2.5GBASE-T and 5GBASE-T

IEEE 802.3bz, NBASE-T and MGBASE-T refer to efforts to produce a standard for Ethernet over twisted pair copper wire at speeds of 2.5 Gbit/s and 5 Gbit/s. This would create intermediate speeds between existing standards Gigabit Ethernet and 10 Gigabit Ethernet. The resulting standards are expected to be named 2.5GBASE-T and 5GBASE-T.^[1][2]

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.^[3] Adopted IEEE P802.3bz schedule has a planned approval date of September 2016 for the standards.^[4] With pull-in of initial Sponsor Ballot, opportunity exists to complete standards in June 2016.^[5]

The objectives of the task force include:^[6]

• 2.5 Gbit/s up to at least 100m of Cat5e
• 5 Gbit/s up to 100m of Cat5e
• 5 Gbit/s up to at least 100m of Cat6

Technology

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 $\tfrac{1}{4}$ or $\tfrac{1}{2}$, the transfer rate drops to 2.5 or 5 Gbit/s, respectively.^[7] The Nyquist frequency 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 1000BaseT Power over Ethernet connections.^[9]

Comparison of twisted pair based ethernet technologies

Standard	Transfer speed[lower-alpha 1]	Channels per direction[lower-alpha 2]	Bits per Hertz per channel[lower-alpha 3]	Nyquist frequency[lower-alpha 4]	Cable req. 100 m	Cable spec
10BASE-T	10 Mbit/s	1	1	10 MHz	Cat 3	16 MHz
100BASE-TX	100 Mbit/s	1	1.6	62.5 MHz	Cat 5	100 MHz
1000BASE-T	1000 Mbit/s	4	4	62.5 MHz	Cat 5e	100 MHz
2.5GBASE-T	2500 Mbit/s	4	6.25	100 MHz	Cat 5e	100 MHz
5GBASE-T	5000 Mbit/s	4	6.25	200 MHz	Cat 6[lower-alpha 5]	250 MHz
10GBASE-T	10000 Mbit/s	4	6.25	400 MHz	Cat 6A[lower-alpha 5]	500 MHz
40GBASE-T	40000 Mbit/s	4	6.25	1600 MHz	Cat 8 (30 m)	1600/2000 MHz

1. Transfer speed = channels × bits per Hertz × Nyquist frequency
2. On 10BASE-T and 100BASE-TX one twisted pair of the cabling is used for transmission and another for reception, leaving two unused pairs. Highers speeds use all four pairs simultaneously for transmission (TX) and reception (RX).
3. Effective bits per Herz after loss to encoding overhead.
4. The Nyquist frequency is half the symbolrate, except for 10Base-T where it is equal because it uses Manchester code.
5. At cable lengths of 55 m or less, 5GBASE-T and 10GBASE-T is guaranteed to work with CAT 5e and CAT 6, respectively.

History

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]

NBASE-T

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]

References

1. "New IEEE P802.3bz™ Project Achieves Significant Milestone Towards Enabling Higher Speeds Over Installed Base of Twisted Pair Cabling". IEEE Standards Association.
2. "IEEE’s 802.3BZ Task Force Mediates MGBASE-T and NBASE-T Alliances". Planetech USA.
3. "IEEE 802.3bz Project PAR" (PDF). IEEE 802.3bz Task Force. Retrieved 2015-09-22.
4. "IEEE P802.3bz Adopted Schedule" (PDF). IEEE 802.3bz Task Force (Closing Report). p. 5. Retrieved 2015-11-16.
5. "Project Trending Timeline" (PDF). IEEE P802.3bq & P802.3bz Task Force Agenda. p. 14. Retrieved 2016-02-17.
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".
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".
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.

External links

• IEEE P802.3bz 2.5G/5GBASE-T Task Force
• NBASE-T Alliance
• MGBASE-T Alliance