Comparison of 40G QSFP+ LR4 and SR4 Optics

At present, for 40GbE, there are several kinds of transmission solutions. People usually use the 4 x 10 GE Breakout cable, 40G QSFP+ module or 40G CFP modules to achieve the 40GbE. Among them, the first two kinds of solutions are most widely used for nowaday 40 Gigabit Ethernet. For aggregation and core native 40 GbE, the 40G QSFP+ module is an ideal choice. There are many different variants of 40G QSFP+ modules which are defined by IEEE 802.3ba to support different applications. 40GBASE-LR4 (40G-QSFP-LR4) and 40GBASE-SR4 (40G-QSFP-SR4) QSFP+ optics are the most commonly used specifications of 40G QSFP+ optics. So, what are the differences between them on the module structure and applications?

The IEEE 802.3ba committee ratified the 40 Gigabit Ethernet standard in June, 2010. Along with the general specification, it defined a number of fiber optic interfaces. These standard interfaces attempted to satisfy a number of different objectives including support for multi-mode fiber and single-mode fiber compatibility. 40BASE-LR4 and 40BASE-SR4 QSFP+ optics both comply the IEEE 802.3ba and QSFP Multisource Agreement (MSA), but for different applications according to their features and parameters. Here are some detailed differences between 40BASE-LR4 and 40BASE-SR4 QSFP+ modules.

  • 40GBASE-LR4 QSFP+ transceivers are most commonly deployed between data-center or IXP sites with single mode fiber.
  • 40GBASE-SR4 QSFP+ transceivers are used in data centers to interconnect two Ethernet switches with 12 lane ribbon OM3/OM4 cables.
Fiber Type and Connector
  • 40GBASE-LR4 QSFP+ transceivers support link lengths of up to 10 kilometers over a standard pair of G.652 single-mode fiber with duplex LC connectors.
  • 40GBASE-SR4 QSFP+ transceivers are generally enable high-bandwidth 40G optical links over 12-fiber parallel fiber terminated with MPO/MTP multifiber connectors.
QSFP+ connectors
Wavelength (nm)
  • 40GBASE-LR4 QSFP+ (Multiplexing and demultiplexing of the four wavelengths are managed within the device): 1271 nm, 1291 nm, 1311 nm, 1331 nm
  • 40GBASE-SR4 QSFP+: 4 x 850 nm
Transmission Distance
    – 10 km on single-mode– 4λ x 10G 1300 nm region
  • 40GBASE-SR4 QSFP+ (parallel optics)
    – 100 m on OM3–10G on 4 fibers per direction
    – 150 m on OM4 –10G on 4 fibers per direction

Obviously, the 40G QSFP LR4 is designed for long transmission used with single-mode fiber while 40G QSFP SR4 is for short distance with OM3/OM4. And “4” here means four lanes. Additionally, they are in different wavelengths and with different connectors. When they used in actual network, they are used different technology.

Ok, the article will be end here as today’s topic is simple. I hope that this post will give you some help and of course due to the limited knowledge of the author, there are some inevitable errors and omissions existing in this paper. Futhermore, if you are very interested in this topic and want to gain more information about it, I suggest you to read the IEEE 802.3ba and QSFP Multisource Agreement (MSA).

QSFP+ Transceiver Recommendation

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