2.5GBASE-T and 5GBASE-T
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. These represent intermediate speeds between Gigabit Ethernet and 10 Gigabit Ethernet, potentially allowing for faster speeds over existing cabling. The resulting standards are named 2.5GBASE-T and 5GBASE-T. They are both specified in Clauses 125 and 126 of the current 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. 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.
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 1000BASE-T.
Comparison of twisted pair based Ethernet technologies
|Name||Speed[A] (Mbit/s)||Lanes per direction||Bits per cycle||Spectral bandwidth (MHz)||Required cable[B]||Cable rating (MHz)|
- Transfer speed = lanes × bits per hertz × spectral bandwidth
- 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, 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, initially comprising Cisco, Aquantia, Freescale, and Xilinx. By May 2015, 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. In contrast to NBASE-T, the MGBASE-T says that their specifications will be open source.
On September 23, 2016, the IEEE-SA Standards Board approved IEEE Std 802.3bz-2016.
The NBASE-T Alliance was founded in 2014 by Aquantia Corporation, Cisco Systems, Freescale Semiconductor, and Xilinx. It now consists of more than 45 companies, and it aims to have its specification compatible with 802.3bz.
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