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23 Mar 2016

With the deployment of 40G systems in the data center, a lot of confusion occurred like: can the switches support such a high speed Ethernet? Can the optical transceivers be compatible with the switches? Which kind of optical transceiver is more cost-efficient? In order to solve these questions, the first and foremost thing is to know the most appropriate kind of fiber optic patch cable for the 40G QSFP+ transceiver (Quad Small Form-factor Pluggable transceiver) in the 40G connections.

As we all know, to accomplish the connections between these switches, fiber optic patch cord is usually linked to fiber optic transceivers which are plugged in Ethernet switches (as shown in the following picture). The quality of these connections has great effect on the reliability and stability of the whole system. Thus choosing the right type of fiber patch cables for 40G network becomes a big issue in 40G migration. Several important factors should be taken into consideration when selecting patch cords for 40G QSFP+ transceivers, namely the cable type, connector type and switch port.

switch connection
Cable Type

The performance of the optical signal differs when using different type of cables. Because different types of fiber cables can achieve different transmission distances. Therefore, the selection of the cable type is very important.

Very often, we can hear people ask: can a 40GBASE universal QSFP+ transceiver working on wavelength of 850nm be used with OM1 patch cords? The answer is yes, but not suggested. Why? As the optical signal transmission distance gets shorter as the data rate increases. The transmission distance would be limited by using OM1 optical cable with 40G QSFP+ transceiver. OM1 cable is only suggested for 100 Mb/s and 1000Mb/s transmission. Two upgraded cables—OM3 and OM4 are suggested for 40G QSFP+ transceivers in short distance.

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 former is suggested for 40G transmission over single-mode fiber in long distance up to 10km. The latter 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 patch cords should depend on the interface of 40G QSFP+ transceiver. MTP and LC are the most common types of interface on 40G QSFP+ transceiver. Usually 40G QSFP+ transceiver with MPO interface is designed for short distance transmission and LC for long 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 patch cords 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, for multi-fiber connection, polarity should be considered for the selection of the patch cord.

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 to the applications. So the right choice of patch cords for 40G QSFP+ transceiver can increase the network flexibility largely and effectively. Here are two most common examples in 40G applications. One is 40G QSFP+ to 40G QSFP+ cabling, the other 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.

It's very common that 40G ports need 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.

Conclusion

Cable type, connector type and switch port need to be considered comprehensively when choosing the right patch cords for 40G QSFP+ transceivers. They are closely related to the transmission distance, network flexibility and reliability of the whole 40G network. But in practical cabling for 40G QSFP+ transceivers, these three factors are far from enough. Planning and designing takes a lot of time and may not achieve ideal results as expected. However, FS.COM can solve your problems with professional one-stop service including the cost-effective solutions and high-quality products.

Originally published at http://www.fs.com/blog/fiber-patch-cable-selection-guide-for-40g-qsfp-transceivers.html



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