Upgrading the existing system to 40G network can be a tough and complicated task since there are considerable amount of factors to plan and design. Whether the switches are capable of supporting such a high speed Ethernet? What kind of optical transceiver works best on the switches? Which optical transceiver is more cost-efficient? 40G QSFP+ transceiver (Quad Small Form-factor Pluggable transceiver) are considered to be the most economical and effective transceiver solutions for 40G migration. The selection for fiber patch cords for interconnection is vital as well.
Patch Cords Matter to 40G
To successfully build 40G transmission network, the switches need to be connected together. In this case, patch cords are usually linked to fiber optic transceivers which are plugged in Ethernet switches (as shown in the following picture), thus to accomplish connections between these switches. 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 critical issue in 40G migration. It is known that QSFP+ transceivers are suggested for 40G, and this article will provide some detailed information 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 often vary from different wavelengths. 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 that frequently asked when buying fiber optic patch cords for 40G QSFP+ transceiver can illustrate this point clearly. Can a 40GBASE universal QSFP+ transceiver working on wavelength of 850 nm be used with OM1 patch cords? The answer is yes, but not suggested. As the optical signal transmission distance gets shorter as the data rate increases, the transmission distance and quality would be limited by using OM1 patch cords with 40G QSFP+ transceiver. OM1 cable is only suggested for 100Mb/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 40GBASE-LR4 is suggested for 40G transmission over single-mode fiber in long distance up to 10 km. Whereas the 40GBASE-SR4 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 economical solutions for 40G in short distance with lower insertion loss and higher bandwidth.
Connector Type
The connector type of the patch cords depends on the interface of 40G QSFP+ transceiver. Currently there are two interfaces commonly adopted by 40G QSFP+ transceiver, which are MPO 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 features 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-saving and stable solution for 40G QSFP+ transceivers. However, for multi-fiber connection, polarity should be considered for the selection of the patch cord.
However, to meet the market demands, 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
Network flexibility becomes more crucial as the speed of Ethernet increases. When it comes to 40G, network flexibility becomes an urgent issue which is closely related to applications. Right selection of patch cords for 40G QSFP+ transceiver can increase the network flexibility significantly and effectively. Here offer two most common examples in 40G applications: 40G QSFP+ to 40G QSFP+ cabling and 40G QSFP+ to SFP+ cabling.
For 40G QSFP+ to 40G QSFP+ cabling:
1. For distance up to 100 m, the 40GBASE-SR4 QSFP+ transceiver can be used with OM3 fiber patch cable attached with a MPO on each end.
2. For distance up to 150 m, the 40GBASE-SR4 QSFP+ transceiver can be used with OM4 fiber patch cable attached with a MPO on each end.
3. For distance up to 10 km, 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 are 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 the picture below).
Conclusion
Fiber optic patch cords hold an essential position in connecting and accomplishing the whole 40G transmission network. When selecting the right patch cable for 40G QSFP+ transceiver, cable type, connector type and switch port should be taken into consideration, since these three factors are closely relevant to transmission distance, network flexibility and reliability of the whole 40G network. What we discussed above simply offers you a reference guide. For professional and cost-effective network design as well as 40G products, please visit www.fs.com.
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