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40G Cabling and Transceivers: Q&A

Dec 10th 2015 at 10:31 PM

Q. What is the 40GbE max supported distances?
A. The IEEE 40GBASE-X standard describes the following:

  • 40GBASE-SR4 supports up to 100m on OM3, and 150m on OM4. There is no support for OM2 or OM1 (these are considered legacy).
  • 40GBASE-LR4 supports up to 10km on SM fiber (same fiber used for 10G single-mode 10GBASE-LR).
  • 40GBASE-CR4 supports up to 7m. The maximum is a limitation of the copper technology, and may not be realistic in all environments.
  • 40GBASE-KR4 specifies up to 1m for backplane technology—this is not applicable to switches and is designed for server blade systems running 40GbE over a backplane.


Q. Can the 40G-LR4 transceiver also be split into 4x10G connections?
A. No, 40G-LR4 cannot be split into 4x10G. The 40GBASE-LR4 uses 4 lambdas (or wavelengths) on a pair of single-mode fibers, and does not lend itself to “splitting” into 4 pairs without substantial complexity to split out the wavelengths. The unique characteristic of 40GBASE-SR4 is that it uses parallel (ribbon) fiber, which allows the creation of 4 fiber pairs. As an alternative single-mode parallel 40G optics are available (40G-PLRL4 and 40G-PLR4) that do allow for splitting into 4x10G. Each of these optics is fully compatible with 10GBASELR and 10G-LRL up to the maximum distance of each optic, and use single mode MTP-12 ribbonfibers.

Q. How does the QSFP+ to SFP+ fiber convertor allow 4x 10G?
A. The IEEE 40G-SR4 standard specified a parallel technology, with 4 lanes in each direction. The purpose of this was to allow for easier development of 40G, re-using 10G components. As a side result the 40G multi-mode transceivers can also support 4x10G modes. (The switch or router also has to support this in both the hardware and software). A fiber that connects from one 40G port to four 10G ports provides a physical path to allow the source “40G” port running in 4x10G mode to be connected to 4 unique 10G destinations. As the fiber is a passive medium it has no concept of the 40G or 10G signals.

Q. What is the 40GbE PLRL4 distance capability?
A. The parallel LR4 Lite (PLRL4) supports distances compatible with 10GBASE-LRL, which is 1km on single-mode fiber. In addition the PLRL4 optic can support 4 individual 10G-LR connections using a 4x10G mode and fiber breakout cables or cassettes for single-mode fiber.

Q. What cable type is needed for the PLRL4 and PLR4 transceivers?
A. The PLR4 and PLRL4 use an MTP-12 connector, and require an APC (Angle polished connector) single-mode MTP-12 cable. The cable is equivalent to the 40G-SR4 MTP to MTP, with the only change being the use of single-mode fiber. UPC (Ultra polished connector) is another type of connector for MTP-12 cables but this does not exist in the market for single-mode fiber. APC is the only available choice for single-mode MTP-12 fiber.

Q. What 40G cables and transceivers are available from Fiberstore?
A.Fiberstore supports a full range of customized 40G transceiver modules to offer versatile 40G & 100G connectivity options in core and distribution layers of data centers, enterprises, and service provider networks etc. For copper, both QSFP+ to QSFP+ (QSFP-H40G-ACU7M) and QSFP+ to SFP+ (QSFP-4X10G-AOC3M) cables enable short reach options. For longer distances, Fiberstore offers a wide range of optical transceivers for various fiber types and reach requirements.

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