To implement 40G Ethernet network, 40GBASE fiber optic transceivers, a high-performance and flexible component, are developed and widely used. 40GBASE optical transceivers are mainly of two different package forms, which are CFP transceiver (C form-factor pluggable transceiver) and QSFP+ transceiver (quad small form-factor pluggable plus). QSFP+ transceiver is the more commonly used module type in 40G Ethernet networks. This post will mainly discuss how to choose a 40GBASE QSFP+ transceiver. 40GBASE QSFP+ transceivers are used to interface networking hardware to a fiber optic cable, the choice of them depends on many factors, like the media system, the connector type, transmission distance, wavelength, etc. Thus you should consider all these factors comprehensively before you choose them.

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.

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.

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.

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.

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.

To achieve a fast and successful selection of the 40G QSFP+ transceivers, 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 to transmit 100m or 10km, you should take all these factors into consideration. Thus you make the best selection for your network.

Posted by: jowang at 02:23 AM | No Comments | Add Comment
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