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Slajd 61
Status field
Used in LSSU,
Identified by a length indicator value
equal to 1 or 2 (when LI=1, the status
field consists of 1 octet, etc.)
Slajd 62
Check bits
Error detection is done by means of 16 check
bits provided at each signal unit
» the reminder after multiplication by x 16
and then division (modulo 2) by the generator
16 12 5
polynomial x + x + x + 1
of the content of the signal unit existing between,
but not including, the final bit of the opening flag
and the first bit of the check, excluding bits
inserted for transparency.
Slajd 63
„Zero” insertion and deletion
The flag code should not to be imitated by any other
part of the signal unit. To ensure it, the transmitting
signalling link terminal inserts a “0” after every
sequence of five consecutive 1s before the flags are
attached and the signal unit is transmitted,
At the receiving end, after flag detection and removal,
each „0” which directly follows a sequence of five
consecutive 1s is deleted,
„bit stuffing”.