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Fiber Patch Cable Selection Guide for 40G QSFP+ Transceivers

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It is known to us that fiber patch cables are often used with fiber optic transceivers to accomplish connections between switches. And the quality of these connections can largely affect the reliability and stability of the whole 40G network. This applies in 40G transmission network as well. Fiber patch cable is a big issue to 40G not only because the switch connections necessity, but also because of the transmission principle of the fiber optic signals and the high density trend of 40G transmission. Several important factors should be taken into account when selecting fiber patch cables for 40G QSFP+ transceivers, which are cable type, connector type and switch port.

Cable Type

IEEE has announced standards for 40G transmission in both long distance and short distance, which are 40GBASE-SR4 and 40GBASE-LR4. (SR stands for short-reach and LR stands for long reach). The latter is suggested for 40G transmission over single-mode fiber in long distance up to 10km. The former is for 40G transmission in short distance over multimode fiber—OM3 (up to 100 meters) and OM4 (up to 150 meters). OM3 and OM4, which are usually aqua-colored, are accepted economic solutions for 40G in short distance with lower insertion loss and higher bandwidth.

Connector Type

The connector type of the fiber patch cables should depend on the interface of 40G QSFP+ transceiver. Currently there are two interfaces commonly adopted by 40G QSFP+ transceiver which are MTP and LC. Usually 40G QSFP+ transceiver with MPO interface is designed for short transmission distance and LC for long transmission distance. However, several 40G QSFP+ transceivers like 40GBASE-PLR4 and 40GBASE-PLRL4 have MPO interfaces to support long transmission distance.

QSFP4

High density is the most obvious characteristic of 40G transmission, which is largely reflected in the MTP connectors on fiber patch cables used with 40G QSFP+ transceiver. As QSFP+ transceiver uses four 10G channels to achieve the 40G transmission, thus 4 pairs of fibers are used and the 12-fiber MTP connectors can provide a time-save and stable solution for 40G QSFP+ transceivers.

However, to meet the market needs, 40G QSFP+ transceiver with LC interface is also available. This type of QSFP transceiver uses four lanes with each carrying 10G in 1310nm window multiplexed to achieve 40G transmission. For this type, patch cable with duplex LC connector should be used.

Switch Port

The importance of network flexibility gradually reveals as the speed of Ethernet increases. When it comes to 40G, network flexibility becomes an urgent issue which is closely related with applications. Right selection of fiber patch cables for 40G QSFP+ transceiver can increase the network flexibility largely and effectively. Here offer two most common examples in 40G applications. One is 40G QSFP+ to 40G QSFP+ cabling, the other one is 40G QSFP+ to SFP+ cabling.

For 40G QSFP+ to 40G QSFP+ cabling:
  • For distance up to 100m, the 40GBASE-SR4 QSFP+ transceiver can be used with OM3 fiber patch cable attached with a MPO one each end.
  • For distance up to 150m, the 40GBASE-SR4 QSFP+ transceiver can be used with OM4 fiber patch cable attached with a MPO one each end.
  • For distance up to 10km, the 40GBASE-LR4 QSFP+ transceiver can be used with single-mode fiber with LC connectors. The picture above shows the transmission of 40GBASE-LR4 QSFP+ transceiver with LC connector over single-mode fiber.

mtp-8lc-harness-cable-type-b

It’s very common that 40G ports is needed to be connected with 10G port. In this case, fan out patch cable with MTP connector on one end and four LC duplex connectors on the other end is suggested (as shown in picture below).

Conclusion

To select the right fiber patch cables for 40G QSFP+ transceivers, it is necessary and important to consider the cable type, connector type and switch port. They are closely related to the transmission distance, network flexibility and reliability of the whole 40G network.

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