Drives Development of Low Cost 400 Gbits/s Multimode Datacentre Links
The 400G Bidirectional (BiDi) Multi-Source Agreement (MSA) Group has announced its formation as an industry consortium. Its aim is to promote adoption of interoperable 400 Gbits/s optical transceivers for 100 metre multimode fibre (MMF) link distances. The MSA is dedicated to defining optical data link specifications based on a dual wavelength bidirectional transmission technology which enables a reduction in the fibre count relative to other solutions. The target solution leverages both the widely adopted 40 Gbits/s and 100 Gbits/s BiDi Ethernet solutions, and is compatible with the widely available and deployed parallel MMF cabling infrastructure.
Founding members of the 400G BiDi MSA include Alibaba, Broadcom, Cisco, Corning Incorporated, Foxconn Interconnect Technology, InnoLight Technology, Inphi Corporation and Sumitomo Electric.
The 400G BiDi MSA specification addresses short reach applications, including the critical high-volume reaches in modern datacentres between switches. The 400G BiDi MSA participants say they are responding to an industry need for lower cost and lower power consumption solutions in 400 Gbits/s form factors that bidirectional multimode technology can provide.
The key features of 400G BiDi solutions are as follows.
Optical bidirectional technology allows each single fibre to carry signals in both directions, thereby improving fibre utilisation relative to existing 400G MMF standards. For a 100G BiDi link, one fibre pair is required (consistent with commonly installed infrastructure such as a duplex LC) running 53.125 Gbits/s on each fibre in both directions for an aggregate of 106.25 Gbits/s. The 400G BiDi specification is a quad version of the 100G BiDi approach, utilising four fibre pairs (consistent with commonly installed infrastructure such as a 4+4 fibre MPO). For all BiDi implementations, only one laser is launched into each fibre end, simplifying optical design and keeping costs low.
The 400G BiDi specification defines the 50 Gbits/s per lane PAM-4 optical signalling, modulation encoding, lane assignments and link characteristics for 400 Gbits/s MMF Ethernet applications. It does not define a physical form factor, FEC or electrical interface.
The specification will be named 400G-BD4.2, to identify the bidirectional use of four lasers, each of two colours. Using the 400G-BD4.2 specification, two transceivers communicate over lengths up to 70 metres (OM3), 100 metres (OM4) and 150 metres (OM5).
The MSA anticipates that the first specification will be publicly released in Q3 calendar 2018.