PM5347 datasheet(69/302 Pages) PMC

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PM5347 S/UNI-PLUS

DATA SHEET

PMC-941033

ISSUE 6

SATURN USER NETWORK INTERFACE PLUS

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

provides a four cell deep receive FIFO. This FIFO is used to separate the

STS-3c/1 (STM-1) line timing from the higher layer ATM system timing.

Cell Delineation

Cell Delineation is the process of framing to ATM cell boundaries using the

header check sequence (HCS) field found in the cell header. The HCS is a

CRC-8 calculation over the first 4 octets of the ATM cell header. When

performing delineation, correct HCS calculations are assumed to indicate cell

boundaries. Cells are assumed to be byte-aligned to the synchronous payload

envelope. The cell delineation algorithm searches the 53 possible cell boundary

candidates individually to determine the valid cell boundary location. While

searching for the cell boundary location, the cell delineation circuit is in the

HUNT state. When a correct HCS is found, the cell delineation state machine

locks on the particular cell boundary, corresponding to the correct HCS, and

enters the PRESYNC state. The PRESYNC state validates the cell boundary

location. If the cell boundary is invalid, an incorrect HCS will be received within

the next DELTA cells, at which time a transition back to the HUNT state is

executed. If no HCS errors are detected in this PRESYNC period, the SYNC

state is entered. While in the SYNC state, synchronization is maintained until

ALPHA consecutive incorrect HCS patterns are detected. In such an event a

transition is made back to the HUNT state. The state diagram of the delineation

process is shown in Figure 5.

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