PM5381-BI PMC-Sierra, Inc., PM5381-BI Datasheet - Page 91

• Manufacturer Part Number: PM5381-BI
• Description: ATM UNI, Single Channel ATM PHY Interface for 2488.32Mbps
• Manufacturer: PMC-Sierra, Inc.

10.7.2
10.7.3
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2000489, Issue 4
Figure 13 Cell Delineation State Diagram
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 2 ms for the
STS-48c (STM-16c) rate.
ATM Descrambler
The self-synchronous descrambler operates on the 48 byte cell payload only. The circuitry
descrambles the information field using the x 43 + 1 polynomial. The descrambler is disabled for
the duration of the header and HCS fields and may optionally be disabled for the payload.
ATM Cell Filter
Cells are filtered (or dropped) based on HCS errors and/or a cell header pattern. Cell filtering is
optional and is enabled through the RCFP 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 enabled, cells are dropped if HCS errors are detected, or if the header
contents match the pattern contained in the RCFP Idle Cell Header and Mask register. Idle cell
filtering is accomplished by writing the appropriate cell header pattern into the RCFP Idle Cell
Header and Mask Pattern register. Idle/Unassigned cells are assumed to contain the all zeros
pattern in the VCI and VPI fields. The RCFP Idle Cell Header and Mask register allows filtering
control over the contents of the GFC, PTI, and CLP fields of the header.
ALPHA
consecutive
incorrect HCS's
(cell by cell)
HUNT
correct HCS
(byte by byte)
SYNC
Incorrect HCS
(cell by cell)
S/UNI-2488 Telecom Standard Product Datasheet
PRESYNC
DELTA
consecutive
correct HCS's
(cell by cell)
Released
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