IEEE 802.3bz, NBASE-T and MGBASE-T refer to standards for Ethernet over twisted pair at speeds of 2.5 Gbit/s and 5 Gbit/s. This represents intermediate speeds between Gigabit Ethernet and 10 Gigabit Ethernet. The resulting standards are named 2.5GBASE-T and 5GBASE-T.[1][2][3]

IEEE 802.3bz

IEEE 802.3's "2.5G/5GBASE-T Task Force" started working on the 2.5GBASE-T and 5GBASE-T standards in March 2015.[4]

On September 23, 2016, The IEEE-SA Standards Board approved IEEE Std 802.3bz-2016.[5]

The IEEE Standard 802.3bz defines:[6]

  • 2.5 Gbit/s up to at least 100 m of Cat 5e
  • 5 Gbit/s up to at least 100 m of Cat 6
  • 5 Gbit/s up to 100 m of Cat 5e "on defined use cases and deployment configurations"


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 transfer rate drops to 2.5 or 5 Gbit/s, respectively.[7] 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 100 m on unshielded Cat 5e and Cat 6 twisted-pair cables, respectively.[8]

Power over Ethernet

Unlike the preceding 10GBASE-T standard, equipment manufacturers have indicated their intention to implement 802.3at type Power over Ethernet on certain types of NBASE-T switches. This implementation is intended to support high-bandwidth wireless access points (802.11ac / 802.11ax) which exceed the speed capabilities of existing 1000BASE-T Power over Ethernet connections.[9]

Comparison of twisted pair based Ethernet technologies

Name Speed[upper-alpha 1]
req. [upper-alpha 2]
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 5e 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.


The intermediate speeds became relevant around 2014 as it became clear that it would not be possible to run 10GBASE-T over the Cat5e cable that had been used for the wiring in many buildings but that, with the development of fast WiFi protocols such as IEEE 802.11ac, there was a significant demand for cheap uplink faster than 1000BASE-T offered. IEEE 802.3bz will also support Power over Ethernet, which has generally 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; 10GBASE-T switches do not generally support the intermediate speeds.

In October 2014 the NBASE-T Alliance was founded,[11] initially comprising Cisco, Aquantia, Freescale and Xilinx. By May 2015 [12] it had expanded to 34 members covering most producers of networking hardware.

The competing MGBASE-T Alliance, stating the same faster Gigabit Ethernet objectives, was founded in December 2014.[13] In contrast to NBASE-T, the MGBASE-T says that their specifications will be open source.[14]

With the forming of the IEEE 802.3bz draft standard under the patronage of the Ethernet Alliance in June 2015, the two NBASE-T and MGBASE-T Alliances are forced to collaborate.[15]


The NBASE-T Alliance was founded in 2014 by Aquantia Corporation, Cisco Systems, Freescale Semiconductor and Xilinx.[16] It now consists of more than 45 companies, and aims to have their specification compatible with 802.3bz.[17]


  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. "IEEE 802.3bz Project PAR" (PDF). IEEE 802.3bz Task Force. Retrieved 2015-09-22.
  5. "[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.
  6. "Next Generation Enterprise Access BASE-T PHY Objectives" (PDF). IEEE P802.3bz 2.5G/5GBASE-T Task Force.
  7. "Cisco Live BRKCRS-3900, slide 41, time 57:40". Archived from the original on 2016-03-03. Retrieved 2016-01-15.
  8. "Technology". NBASE-T. NBASE-T Alliance. 2015. Retrieved 2015-10-18.
  9. "Cisco NBaseT switches".
  10. "Broadcom Announces New High-Performance Multi-Rate Gigabit PHYs".
  11. "Industry Leaders Form NBASE-T Alliance to Promote Multi-Gigabit Ethernet Technology for Enterprise Wired and Wireless Access Networks".
  12. "NBASE-T Alliance Jumps to 34 Members".
  13. "Open Industry Alliance and IEEE to Bring 2.5G and 5G Ethernet Speeds to Enterprise Access Points".
  14. "Want 2.5G/5G BASE-T Connections? They're coming".
  15. "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.
  16. "The NBASE-T Alliance℠". NBASE-T Alliance, Inc. Retrieved 30 December 2015.
  17. "Oh What a Year!". NBASE-T Alliance, Inc. Retrieved 30 December 2015.
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