PM7344 datasheet(72/293 Pages) PMC

72 / 293 page

PM7344 S/UNI-MPH

DATA SHEET

PMC-950449

ISSUE 6

MULTI-PHY USER NETWORK INTERFACE

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

Figure 15

- Cell delineation State Diagram

HUNT

PRESYNC

SYNC

correct HCS

(bit by bit)

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

method. 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

as recommended in ITU-T Recommendation I.432.

Loss of cell delineation (LCD) is detected by counting the number of incorrect

cells while in the HUNT state. The counter value is stored in the RXCP LCD

Count Threshold register. The threshold has a default value of 360 which results

in an E1 format detection time of 77 ms, and a T1 format detection time of 100

ms.

The RXCP descrambles the cell payload field using the self synchronizing

descrambler with a polynomial of x43 + 1. The cell header is not descrambled.

Note that cell payload scrambling is optional in the S/UNI-MPH.

The HCS is a CRC-8 calculation over the first 4 octets of the ATM cell header.

The RXCP verifies the received HCS using the accumulation polynomial, x8 + x2

+ x + 1. The coset polynomial x6 + x4 + x2 + 1 is added (modulo 2) to the

received HCS octet before comparison with the calculated result as required by

the ATM Forum UNI specification, and ITU-T Recommendation I.432.

The RXCP can be programmed to drop all cells containing an HCS error or to

filter cells based on the HCS and/or the 4 octet cell header. Filtering according

to a particular HCS and/or 4 octet header pattern is programmable through the

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