Data Center

FAQ about 40G Optical Network


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 9um 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 the switches and is designed for server blade systems running 40GbE over a backplane

Q. What is the 40GbE XSR4 max supported distances?
A. The SR4 (XSR4) supports distances compatible with 10GBASE-SR, up to 300m on OM3 and 400m on OM4. The 40G XSR4 is also capable of running as 4x10G, with full compatibility with 10G-SR and 10G-SRL transceivers. Operation in 4x10G mode will require either a fiber breakout cable, or a QSFP-LC cassette. See below for details.

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.