Agilent Technologies HDMP-3001 manual FCS Polynomial for Laps Processing, Laps Scrambling

packet. When this occurs an interrupt is generated. The packet can be ended via generation of an FCS error, via an abort sequence, or via “fill” bytes inserted in the gap, depending upon a software configurable escape code.

•Maintains performance monitor counters.

3.8.1.1FCS Polynomial for LAPS Processing

The HDMP-3001 supports CRC-32 Frame Check Sequence (FCS) generation and checking. The polynomial used to generate and

check the FCS is

X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 + X8 + X7 + X5 + X4 + X2 + X + 1.

The FCS field is calculated over all bits of the Address, Control, Payload, Information and Padding fields, not including any octets inserted for transparency. This does not include the Flag Se- quences nor the FCS field itself.

The CRC generator and checker are initialized to all ones. Upon completion of the FCS calculation the FCS value is ones-comple- mented. It is this new value that is inserted in the FCS field.

3.8.1.2LAPS Scrambling

Scrambling is performed to pro- tect the SONET/SDH line against malicious users deliberately send- ing packets to cause long run-lengths of ones or zeros or replicating the SONET/SDH fram- ing bytes. In the transmit direction an X43 +1 scrambler scrambles all SPE payload data. In the receive direction, a self-syn- chronous X43 +1 descrambler recovers the scrambled data.

3.8.2 GFP Processing

The Transmit GFP Processor pro- vides the insertion of packet- based information into the STS SPE. It provides packet encapsu- lation, FCS field generation, inter-packet fill and scrambling. The GFP Processor performs the following functions:

•Counts the Ethernet frame length.

•Calculates the payload length field, (PLI).

•Performs XOR with values as shown in Figure 11.

•Generates and sends cHEC and XOR (Figure 11).

•Sends programmable TYPE values.

•Generates and sends tHEC.

•Sends programmable DP, SP, and SPARE.

•Generates and sends eHEC.

•Generates and sends optional FCS.

3.8.2.1FCS Polynomial for GFP Processing

The HDMP-3001 supports CRC-32 Frame Check Sequence (FCS) generation and checking. The polynomial used to generate and

check the FCS is

X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 + X8 + X7 + X5 + X4 + X2 + X + 1.

The FCS field is calculated over the GFP payload, excluding all headers. The CRC generator and checker are initialized to all ones. Upon completion of the FCS cal- culation the FCS value is ones-complemented. It is this new value that is inserted in the FCS field.

3.8.2.2HEC Polynomial for GFP Processing

The following polynomial is used for generating and checking the

HECs:

X16 + X12 + X5 + 1

An HEC is calculated over each header. The initial value of the CRC registers is zero and the HEC is not inverted before being sent.

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