100G Gearbox with RS-FEC Solution for QSFP28-Based Optics with the MoSys LineSpeed™ Flex PHY IC

By Scott Irwin
Vice President, LineSpeed Products
MoSys, Inc.

Worldwide shipments and revenue for 100Gb Ethernet switches have been growing rapidly, reaching 3.8M ports and $1.1B revenue for Q4 of 2018, according to IDC.  This has been driven by accelerating adoption in cloud datacenter and large enterprise markets.  This can also be seen echoed in the growth of 100G optical transceiver modules used to interconnect switching, routing, computing, and other equipment. A range of 100G optical module types have been created through standards development organizations (SDOs) and Multi-Source Agreement (MSAs) to meet various reach, cost, and other market requirements.

The latest of these optical module standards now require Reed Solomon – Forward Error Correction (RS-FEC) encoding to extend the reach and/or reliability of these 100G optical links.  This RS-FEC encoding, as defined by the IEEE in 802.3bj, is applied to the 4x25G interfaces commonly used to connect these 100GE optical modules, such as QSFP28 pluggable modules. Unfortunately, this RS-FEC encoding cannot be applied at the original 10x10G signaling interfaces used in earlier 100GE standards and is incompatible with the 10x10G-to-4x25G “Gearbox” function as defined in IEEE 802.3ba. This makes it difficult to utilize FPGAs and ASICs with lower-speed SerDes (10-11G) to implement the latest 100GE interfaces.

The MoSys MSH320SF Gearbox device with optional RS-FEC encode/decode allows:

  • A lower-cost FPGA with 10-11G SerDes to interface to all QSFP28-based optics
  • Can support 100G optical modules with either
    • Non-FEC (e.g. LR4)
    • Or FEC-based (e.g. SR4, CWDM4, PSM4, etc.) standards
  • Its 10G Retimer capability can also support backward compatibility to 40G (4x10G) pluggable modules in the same port
  • The MSH320SF is production ready and priced at $50 in volume.

Features and benefits of the MSH320SF Gearbox device include:

The MSH320SF, coupled with a low-cost FPGA, is the perfect solution for your QSFP28-based interface.  A single footprint can support both FEC and non-FEC 100G modules, along with backward-compatible support to 40G modules.

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