IEEE 802.3bz, NBASE-T and MGBASE-T are standards for Ethernet over twisted pair at speeds of 2.5 and 5 Gbit/s. These use the same cabling as the ubiquitous Gigabit Ethernet, yet offer higher speeds. The resulting standards are named 2.5GBASE-T and 5GBASE-T.[1][2][3]

NBASE-T refers to Ethernet equipment that can automatically negotiate to operate at speeds of 100 Mbit/s, 1, 2.5, 5, or 10 Gbit/s, depending on the quality of the cable and the capabilities of the equipment at the other end of the cable.[citation needed]


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 14 or 12, the link speed 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 or better cables.[5][6] The 2.5GBASE-T1 and 5GBASE-T1 variants that can run over a single pair of balance conductors up to 15 m in length is standardized in 802.3ch-2020;[7] their primary use case field is in embedded automotive applications.

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 such as those that implement the 802.11ac and 802.11ax standards.[8]

Comparison of twisted-pair-based Ethernet physical transport layers (TP-PHYs)[9]
Name Standard Status Speed (Mbit/s) Pairs required Lanes per direction Bits per hertz Line code Symbol rate per lane (MBd) Bandwidth Max distance (m) Cable Cable rating (MHz) Usage
2.5GBASE-T 802.3bz-2016 current 2500 4 4 6.25 64B65B PAM-16 128-DSQ 200 100 100 Cat 5e 100 LAN
5GBASE-T 802.3bz-2016 current 5000 4 4 6.25 64B65B PAM-16 128-DSQ 400 200 100 Cat 6 250 LAN


As faster Wi-Fi protocols such as IEEE 802.11ac were developed, there was significant demand for cheap uplinks faster than 1000BASE-T. 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. 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,[10] 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,[11][12] 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.[13] The competing MGBASE-T Alliance, stating the same faster Gigabit Ethernet objectives, was founded in December 2014.[14] In contrast to NBASE-T, the MGBASE-T said that their specifications would be open source.[15] IEEE 802.3's "2.5G/5GBASE-T Task Force" started working on the 2.5GBASE-T and 5GBASE-T standards in March 2015.[16] The two NBASE-T and MGBASE-T Alliances ended up collaborating.[17] 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.[18]


  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. ^ Next Generation Enterprise Access BASE-T PHY Objectives
  7. ^ Maguire, Valerie (2020-06-04). "IEEE Std 802.3ch-2020: Multi-Gig Automotive Ethernet PHY".
  8. ^ "Cisco Multigigabit Technology". Retrieved 2020-07-30.
  9. ^ Charles E. Spurgeon (2014). Ethernet: The Definitive Guide (2nd ed.). O'Reilly Media. ISBN 978-1-4493-6184-6.
  10. ^ "Broadcom Announces New High-Performance Multi-Rate Gigabit PHYs". Archived from the original on 2015-05-29. Retrieved 2015-05-28.
  11. ^ "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.
  12. ^ "The NBASE-T Alliance℠". NBASE-T Alliance, Inc. Retrieved 30 December 2015.
  13. ^ "Oh What a Year!". NBASE-T Alliance, Inc. 2015-12-17. Retrieved 2021-02-04.
  14. ^ "Open Industry Alliance and IEEE to Bring 2.5G and 5G Ethernet Speeds to Enterprise Access Points" (Press release). Retrieved 2020-07-30.
  15. ^ "Want 2.5G/5G BASE-T Connections? They're coming". Retrieved 2020-07-30.
  16. ^ "IEEE 802.3bz Project PAR" (PDF). IEEE 802.3bz Task Force. Retrieved 2015-09-22.
  17. ^ "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.
  18. ^ "[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.

External links

  • IEEE P802.3bz 2.5G/5GBASE-T Task Force
  • NBASE-T Alliance
  • MGBASE-T Alliance at the Wayback Machine (archived 2017-11-05)