Wednesday 31 January, 2018 | RSS Feed

Fiber Patch Cable Selection Guide for 40G QSFP+ Transceivers

by www.fiber-mart.com

Numerous things need to be planned and designed for 40G migration. Whether the switches can support such a high speed Ethernet? Which kind of optical transceiver work best on the switches? Which optical transceiver is more cost-saving? Although most servers provided today can support 40G and 40G QSFP+ transceiver (Quad Small Form-factor Pluggable transceiver) are considered to be the most economic and effective transceivers for 40G migration, new problem still arises.
Patch Cords Matters to 40G
No matter how advanced the switches are, they all need to be connected together to form the whole 40G transmission network. To accomplish the connections between these switches, patch cords are usually linked to fiber optic transceivers which are plugged in Ethernet switches (as shown in the following picture). The quality of these connections can largely affect the reliability and stability of the whole 40G network. However, connectivity of 40G is much more complex than ever. Thus selecting the proper fiber patch cables for 40G network is more difficult and becomes a big issue in 40G migration. As mentioned, QSFP+ transceivers are suggested for 40G, this article will provide as detailed as possible about fiber patch cable selection for 40G QSFP+ transceivers.
Selecting Patch Cords for 40G QSFP+ Transceivers
Patch cords selection 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 patch cords for 40G QSFP+ transceivers, which are cable type, connector type and switch port.
Cable Type
Performances of optical signals with different wavelengths are often quite different. Even optical signals with the same wavelength perform totally different when they run through different fiber optic cables. Thus, the selection of the cable type is essential.
A typical question our customer asked when buying a fiber optical patch cords for 40G QSFP+ transceiver can illustrate this point clearly. 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 and quality 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 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 patch cords 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.
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. Here provide another article named “Understanding Polarity in MPO System” specifically explained MTP patch cords polarity for your reference.
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 patch cords 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 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.
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.
Cable type, connector type and switch port in selecting the right patch cords for 40G QSFP+ transceivers are necessary and important. 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 results good enough. However, fiber-mart can solve your problems with professional one-stop service including the cost-effective and reliable network designing and 40G products.

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