Note:
Bipolar 8 Zero Substitution (B8ZS) introduces intentional bipolar violations. The T1
equipment must treat them as such and disregard them. This explains why B8ZS can be
used only if all the equipment on the T1 span (end-to-end) supports it. Otherwise, the
intentional BPVs take the link down.
Figure 19: Bipolar violations
Cyclic Redundancy Check
The 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 cyclic redundancy check (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 detects errors only 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.
DTI/PRI hardware detects BPV or CRC errors. It sends an overflow (OVFL) message to the
system 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
Table 49: Bit error rate
messages on page
112.
Table 49: Bit error rate messages
Message Explanation
DTA011 Bit error rate maintenance threshold has been reached.
DTA012 Bit error rate out-of-service limit has been reached.
DTA013 Too many bit error rate out-of-service occurrences in the last
24 hours.
1.5 Mb DTI/PRI maintenance
112 ISDN Primary Rate Interface Maintenance November 2011
Comments? infodev@avaya.com
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