25 Gigabit Ethernet
25 Gigabit Ethernet and 50 Gigabit Ethernet are standards for Ethernet connectivity in a datacenter environment, developed by IEEE 802.3 task forces and and are available from multiple vendors.
History
An industry consortium, 25G Ethernet Consortium, was formed by Arista, Broadcom, Google, Mellanox Technologies and Microsoft in July 2014 to support the specification of single-lane 25-Gbit/s Ethernet and dual-lane 50-Gbit/s Ethernet technology. The 25G Ethernet Consortium specification draft was completed in September 2015 and uses technology from IEEE Std. 802.3ba and IEEE Std. 802.3bj.In November 2014, an IEEE 802.3 task force was formed to develop a single-lane 25-Gbit/s standard, and in November 2015, a study group was formed to explore the development of a single-lane 50-Gbit/s standard.
In May 2016, an IEEE 802.3 task force was formed to develop a single-lane 50 Gigabit Ethernet standard.
On June 30, 2016, the IEEE 802.3by standard was approved by The IEEE-SA Standards Board.
On November 12, 2018, the IEEE P802.3cn Task Force started working to define PHY supporting 50-Gbit/s operation over at least 40 km of SMF.
The IEEE 802.3cd standard was approved on December 5, 2018.
On December 20, 2019, the IEEE 802.3cn standard was published.
On April 6, 2020, 25 Gigabit Ethernet Consortium rebranded to Ethernet Technology Consortium, and announced an 800 Gigabit Ethernet specification.
On June 4, 2020, the IEEE approved IEEE 802.3ca, which allows for symmetric or asymmetric operation with downstream speeds of 25 or, and upstream speeds of 10, 25, or over passive optical networks.
25 Gigabit Ethernet
The IEEE 802.3by standard uses technology defined for 100 Gigabit Ethernet implemented as four 25-Gbit/s lanes. The IEEE 802.3by standard defines several single-lane variations.;
| Name | Standard | Status | Speed | Pairs | Lanes per | Bits per hertz | Line code | Symbol rate per lane | Max | Cable | Cable rating | Usage | |
| 25000 | 4 | 4 | 6.25 | PAM-16 RS-FEC LDPC | 2000 | 1000 | 30 | Cat 8 | 2000 | LAN, Data centres |
Forward Error Correction
All fibre and twisted pair versions of 25 Gigabit Ethernet are required to support Reed-Solomon Forward Error Correction, often abbreviated RS-FEC, defined in clause 108 of the IEEE 802.3 standard. This also applies to 25GBASE-CR but not to 25GBASE-CR-S, both of which are variants used in DAC cables. 25GBASE-CR as well as 25GBASE-CR-S are required to support Fire-Code FEC. While RS-FEC has to be supported for the mentioned 25 G versions, clause 108 also mandates that it has to be possible to turn FEC off, which makes it possible to not use FEC if desired.For an Ethernet link to form, the interfaces involved must use the same type of FEC or no FEC.