S/UNI®-JET Data Sheet
Released
Figure 5 Framing Algorithm (CRC_REFR = 1)
Reset
or
Else
Slip 1 bit
Out of Frame
Framing
Pattern
Matched
Mark multiframe alignment
Fail
Confirm Framing Pattern
in next multiframe
Pass
Fail
Fail
Fail
Check CRC-5 Sequence
Pass
Confirm Framing Pattern
in next multiframe
Pass
Check CRC-5 Sequence
Pass
Declare in-frame
Using this algorithm, the J2-FRMR will find frame in 10.22 ms, on average when starting the
-4
search in the worst possible position, given a 10 error rate and no static mimic patterns. The
algorithm will reject 99.90% of mimic patterns. Further protection against mimic patterns is
available by monitoring the rate of CRC-5 errors.
Once frame alignment is found, the block sets the LOF indication low, indicates a change of
frame alignment (if it occurred). The block declares LOF alignment if 7 consecutive FASs have
3
-
been received in error. In the presence of a random 10 bit error rate the frame loss criteria
provides a mean time to falsely lose frame alignment of 1.65 years. The Frame Find Block can be
forced to initiate a frame search at any time when the REFRAME bit in the J2-FRMR
configuration. Conversely, when the FLOCK bit is set to logic one, the J2-FRMR will never
declare LOF or search for a new frame alignment due to excess framing bit errors.
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990267, Issue 3
61
PMC [ PMC-SIERRA, INC ]
