PMC-Sierra PM5349 manual Descrambler, Cell Filter and HCS Verification

Models: PM5349

1 252
Download 252 pages 6.23 Kb
Page 50
Image 50

PMC-Sierra, Inc.

S/UNI-QUAD

DATASHEET

PM5349 S/UNI-QUAD

PMC-971239

ISSUE 6

SATURN USER NETWORK INTERFACE (155-QUAD)

 

 

 

Figure 4: Cell Delineation State Diagram

correct HCS (byte by byte)

HUNT

Incorrect HCS (cell by cell)

PRESYNC

ALPHA

 

consecutive

 

incorrect HCS's

 

(cell by cell)

DELTA

SYNC

consecutive

 

correct 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.

10.6.2Descrambler

The self synchronous descrambler operates on the 48 byte cell payload only. The circuitry descrambles the information field using the x43 + 1 polynomial. The descrambler is disabled for the duration of the header and HCS fields and may optionally be disabled for the payload.

10.6.3Cell 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

Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use

44

Page 50
Image 50
PMC-Sierra PM5349 manual Descrambler, Cell Filter and HCS Verification