PM7346 datasheet(90/419 Pages) PMC

90 / 419 page

PM7346 S/UNI-QJET

DATASHEET

PMC-960835

ISSUE 6

SATURN QUAD USER NETWORK INTERFACE FOR J2, E3, T3

PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA INC., AND ITS CUSTOMERS’ INTERNAL USE 69

synchronization process. ALPHA is chosen to be 7 and DELTA is chosen to be 6

as recommended in ITU-T Recommendation I.432. These values result in a

maximum average time to frame of 127 µs for a DS3 stream carrying ATM cells

directly mapped into the DS3 information payload.

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-50 LCD

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

in a DS3 application detection time of 3.5 ms, an E3 G.832 application detection

time of 4.5 ms, and E3 G.751 application detection time of 5.0 ms, a J2

application time of 24.8ms, an E1 application detection time of 77 ms, and a DS1

application detection time of 100 ms. If the counter value is set to zero, the LCD

output signal is asserted for every incorrect cell.

9.9

RXCP-50 Receive Cell Processor

The Receive Cell Processor (RXCP-50) Block integrates circuitry to support

scrambled or unscrambled cell payloads, scrambled or unscrambled cell

headers, header check sequence (HCS) verification, idle cell filtering, and

performance monitoring.

The RXCP-50 operates upon a delineated cell stream. For PLCP based

transmissions systems, cell delineation is performed by the SPLR. For non-

PLCP based transmission systems, cell delineation is performed by the ATMF.

Framing status indications from these blocks ensure that cells are not written to

the RXFF while the SPLR is in the loss of frame state, or cells are not written to

the RXFF while the ATMF is in the HUNT or PRESYNC states.

The RXCP-50 descrambles the cell payload field using the self synchronizing

descrambler with a polynomial of x43 + 1. The header portion of the cells can

optionally be descrambled also. Note that cell payload scrambling is enabled by

default in the S/UNI-QJET as required by ITU-T Recommendation I.432, but may

be disabled to ensure backwards compatibility with older equipment.

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

The RXCP-50 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-50 can be programmed to drop all cells containing an HCS error or to

filter cells based on the HCS and the cell header. Filtering according to a

particular HCS and the GFC, PTI, and CLP bits of the ATM cell header (the VCI

and VPI bits must be all logic 0) is programmable through the RXCP-50 registers.

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