While the clock rate of a 40G MAC can be reduced to build a 25G Ethernet MAC, users of 25G Ethernet who are replacing 10G will still want many of the features existing in 10G Ethernet today. Some examples include the need for real-time networking as supported by IEEE 1588-2008 and AVB standards and is being expanded on by the Time Sensitive Networking (TSM) Task Group in the IEEE. Networking features such as VxLAN, NVGRE. EEE and SDN are also requirements in today’s systems.
In best practices, a 25G MAC is designed to run at higher Enterprise networking speeds such as 50G without timing violations to ease future migrations.
The SerDes technology for 25G Ethernet is defined in IEEE P802.3bj as a 25GB 4 lane electrical interface and is available today. The PCS associated with the SerDes can be based on an existing IEEE standard, or may require some updates depending on updates and/or adoption of the existing FEC clauses in the IEEE specifications.
The 100G Ethernet standards exist now and can be used for 25G Ethernet: 100GBASE-LR4, 100GBASE-ER4 for single mode fiber, 100GBASE-SR4 for multimode fiber, 100GBASE-CR4 and 10GBASE-KR4 for 4x25G over twinax and backplane.