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 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.
NBASE-T refers to Ethernet equipment that can automatically use training to operate at speeds of 2.5, 5, or 10 Gbit/s, depending on the quality of the cable, in connection with autonegotiation to support additional link speeds (10, 100 or 1000 Mbit/s), depending on the capabilities of the equipment at the other end of the cable.
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 link speed drops to 2.5 or 5 Gbit/s, respectively. 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. The 2.5GBASE-T1 and 5GBASE-T1 variants that can run over a single pair of balanced conductors up to 15 m in length is standardized in 802.3ch-2020; 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.
|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, 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, 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. The competing MGBASE-T Alliance, stating the same faster Gigabit Ethernet objectives, was founded in December 2014. In contrast to NBASE-T, the MGBASE-T said that their specifications would be open source. IEEE 802.3's "2.5G/5GBASE-T Task Force" started working on the 2.5GBASE-T and 5GBASE-T standards in March 2015. The two NBASE-T and MGBASE-T Alliances ended up collaborating. 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.
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- "IEEE's 802.3BZ Task Force Mediates MGBASE-T and NBASE-T Alliances". http://blog.planetechusa.com/2015/06/ieees-802-3bz-task-force-mediates-mgbase-t-and-nbase-t-alliances/.
- "[802.3_NGBASET FW: Approval of IEEE Std 802.3bz 2.5GBASE-T and 5GBASE-T"]. IEEE P802.3bz Task Force. http://www.ieee802.org/3/NGBASET/email/msg00996.html.
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