IEEE 802.3by™ ”IEEE Standard for Ethernet Amendment: Media Access Control Parameters, Physical Layers and Management Parameters for 25 Gb/s Operation” is currently under development by the IEEE P802.3by 25 Gb/s Ethernet Task Force and anticipated to publish in September, 2016. 25 Gb/s has been identified as a cost-optimized step on the migration path to 400 Gb/s speeds and will maximize the efficiency of server to first-level equipment (i.e. Top-of-Rack, access layer, and leaf) connections. This project will define 25 Gb/s Physical Layer (PHY) specifications for operation over up to 100 m of multimode optical fiber cabling and up to 5 m of a single lane (two pairs) of twinaxial cable and attachment interfaces supporting 25 Gb/s transmission in electrical backplanes. The recognized direct attach twinaxial cable assembly form factors are SFP28 to SFP28, QSFP28 to QSFP28, and QSFP28 to 4 x SFP28.
The five new PHY specifications are as follows:
25GBASE-CR: 25 Gb/s using 25GBASE-R encoding over one lane of twinaxial copper cable
25GBASE-CR-S: Equivalent to 25GBASE-CR without support for the RS-FEC sublayer
25GBASE-KR: 25 Gb/s using 25GBASE-R encoding over one lane of an electrical backplane
25GBASE-KR-S: Equivalent to 25GBASE-KR without support for the RS-FEC sublayer
25GBASE-SR: 25 Gb/s using 25GBASE-R encoding over multimode fiber
The IEEE 802.3 25 Gb/s Ethernet Call-For-Interest Consensus Presentation can be found here: http://www.ieee802.org/3/cfi/0714_1/CFI_01_0714.pdf
The current focus of the IEEE P802.3by 25 Gb/s Ethernet Task Force is circulating their draft document for Sponsor ballot review and resolving comments.
The Project Authorization Request (PAR), approved on December 10, 2014, can be found here: http://www.ieee802.org/3/by/P802_3by_PAR_approved_121214.pdf
The project objectives, adopted on November 6, 2014, (refer to: http://www.ieee802.org/3/by/P802_3by_Objectives.pdf) are as follows.
- Support a MAC data rate of 25 Gb/s
- Support full-duplex operation only
- Preserve the Ethernet frame format utilizing the Ethernet MAC
- Preserve minimum and maximum FrameSize of current IEEE 802.3 Standard
- Support a BER of better than or equal to 10-12 at the MAC/PLS service interface (or the frame loss ratio equivalent)
- Support optional Energy-Efficient Ethernet operation
- Define a single-lane 25 Gb/s PHY for operation over a printed circuit board backplane consistent with channels specified in IEEE Std 802.3bj-2014 Clause 93
- Define a single-lane PHY for operation over links consistent with copper twin axial cables, with lengths up to at least 3m
- Define a single-lane PHY for operation over links consistent with copper twin axial cables, with lengths up to at least 5m
- Define a single-lane PHY for operation over MMF consistent with IEEE P802.3bm Clause 95
- Provide appropriate support for OTN