Filter
Top Products
23
3.8.1.1 FCS 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
X
32
+ X
26
+ X
23
+ X
22
+ X
16
+ X
12
+ X
11
+ X
10
+ X
8
+ X
7
+ X
5
+ X
4
+
X
2
+ 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.
3.8.1.2 LAPS 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 X
43
+1 scrambler
scrambles all SPE payload data.
In the receive direction, a self-syn-
chronous X
43
+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.
3.8.2.1 FCS 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
X
32
+ X
26
+ X
23
+ X
22
+ X
16
+ X
12
+ X
11
+ X
10
+ X
8
+ X
7
+ X
5
+ X
4
+
X
2
+ 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.
3.8.2.2 HEC Polynomial for GFP
Processing
The following polynomial is used
for generating and checking the
HECs:
X
16
+ X
12
+ X
5
+ 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.
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.