Datasheet

40G Cabling Technical Q&A Document
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Q. What is the specification for the MTP-LC cable?
A. According to the IEEE 40GBASE-SR4 specifications, the 40G signal is carried over a single
MTP-12 fiber, with only 8 of the 12 fibers used, where the remaining four are not used, and can
optionally be not present in the cable (to save cost). The specific mapping of Tx and Rx ports to
fiber strands is defined in the standard, with 1-4, and 9-12 used as shown below. This would be an
MTP-12 to an MTP-12.
Fiber Number
12
11
10
9
8 – 5
4
3
2
1
Transmit Channels:
1
2
3
4
Blank
Receive Channels:
Blank
4
3
2
1
To specify a cable that converts a 40G interface to 4 x 10G pairs the MTP-12 fibers are mapped
according to the 40G-SR4 specifications, identifying that Tx1 and Rx1 are mapped as Pair-1, Tx2
and Rx2 as Pair 2, and continue for all 4 pairs.
There are two different options for the cable to split MTP into LC - a straight through, or a
crossover, to support different connections needs.
To make sure that Tx is wired to Rx on the other end (a cross-over cable) the table below shows
both the MTP strand color and position number, the LC leg / side and color.
MTP Strand Color
MTP Position #
LC Leg / Side
LC Strand Color
Blue
1
1/B
Blue
Orange
2
2/B
Orange
Green
3
3/B
Green
Brown
4
4/B
Brown
Slate
5
NA
Slate
White
6
NA
White
Red
7
NA
Red
Black
8
NA
Black
Yellow
9
4/A
Yellow
Violet
10
3/A
Violet
Rose
11
2/A
Rose
Aqua
12
1/A
Aqua
If a “straight through” cable is required (as a X-over is already present in the path), then the above
table should be modified, such that 1<->1A, 12<->1B and so on, etc.