There are various 40G QSFP+ fiber optic module types. When choosing a QSFP+ 40G fiber optic module, you may find that these 40G fiber optic modules look very similar. For example, the letters and numbers of the 40GBASE-SR4 and 40GBASE-CSR4 modules are very similar. How can you distinguish them? You will find answer in below article.
What is 40GBASE-SR4?
40GBASE-SR4, also called QSFP-40G-SR4, is used for 40G Ethernet short-distance transmission. “SR” stands for short distance. The QSFP+ SR4 fiber optic module conforms to the IEEE 802.3ba 40GBASE-SR4 standard, uses MPO/MTP fiber optic connectors, and can transmit up to 100m when used with OM3 fiber and up to 150m when used with OM4 fiber.
The QSFP-40G-SR4 fiber optic module has independent transmit and receive sections, each with 4 parallel optical fibers. When the SR4 fiber optic module is used for a 40G connection, all 8 optical fibers are required, along with fiber optic patch cords with MPO 12 fiber optic connectors. Therefore, as shown in the diagram, 4 fibers in each link will be idle.
What is 40GBASE-LR4?
40GBASE-LR4, also known as QSFP-40G-LR4, is used for 40G Ethernet transmission, similar to 40GBASE-SR4. The QSFP+ LR4 optics conform to the IEEE 802.3ba 40GBASE-LR4 standard, use LC-duplex connectors, and can transmit over long distances (LR) of up to 10 kilometers on single-mode fiber. The QSFP-40G-LR4 fiber optic module uses the same package as the 40GBASE-SR4 and provides four independent transmit/receive channels, each with a bandwidth of 10Gbps.
To transmit 4 channels of signals over single-mode fiber, the 40G LR4 fiber optic module must multiplex or demultiplex the optical signals using an internal MUX/DEMUX. The operating mode of 40GBASE-LR4 is shown in the figure below.
What is 40GBASE-CSR4?
40GBASE-CSR4, also known as QSFP-40G-CSR4, is based on the IEEE 802.3ba 40GBASE-SR4 standard and is an extended version of 40GBASE-SR4, operating on the same principle. Furthermore, each 10G channel of the 40GBASE-CSR4 module conforms to the IEEE 10GBASE-SR specification, uses MTP/MPO interfaces, and can reach a maximum distance of 300m with OM3 fiber and 400m with OM4 fiber.
What is 40GBASE-CR4?
40GBASE-CR4, also known as QSFP-40G-CR4, is significantly different from the 3 types of 40G modules mentioned above. It is a pre-terminated copper cable with QSFP+ interfaces at both ends, what we called 40G QSFP+ direct-connect cable (DAC cable). While 40GBASE-SR4/LR4/CSR4 are fiber optic modules. Due to limitations in copper wire performance, the transmission distance of a passive 40G QSFP+ DAC cable can only reach 7m, while that of an active 40G QSFP+ DAC can only reach 10m.
How to Choose Between 40GBASE-SR4,40GBASE-LR4, 40GBASE-CSR4, and 40GBASE-CR4?
40GBASE-SR4, LR4, CSR4, and CR4 are all designed for 40G Ethernet transmission. The choice of which fiber optic module to use depends on the specific application. The table below lists the main differences between these four QSFP+ fiber optic modules and cables for your reference.
| Parameters | QSFP-40G-SR4 | QSFP-40G-LR4 | QSFP-40G-CSR4 | QSFP-40G-CR4 |
| Light source | VCSEL | DFP CWDM | VCSEL | / |
| Wavelength | 850nm | 1310nm | 850nm | / |
| Cable type | MMF | SMF | MMF | MMF |
| Connector | MTP/MPO | LC duplex connector | MTP/MPO | QSFP+ to 4 SFP+ / LC duplex connector |
| Maximum distance | 300m (OM3)400m (OM4) | 10km | 300m (OM3)400m (OM4) | 7m(passive);10m (active) |
FAQ
What are the differences between 40GBASE-SR4, iSR4, and eiSR4?
40GBASE-iSR4 (QSFP-40G-iSR4) is the product name for Huawei’s 40GBASE-SR4 fiber optic module, while 40GBASE-eiSR4 (QSFP-40G-eiSR4) refers to Huawei’s 40GBASE-CSR4 fiber optic module. In fact, the characteristics of 40GBASE-iSR4 and 40GBASE-eiSR4 are the same as those of 40GBASE-SR4 and 40GBASE-CSR4.
What are the differences between QSFP-40G-LR4 and QSFP-40G-PLR4?
QSFP-40G-PLR4 is also known in the industry as QSFP-40G-LR4 PSM. The main difference between 40GBASE-LR4 and 40GBASE-PLR4 lies in their interfaces and supported protocols. The 40GBASE-PLR4 module is based on the IEEE 802.3ae 10GBASE-LR standard and uses an MTP/MPO connector, while the 40GBASE-LR4 module is based on the IEEE 802.3ba 40GBASE-LR4 standard and uses an LC duplex connector.
What are the differences between 40GBASE-SR4 and AOC?
The 40G AOC active optical cable, like the 40GBASE-SR4 fiber optic module, is used for 40G short-distance applications. The difference is that QSFP+ AOC is a pre-terminated optical cable. One end connects to 40GBASE-QSFP+, and the other end can connect to SFP+ connectors, LC connectors, etc., in addition to QSFP+ connectors. The transmission distance of 40G AOC is generally no more than 100m.
