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 802.3by[1] and 802.3cd[2] and are available from multiple vendors.

History

An industry consortium, 25G Ethernet Consortium,[3] 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,[4][5] and in November 2015, a study group was formed to explore the development of a single-lane 50-Gbit/s standard.[6]

In May 2016, an IEEE 802.3 task force was formed to develop a single-lane 50 Gigabit Ethernet standard.[2]

On June 30, 2016, the IEEE 802.3by standard was approved by The IEEE-SA Standards Board.[7]

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.[8]

The IEEE 802.3cd standard was approved on December 5, 2018.

On December 20, 2019, the IEEE 802.3cn standard was published. [9]

On April 6, 2020, 25 Gigabit Ethernet Consortium has rebranded to Ethernet Technology Consortium, and it announces 800 Gigabit Ethernet (GbE) specification.[10]

25 Gigabit Ethernet

The IEEE 802.3by standard uses technology defined for 100 Gigabit Ethernet implemented as four 25-Gbit/s lanes (IEEE 802.3bj).[11][12] The IEEE 802.3by standard several single-lane variations.[13]

25GBASE-T, a 25-Gbit/s standard over twisted pair, was approved alongside 40GBASE-T within IEEE 802.3bq.[14][15]

Legend for fibre-based TP-PHYs[16]
MMF
FDDI
62,5/125 µm
(1987)		 MMF
OM1
62,5/125 µm
(1989)		 MMF
OM2
50/125 µm
(1998)		 MMF
OM3
50/125 µm
(2003)		 MMF
OM4
50/125 µm
(2008)		 MMF
OM5
50/125 µm
(2016)		 SMF
OS1
9/125 µm
(1998)		 SMF
OS2
9/125 µm
(2000)
160 MHz·km
@850 nm		 200 MHz·km
@850 nm		 500 MHz·km
@850 nm		 1500 MHz·km
@850 nm		 3500 MHz·km
@850 nm		 3500 MHz·km
@850 nm &
1850 MHz·km
@950 nm		 1 dB/km
@1300/
1550 nm		 0.4 dB/km
@1300/
1550 nm
Name Standard Status Media OFC or RFC Transceiver
Module		 Reach
(meters)		 #
Media		 Lanes
(⇅)		 Notes
25 Gigabit Ethernet (25 GbE) - (Data rate: 25 Gbit/s - Line code: 64b/66b with RS-FEC × NRZ - Line rate: 25.7813 GBd - Full-Duplex) [17]
25GBASE
-CR
Direct Attach		 802.3by-2016
(CL110)		 current twinaxial
balanced		 SFP28
(SFF-8402)		 SFP28 5 2 1 Data centres (inter-rack)
25GBASE
-CR-S
Direct Attach		 802.3by-2016
(CL110)		 current twinaxial
balanced		 SFP28
(SFF-8402)		 SFP28 3 1 1 Data centres (in-rack);
without RS-FEC (802.3by CL108)
25GBASE
-KR		 802.3by-2016
(CL111)		 current Cu-Backplane N/A N/A 1 1 2 PCBs
25GBASE
-KR-S		 802.3by-2016
(CL111)		 current Cu-Backplane N/A N/A 1 1 1 PCBs;
without RS-FEC (802.3by CL108)
25GAUI 802.3by-2016
(CL109A/B)		 current Cu-Backplane N/A N/A 0.25 2 1 PCBs: Chip-to-chip / chip-to-module interface
25GBASE
-SR		 802.3by-2016
(CL112)		 current Fibre
850 nm		 LC SFP28 70 OM3 2 1
100 OM4
25GBASE
-LR		 802.3cc-2017
(CL114)		 current Fibre
1295 – 1325 nm		 LC SFP28 10000 OS2 2 1
25GBASE
-ER		 802.3cc-2017
(CL114)		 current Fibre
1550 nm		 LC SFP28 40000 OS2 2 1
Name Clause (standard) Medium Media Count Gigabaud per lane Reach RS-FEC (802.3by clause 108)
25GBASE-T 113 (802.3bq) Cat 8 balanced twisted-pair structured cabling 4 pairs 2.000 30 m No

50 Gigabit Ethernet

The IEEE P802.3cd [2] standard defines a Physical Coding Sublayer (PCS) in Clause 133 which after encoding gives a data rate of 51.5625 Gbit/s. 802.3cd also defines an RS-FEC for forward error correction in Clause 134 which after FEC encoding gives a data rate of 53.125 Gbit/s. It is not possible to transmit 53.125 Gbit/s over an electrical interface while maintaining suitable signal integrity so four-level pulse amplitude modulation (PAM4) is used to map pairs of bits into a single symbol. This leads to an overall baud rate of 26.5625 GBd for 50 Gbit/s per lane Ethernet. PAM4 encoding for 50G Ethernet is defined in Clause 135 of the 802.3 standard.

Legend for fibre-based TP-PHYs[16]
MMF
FDDI
62,5/125 µm
(1987)		 MMF
OM1
62,5/125 µm
(1989)		 MMF
OM2
50/125 µm
(1998)		 MMF
OM3
50/125 µm
(2003)		 MMF
OM4
50/125 µm
(2008)		 MMF
OM5
50/125 µm
(2016)		 SMF
OS1
9/125 µm
(1998)		 SMF
OS2
9/125 µm
(2000)
160 MHz·km
@850 nm		 200 MHz·km
@850 nm		 500 MHz·km
@850 nm		 1500 MHz·km
@850 nm		 3500 MHz·km
@850 nm		 3500 MHz·km
@850 nm &
1850 MHz·km
@950 nm		 1 dB/km
@1300/
1550 nm		 0.4 dB/km
@1300/
1550 nm
Name Standard Status Media OFC or RFC Transceiver
Module		 Reach
(meters)		 #
Media		 Lanes
(⇅)		 Notes
50 Gigabit Ethernet (50 GbE) - (Data rate: 50 Gbit/s - Line code: 256b/257b × RS-FEC(544,514) × PAM4 - Line rate: 26.5625 GBd - Full-Duplex) - Full-Duplex) [18][19]
50GBASE
-CR		 802.3cd-2018
(CL133/136)		 current twinaxial
balanced		 SFP56
(SFF-8402)		 SFP56 3 1 1 Data centres (in-rack)
50GBASE
-KR		 802.3cd-2018
(CL133/137)		 current Cu-Backplane N/A N/A 1 1 1 PCBs;
total channel insertion loss ≤ 30 dB at half sampling rate = 13.28125 GHz (Nyquist).
50GBASE
-SR		 802.3cd-2018
(CL133/138)		 current Fibre
850 nm		 LC SFP56 70 OM3 2 1
100 OM4
50GBASE
-LR		 802.3cd-2018
(CL133/139)		 current Fibre
1304.5 – 1317.5 nm		 LC SFP56 10000 OS2 2 1
50GBASE
-FR		 802.3cd-2018
(CL133/139)		 current Fibre
1304.5 – 1317.5 nm		 LC SFP56 2000 OS2 2 1
50GBASE
-ER		 802.3cn-2019
(CL133/139)[8]		 current Fibre
1304.5 – 1317.5 nm		 LC SFP56 40000 OS2 2 1
LAUI-2 802.3cd-2018
(CL135B/C)		 current Cu-Backplane N/A N/A 0.25 2 2 PCBs: Chip-to-chip/chip-to-module interface;
Line code: NRZ (no FEC)
Line rate: 2x 25.78125 GBd = 51.5625 GBd
50GAUI-2 802.3cd-2018
(CL135D/E)		 current Cu-Backplane N/A N/A 0.25 2 2 PCBs: Chip-to-chip/chip-to-module interface;
Line code: NRZ (FEC encoded)
Line rate: 2x 26.5625 GBd = 53.125 GBd
50GAUI-1 802.3cd-2018
(CL135F/G)		 current Cu-Backplane N/A N/A 0.25 1 1 PCBs: Chip-to-chip/chip-to-module interface

Availability

As of June 2016, 25 Gigabit Ethernet equipment is available on the market using the SFP28 and QSFP28 transceiver form factors. Direct attach SFP28-to-SFP28 copper cables in 1-, 2-, 3- and 5-meter lengths are available from several manufacturers, and optical transceiver manufacturers have announced 1310 nm "LR" optics intended for reach distances of 2 to 10 km over two strands of standard singlemode fiber, similar to existing 10GBASE-LR optics, as well as 850 nm "SR" optics intended for short reach distances of 100 m over two strands of OM4 multimode fiber, similar to existing 10GBASE-SR optics.

See also

References
  1. IEEE 802.3by 25 Gb/s Ethernet Task Force
  2. IEEE 802.3cd 50 Gb/s, 100 Gb/s, and 200 Gb/s Ethernet Task Force
  3. "25G Ethernet Consortium". Retrieved 2017-09-17.
  4. Rick Merritt (2014-07-21). "25G Ethernet on Tap at IEEE". Retrieved 2014-09-29.
  5. "IEEE 802.3 25 Gb/s Ethernet Study Group Public Area". IEEE 802.3. 2014-10-29. Retrieved 2014-12-31.
  6. "Joint Webpage for IEEE 802.3 50 Gb/s Ethernet Over a Single Lane and Next Generation 100 Gb/s and 200 Gb/s Ethernet Study Group IEEE 802.3 200 Gb/s Ethernet Single-mode Fiber Study Group". Retrieved 2017-09-17.
  7. "[STDS-802-3-25G] IEEE Std 802.3by-2016 Standard Approved!". 2016-06-30.
  8. http://www.ieee802.org/3/cn/proj_doc/3cn_Objectives_181113.pdf
  9. http://www.ieee802.org/3/email_dialog/msg01004.html
  10. "25 Gigabit Ethernet Consortium Rebrands to Ethernet Technology Consortium; Announces 800 Gigabit Ethernet (GbE) Specification". 2020-04-06.
  11. "Overview 25G & 50G Ethernet Specification, Draft 1.4" (PDF). 25G Ethernet Consortium. 2014-09-11. Retrieved 2014-12-31.
  12. Stephen Hardy (July 23, 2014). "IEEE launches 25 Gigabit Ethernet Study Group". LightWave. Retrieved 2014-09-29.
  13. "Adopted & Approved Objectives: 25 Gb/s Ethernet over a single lane for server interconnect" (PDF). Retrieved 2017-09-17.
  14. "IEEE P802.3bq 25G/40GBASE-T Task Force". Retrieved 2016-02-08.
  15. "Approval of IEEE Std 802.3by-2016, IEEE Std 802.3bq-2016, IEEE Std 802.3bp-2016 and IEEE Std 802.3br-2016". IEEE. 2016-06-30.
  16. Charles E. Spurgeon (2014). Ethernet: The Definitive Guide (2nd ed.). O'Reilly Media. ISBN 978-1-4493-6184-6.
  17. "Evolution of Ethernet Speeds: What's New and What's Next" (PDF). Alcatel-Lucent. 2015-06-03. Retrieved 2018-08-28.
  18. "Exploring The IEEE 802 Ethernet Ecosystem" (PDF). IEEE. 2017-06-04. Retrieved 2018-08-29.
  19. "Multi-Port Implementations of 50/100/200GbE" (PDF). Brocade. 2016-05-22. Retrieved 2018-08-29.
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