S/UNI®-8x155 ASSP Telecom Standard Product Data Sheet
Released
The HCS is a CRC-8 calculation over the first 4 octets of the ATM cell header. The RXCP
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2
block verifies the received HCS using the polynomial, x + x + x + 1. The coset polynomial,
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4
2
x + x + x + 1, is added (modulo 2) to the received HCS octet before comparison with the
calculated result.
10.6.4 Performance Monitor
The Performance Monitor consists of 8-bit saturating HCS error event counter and a 24-bit
saturating receive cell counter. The error counter accumulates HCS errors. The 24-bit receive
cell counter counts all cells written into the receive FIFO. Filtered cells are not counted.
Each counter may be read through the microprocessor interface. Circuitry is provided to latch
these counters so that their values can be read while simultaneously resetting the internal
counters to 0 or 1, if appropriate, so that a new period of accumulation can begin without loss of
any events. It is intended that the counter be polled at least once per second so as not to miss
any counted events.
10.7 Receive POS Frame Processor (RXFP)
The Receive POS Frame Processor (RXFP) performs packet extraction, provides FCS error
correction, performs packet payload descrambling, and provides performance-monitoring
functions.
10.7.1 Overhead Removal
The overhead removal consists of stripping SONET/SDH overhead bytes from the data stream.
Once overhead bytes are removed, the data stream consists of POS frame octets that can be fed
directly to the descrambler or the POS Frame Delineation block.
10.7.2 Descrambler
When enabled, the self-synchronous descrambler operates on the POS Frame data,
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descrambling the data with the polynomial x + 1. Descrambling is performed on the raw data
stream, before any POS frame delineation or byte destuffing is performed. Data scrambling can
provide for a more robust system preventing the injection of hostile patterns into the data
stream.
10.7.3 POS Frame Delineation
This block accepts data one byte at a time and arranges it as POS framed octets. Frame
boundaries are found by searching for the Flag Character (0x7E). Flags are also used to fill
inter-packet spacing. This block removes the Flag Sequence and passes the data onto the Byte
Destuffing block.
The POS Frame Delineation is performed on the descrambled data and consists of arranging the
POS framed octets. Frame boundaries are found by searching for the Flag Character (0x7E).
Flags are also used to fill inter-packet spacing. This block removes the Flag Sequence and
passes the data onto the Byte Destuffing block. The POS Frame format is shown on Figure 6.
Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC- 2010299, Issue 2
77
PMC [ PMC-SIERRA, INC ]
