2.5GBASE-T and 5GBASE-T

IEEE 802.3bz, NBASE-T and MGBASE-T are standards for Ethernet over twisted pair at speeds of 2.5 Gbit/s and 5 Gbit/s. These use the same cabling as the ubiquitous Gigabit Ethernet, yet offer 2.5x or 5x faster speeds. The resulting standards are named 2.5GBASE-T and 5GBASE-T.[1][2][3] NBASE-T or Multi-Gig also refers to Ethernet equipment that can automatically negotiate to operate at speeds of 100 megabits, 1 gigabit, 2.5 gigabits, 5 gigabits, and/or 10 gigabits, depending on the quality of the cable and the capabilities of the equipment at the other end of the cable.

Technology

These standards are specified in Clauses 125 and 126 of the IEEE 802.3 standard. The physical (PHY) layer transmission technology of IEEE 802.3bz is based on 10GBASE-T, but operates at a lower signaling rate. By reducing the original signal rate to ​1⁄4 or ​1⁄2, the transfer rate drops to 2.5 or 5 Gbit/s, respectively.[4] The spectral bandwidth of the signal is reduced accordingly, lowering the requirements on the cabling, so that 2.5GBASE-T and 5GBASE-T can be deployed at a cable length of up to 100 m on Cat 5e, Cat 6, and Cat 6A cables.[5]

The NBASE-T effort also standardized how its switches can implement Power over Ethernet according to the IEEE 802.3at and successor standards. This allows a single cable to provide both power and data for high-bandwidth wireless access points (802.11ac / 802.11ax).[6]

Comparison of twisted pair based Ethernet technologies
Main article: Ethernet over twisted pair § Variants

Name Speed[upper-alpha 1] (Mbit/s) Lanes per direction Bits per cycle Spectral bandwidth (MHz) Required cable[upper-alpha 2] Cable rating (MHz)
10BASE-T 10 1 1 10 Cat 3 16
100BASE-TX 100 1 3.2 31.25 Cat 5 100
1000BASE‑T 1,000 4 4 62.5 Cat 5 100
2.5GBASE-T 2,500 4 6.25 100 Cat 5e 100
5GBASE-T 5,000 4 6.25 200 Cat 6 250
10GBASE-T 10,000 4 6.25 400 Cat 6A 500
  1. Transfer speed = lanes × bits per hertz × spectral bandwidth
  2. At shorter cable length, it is possible to use cables of a lower grade than what is required for 100 m. For example, it is possible to use 10GBASE-T on a Cat 6 cable of 55 m or less. Likewise, 5GBASE-T is expected to work with Cat 5e in most use cases.

History

These speeds became relevant around 2014 as it became clear that it would not be possible to run 10GBASE-T over already widely deployed Cat5e cable. Also, as faster WiFi protocols such as IEEE 802.11ac were developed, there was significant demand for cheap uplinks faster than 1000BASE-T. IEEE 802.3bz also supports Power over Ethernet, which had previously not been available at 10GBASE-T.

As early as 2013, the Intel Avoton server processors integrated 2.5 Gbit/s Ethernet ports.

Whilst Broadcom had announced a series of 2.5 Gbit/s transceiver ICs,[7] 2.5 Gbit/s switch hardware was not widely commercially available at that point. Many early 10GBASE-T switches, particularly those with SFP+ interfaces, do not support the intermediate speeds.

In October 2014, the NBASE-T Alliance was founded,[8][9] initially comprising Cisco, Aquantia, Freescale, and Xilinx. By December 2015, it contained more than 45 companies, and aimed to have its specification compatible with 802.3bz.[10] The competing MGBASE-T Alliance, stating the same faster Gigabit Ethernet objectives, was founded in December 2014.[11] In contrast to NBASE-T, the MGBASE-T said that their specifications would be open source.[12] IEEE 802.3's "2.5G/5GBASE-T Task Force" started working on the 2.5GBASE-T and 5GBASE-T standards in March 2015.[13] The two NBASE-T and MGBASE-T Alliances ended up collaborating.[14] with the forming of the IEEE 802.3bz Task Force under the patronage of the Ethernet Alliance in June 2015.

On September 23, 2016, the IEEE-SA Standards Board approved IEEE Std 802.3bz-2016.[15]

References
  1. "IEEE P802.3bz 2.5G/5GBASE-T Task Force". IEEE Standards Association.
  2. "New IEEE P802.3bz™ Project Achieves Significant Milestone Towards Enabling Higher Speeds Over Installed Base of Twisted Pair Cabling". IEEE Standards Association.
  3. "IEEE's 802.3BZ Task Force Mediates MGBASE-T and NBASE-T Alliances". Planetech USA. Archived from the original on 2015-11-22. Retrieved 2015-11-22.
  4. "Cisco Live BRKCRS-3900, slide 41, time 57:40". Archived from the original on 2016-03-03. Retrieved 2016-01-15.
  5. Clause 126.7.2 of IEEE 802.3-2018
  6. "Cisco Multigigabit Technology". Retrieved 2020-07-30.
  7. "Broadcom Announces New High-Performance Multi-Rate Gigabit PHYs".
  8. "Industry Leaders Form NBASE-T Alliance to Promote Multi-Gigabit Ethernet Technology for Enterprise Wired and Wireless Access Networks" (Press release). 2014-10-28. Retrieved 2020-07-30.
  9. "The NBASE-T Alliance℠". NBASE-T Alliance, Inc. Retrieved 30 December 2015.
  10. "Oh What a Year!". NBASE-T Alliance, Inc. 2015-12-17. Retrieved 2021-02-04.
  11. "Open Industry Alliance and IEEE to Bring 2.5G and 5G Ethernet Speeds to Enterprise Access Points" (Press release). Retrieved 2020-07-30.
  12. "Want 2.5G/5G BASE-T Connections? They're coming". Retrieved 2020-07-30.
  13. "IEEE 802.3bz Project PAR" (PDF). IEEE 802.3bz Task Force. Retrieved 2015-09-22.
  14. "IEEE's 802.3BZ Task Force Mediates MGBASE-T and NBASE-T Alliances". Archived from the original on 2015-11-22. Retrieved 2015-11-22.
  15. "[802.3_NGBASET] FW: Approval of IEEE Std 802.3bz 2.5GBASE-T and 5GBASE-T". IEEE P802.3bz Task Force. Retrieved 2016-09-24.
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