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PMC-Sierra, Inc.
PM5349 S/UNI-QUAD
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PMC-971239 ISSUE 6 SATURN USER NETWORK INTERFACE (155-QUAD)
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
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Figure 4: Cell Delineation State Diagram
HUNT
PRESYNC
SYNC
correct HCS
(byte by byte)
DELTA
consecutive
correct HCS's
(cell by cell)
Incorrect HCS
(cell by cell)
ALPHA
consecutive
incorrect HCS's
(cell by cell)
The values of ALPHA and DELTA determine the robustness of the delineation
process. ALPHA determines the robustness against false misalignments due to
bit errors. DELTA determines the robustness against false delineation in the
synchronization process. ALPHA is chosen to be 7 and DELTA is chosen to be 6.
These values result in an average time to delineation of 33.66 µs for the STS-3c
(STM-1) rate.
10.6.2
Descrambler
The self synchronous descrambler operates on the 48 byte cell payload only. The
circuitry descrambles the information field using the x
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+ 1 polynomial. The
descrambler is disabled for the duration of the header and HCS fields and may
optionally be disabled for the payload.
10.6.3
Cell Filter and HCS Verification
Cells are filtered (or dropped) based on HCS errors and/or a cell header pattern.
Cell filtering is optional and is enabled through the RXCP registers. Cells are
passed to the receive FIFO while the cell delineation state machine is in the
SYNC state as described above. When both filtering and HCS checking are