MSA, standards activity paves way for bidirectional 400 Gigabit Ethernet multimode fiber links

This week has seen a pair of advances leveraging bidirectional transmission that promise fewer multimode fibers for 400 Gigabit Ethernet applications than the 32 fibers (16 each for transmit and receive) the original 802.3bs specifications demand. On Monday, the 400G Bidirectional (BiDi) Multi-Source Agreement (MSA) Group announced its intention to specify BiDi optical transceivers for 70- to 150-m multimode fiber applications. Yesterday, the IEEE P802.3cm 400 Gb/s over Multimode Fiber Task Force voted to pursue a similar set of specifications.

This week has seen a pair of advances leveraging bidirectional transmission that promise fewer multimode fibers for 400 Gigabit Ethernet applications than the 32 fibers (16 each for transmit and receive) the original 802.3bs specifications demand. On Monday, the 400G Bidirectional (BiDi) Multi-Source Agreement (MSA) Group announced its intention to specify BiDi optical transceivers for 70- to 150-m multimode fiber applications. Yesterday, the IEEE P802.3cm 400 Gb/s over Multimode Fiber Task Force voted to pursue a similar set of specifications.

The MSA plans to pursue creation of QSFP-DD and OSFP optical transceivers that would have a configuration similar to the 4+4 MPO approach found in 40G and 100G SR4, using two bidirectional wavelengths per fiber at 50 Gbps per transmission. Thus, currently installed infrastructure would have a direct pathway to 400-Gbps support. The specifications would cover up to 70 m on OM3, 100 m on OM4, and 150 m on OM5 fibers. The group expects its specification, which it currently calls 400G-BD4.2, should be ready in the third quarter of this year, at least a year ahead of when the P802.3cm Task Force expects to finish its work.

Founding MSA members include Alibaba, Broadcom, Cisco, Corning Inc., Foxconn Interconnect Technology, InnoLight Technology, Inphi Corp., and Sumitomo Electric. Membership to the MSA is temporarily closed while first draft specifications work progresses; once that work completes, the MSA will accept applications for Contributor Members. Additional info is available on the MSA’s website.

The site FAQ says the group plans to style its efforts on an IEEE model, in hopes that the IEEE will be able to leverage its work. The success of that approach was demonstrated yesterday, when the P802.3cm Task Force adopted a motion to pursue development of a similar set of specifications, which they dubbed 400GBASE-SR4.2. SR4.2 will address the same reach/multimode fiber type combinations as the MSA, using bi-directional optical multiplexing of 50-Gbps transmissions at ~850 nm and ~910 nm.

“In my discussions and travels, I personally find strong interest in 400G-SR4.2 in the big cloud in China and North America,” commented Robert Lingle, chair of the Task Force. “It will be a popular transceiver in large enterprise data centers as well, supporting the large installed base of MPO-12 terminated cabling installed for 40 and 100GBASE-SR4.”

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