PM5381-BI PMC-Sierra, Inc., PM5381-BI Datasheet - Page 92

• Manufacturer Part Number: PM5381-BI
• Description: ATM UNI, Single Channel ATM PHY Interface for 2488.32Mbps
• Manufacturer: PMC-Sierra, Inc.

10.7.4
10.7.5
10.7.6
10.7.7
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2000489, Issue 4
The HCS is a CRC-8 calculation over the first 4 octets of the ATM cell header. The RCFP block
verifies the received HCS using the polynomial, x
x
result.
ATM Performance Monitor
The Performance Monitor consists of an 8-bit saturating HCS error counter and a 32-bit
saturating receive cell counter. A 32-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.
POS 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 PPP/HDLC frame octets that can
be fed directly to the descrambler or the PPP/HDLC Frame Delineation block.
POS Descrambler
When enabled, the self-synchronous descrambler operates on the PPP Frame data, descrambling
the data with the polynomial x 43 +1. Descrambling is performed on the raw data stream, before
any PPP 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.
POS PPP/HDLC Frame Delineation
The PPP/HDLC Frame Delineation is performed on the descrambled data and consists of
arranging the 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 and Idle
Sequences and passes the data onto the Byte Destuffing block. The PPP/HDLC Frame format is
shown in the figure below.
Figure 14 PPP/HDLC Over SONET Frame Format
2
+ 1, is added (modulo 2) to the received HCS octet before comparison with the calculated
Flag
Packet (PPP or other)
POS Frame
8
S/UNI-2488 Telecom Standard Product Datasheet
+ x
2
+ x + 1. The coset polynomial, x
FCS
Flag
Flag
Released
6
+ x
4
92
+