With the popularity of 40G QSFP+ modules in datacom industry, there are more alternatives for choose to replace the traditional 40GBASE-SR4 QSFP+ modules for multimode applications. To choose the most proper 40G QSFP+ modules for your applications not only offers the high performance but also saves more cost in the project.
Types of 40G Multimode QSFP+ Modules
Currently, there are three kinds of multimode 40G QSFP+ modules available in the market. They are:
| Type | Wavelength | Distance | Connector Type |
| 40GBASE-SR4 QSFP+ | 850 nm | 150 m (OM4) 100 m (OM3) |
MTP/MPO |
| 40GBASE-CSR4 QSFP+ | 850 nm | 400 m (OM4) 300 m (OM3) |
MTP/MPO |
| 40GBASE-SR Bi-Directional QSFP+ | 832 nm – 918 nm, BiDi | 150 m (OM4)100 m (OM3)30 m (OM2) | LC |
So, which one is the best for you? In the following sections, several factors should be considered.
Distance Consideration
The maximum transfer distance of QSFP+ modules refers to how long distance can the module support to transmit. It usually depends on the transmission distance that your project is required. In general, 40GBASE-SR4 QSFP+ module can support up to 100 meters over OM3 multimode fiber and 150 meters over OM4 multimode fiber. In other word, if your expected transmission distance is under 150 meters, you can choose 40GBASE-SR4 QSFP+ module with OM4 fiber cable. If you have a longer distance requirement, the 40GBASE-CSR4 will be better for you since it can support up to 400 meters over OM4 multimode fiber.
Cabling Consideration
Generally, current multi-mode optics standards for 40GbE use parallel technology, namely using multiple 10Gbps lasers, simultaneously transmitting across multiple fiber strands to achieve high data rates (4 x 10 Gbps). Because of this, 40G optics use MPO or MTP cabling instead of the traditional duplex LC cabling. The most commonly used MPO/MTP cable presents 12 separate strands of multi-mode fiber in a single ribbon cable. 40G multimode QSFP+ modules with MPO/MTP interface include 40GBASE-SR4 and 40GBASE-CSR4. However, if you deploy the 40 GbE over the existing 10GbE infrastructure, the former two kinds of 40G modules are not applicable. In this case, you may choose the 40G BiDi QSFP+ module which can support up to 150 meters over OM4 multimode duplex LC cabling.
Other Considerations
In addition to distance and cabling considerations, other considerations such as compatibility, receiver sensibility, temperature and so on are also important. Users should have a proper plan of the network and choose the proper parameters depending on the requirements.
Conclusion
40G QSFP+ modules are key components for 40GbE deployment. To choose the proper and cheap 40G QSFP+ can benefit the whole project. I will recommend you to visit FS.COM. They have a wide range options of 40G QSFP+ modules with very affordable prices. They may be an ideal choice for you.
