The Terabit BiDi MSA for Data Centers

Earlier this year, a new Multi-Source Agreement (MSA) comprised of various leading optical companies was announced. This MSA—the Terabit BiDi MSA—will address applications for critical high-volume paths in modern data centers and write specifications for 800G-BiDi over eight multimode fibers and 1.6T-BiDi over sixteen multimode fibers. CommScope is the only fiber cable and connector manufacturer participating in the MSA.

What does BiDi mean?

“BiDi”, short for “bidirectional”, means two optical signals that carry different traffic may counter-propagate on a single fiber without interfering with each other. This is enabled by the optical signals operating at two different wavelengths: typically centered around 850 nm and 910 nm. The two optical signals are multiplexed and demultiplexed using a low-loss, low-cost component known as a diplexer. A diplexer both combines and separates different optical paths that use different wavelengths onto a single fiber. In one lane of a BiDi transceiver, the diplexer will allow an 850 nm signal to pass from the laser (or VCSEL) to the fiber and onto to the far end of the link, while reflecting the incoming 910 nm signal, coming from the far end of the link, into the receiver.  At the other end of the optical link the process is reversed, and the BiDi transceiver there transmits a 910 nm signal into to the fiber and receives an 850 nm signal from the fiber.

A Look at the History of BiDi

The first 40G-BiDi transceivers to be commercially deployed in multimode data center applications were introduced to the market around 2014. These transceivers offered 40G traffic over duplex multimode fibers using two 20G NRZ wavelength channels. This was soon followed by the 100G BiDi transceivers that introduced 50G PAM-4 signals at the same wavelengths and over the same duplex fiber. In 2019, IEEE Ethernet standards included BiDi technology with the 400G-SR4.2 transceiver, which used 50G PAM-4 signals over eight fibers for 400G total transmission.

Since BiDi transceivers use multiple wavelengths, the optimal fiber is one designed for multiwavelength operation. OM5 fiber is designed to provide high bandwidth for a range of wavelengths, including 850 nm and 910 nm. Additionally, OM5 optical fiber has consistently provided longer reaches for BiDi transceivers than was offered by OM4.

The New Multi-Source Agreement (MSA)

The Terabit BiDi MSA aims to build on the success of 40G-BiDi, 100G-BiDi, and 400G-SR4.2. The transceivers specified by the MSA will leverage 100Gb/s VCEL technology and PAM-4 signaling at the same 850 nm and 910 nm wavelengths. 800G-BiDi will use eight-fiber connectivity; 1.6T-BiDi will use sixteen fiber connectivity. The transceiver specifications, including the supported reach, will be determined over the next year.

Why is CommScope participating?

CommScope participates in application standards and MSAs to ensure our products meet the various evolving needs of our customers. Propel™—CommScope’s end-to-end, high-speed fiber platform—is perfectly suited to support BiDi applications, including the new ones from the Terabit BiDi MSA. With OM5 fiber you will have longer reach due to optimized, and additional, multiwavelength support, versus OM4 optical fiber. Propel’s eight-fiber and sixteen-fiber connectivity will interface with the new transceivers for 800G and 1.6T transmission. Once the new transceiver specifications are decided, CommScope’s Fiber Performance Calculator and Application Warranty will be updated to support the Terabit BiDi MSA.

CommScope is focused on providing customers with an advantage—distinguished performance that provides long-term support for evolving network applications. Our customers will benefit from these new BiDi applications that provide for much higher capacity and longer life for their Propel infrastructure investments.