Nortel Meridian 1 Option 11C Manual page 91

Figure 11
Bipolar violations
Normal
Error
Frame Bit Errors
The NTAK79/NTBK50 PRI CEPT PCM-30 stream is structured into a frame
of 32 8-bit timeslots. To maintain alignment of this frame structure, alternate
timeslot zeros have a specific frame alignment pattern (X0011011).
A frame bit error is acknowledged when any of the bits in the received pattern
are in error. This error rate provides an indication of the integrity of the
complete end-to-end span.
CRC-4 Word Errors
When operating in the CRC-4 multiframe format (CRC), frames are bundled
into groups of 16. This format includes a specific multiframe alignment
pattern in bit 0 of every even frame's timeslot 0 (001011XX).
Each odd frame timeslot 0 includes a CRC-4 cyclic redundancy checksum of
the previous 8 frames (sub-multiframe). This transmitted checksum is
compared against a calculated checksum at the receiver. If the two checksums
do not match, a CRC-4 Word error is indicated.
Group I error rates are processed on the PRI card based on software
downloadable parameters N1 and N2 (for each BPV, CRC and FBER). The
values for N1 are scaled on the card as follows:
PRI Maintenance
Error
Option 11C
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