How to Choose a QSFP+ transceiver?

40G Ethernet standard now is already a popular choice for the rapid growth of global regional and local fiber communication network. For 40G network applications, fiber optic transceivers of two different package forms are commonly used, which are QSFP+ transceiver (quad small form-factor pluggable plus transceiver) and CFP transceiver (C form-factor pluggable transceiver). QSFP+transceiver is more popular in 40G application. Today we are going to discuss how to choose the 40GBASE QSFP+ transceiver. When choosing, there are several factors that you need to take into cinsideration, such as the media system, the connector type, transmission distance, wavelength, etc. The following text will talk about these factors one by one.

Fiber Type

First, choose the right QSFP+ transceiver according to the transport media, namely the fiber type. According to the IEEE 802.3ba 40G Ethernet standard, there are three types of transceivers used respectively in three types of transport media: single mode fiber (SMF), multimode fiber (MMF) and copper.

• SMF: 40GBASE-LR4 QSFP+ transceiver reaches 40 Gb/s Ethernet over four wavelengths carried by a singlemode fiber optic cable.
• MMF: 40GBASE-SR4 QSFP+ transceiver reaches 40 Gb/s Ethernet over four short-range multimode fiber optic cables.
• Copper: 40GBASE-CR4 QSFP+ transceiver reaches 40 Gb/s Ethernet over four short-range twinaxial copper cables bundled as a single cable over a standard pair of G.652 single-mode fiber.

Interface Type

Choose the right transceivers which are compliant with the proper connectors. The connectors widely-used mainly have following types: duplex LC connector and MPO connector (or MTP connector, a high-performance MPO connector). For instance, Cisco QSFP-40G-LR4 40GBASE-LR4 QSFP+ transceiver is compliant with the duplex LC connector, while Cisco QSFP-40G-SR4-S 40GBASE-SR4 QSFP+ transceiver and HP JG709A 40GBASE-CSR4 QSFP+ transceiver are compliant with the MPO connector. The picture belows shows duplex LC connector and MPO (MTP) connector.

Wavelength

The wavelength that QSFP+ transceivers operate on is another important factor in choosing the proper QSFP+ transceiver. For instance, QSFP-40G-LX4 QSFP+ transceiver converts 4 inputs channels (1271nm, 1291nm,1311nm, 1331nm) of 10Gb/s electrical data to 4 CWDM optical signals, and multiplexes them into a single channel for 40Gb/s optical transmission. While some other QSFP+ transceivers like QSFP-40GBD-SR QSFP+ transceiver consists of two 20-Gbps transmit and receive channels in the 832-918 nm wavelength range.

Transmission Distance

When choosing the most appropriate QSFP+ transceiver, you also need to consider the transmission distance and the reach requirements you need in reality. The most common types of QSFP+ transceiver divided by its transmission distance can reach up to 100m, 150m, 300m, 400m, 1km, 2km, 10km, 40km, etc. For example, 40GBASE-LR4 QSFP+ transceiver can reach up to 10km, suitable for long reach transmission; 40GBASE-LX4 QSFP+ transceiver is designed to supports link lengths of 100m and 150m respectively on laser-optimized OM3 and OM4 multimode fiber cables. And some others, like 40GBASE-ER4 QSFP+ transceiver which supports link lengths of up to 40km on single-mode fiber cable is designed to use in long distance transmission.

Cost

The total cost on QSFP+ transceivers is a large sum of money. Cost is one aspect that should be considered in 40G QSFP+ transceiver selection. To a limit buget, you have to figure out the best choice. Third party transceivers that are compatible with a variety types of switches can be found in today's market. They have the same performances that the original brand transceivers have, but cost less money. Selecting compatible QSFP+ transceivers has become the choice of many data centers, and it is necessary to select them from a company that assures 100% compatibility and interoperability.

Summary

Before choosing a QSFP+ transceiver, you must first find out what kind of QSFP+ transceiver you need. Whether you need singlemode fiber QSFP+ transceiver or multimode fiber QSFP+ transceiver, duplex LC connector or MPO connector, or you need it to transmit 100m or 10km, you should consider all the above-mentioned factors comprehensively. Only by doing so can you make the best selection for your network.