012
DTA013
January 2002
Explanation
Bit error rate maintenance threshold has been
reached.
Bit error rate out of service limit has been
reached.
Too many bit error rate out of service
occurrences in the last 24 hours.