Standards for Ethernet over twisted-pair cables at multi-gigabit speeds
IEEE 802.3bz
,
NBASE-T
and
MGBASE-T
are standards released in 2016 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 supports speeds of at least 2.5 Gbit/s and sometimes 5 or 10 Gbit/s, and that can automatically use training to operate at the best speed supported by the cable quality.
[4]
Usually it also supports additional link speeds (10, 100 or 1000 Mbit/s) in connection with
autonegotiation
, depending on the capabilities of the equipment at the other end of the cable.
[
citation needed
]
Technology
[
edit
]
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.
[5]
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.
[6]
[7]
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]
Prior to the release of 2.5GBASE-T and 5GBASE-T, manufacturers of wireless access points that wanted to support multi-gigabit uplink speed using standard gigabit Ethernet ports had to include multiple Ethernet ports on their access points. By bonding the connections from multiple Ethernet ports via IEEE 802.3ad link aggregation or similar, manufacturers were able to achieve speeds close to
2 Gbit/s
with 2 gigabit ports. This would require the wireless access point to be connected to the rest of the network with 2 Ethernet cables and require both the wireless access point and network hardware to support and be configured for link aggregation. Wireless access points that support 2.5GBASE-T or 5GBASE-T eliminate this complexity.
Comparison of
twisted-pair-based Ethernet
physical transport layers (TP-PHYs)
[9]
Name
|
Standard
|
Status
|
Speed (Mbit/s)
|
Pairs required
|
Lanes per direction
|
Spectral Efficiency (Bits per hertz)
|
Line code
|
Symbol rate
per lane (MBd)
|
Bandwidth (MHz)
|
Max distance (m)
|
Cable
|
Cable rating (MHz)
|
Usage
|
2.5GBASE-T
|
802.3bz-2016
|
current
|
2500
|
4
|
4
|
6.25
|
64b66b
PAM-16
128-DSQ
|
200
|
100
|
100
|
Cat 5e
or
Cat 6
[6]
|
100
|
LAN
|
5GBASE-T
|
802.3bz-2016
|
current
|
5000
|
4
|
4
|
6.25
|
64b66b PAM-16 128-DSQ
|
400
|
200
|
100
|
Cat 5e
or
Cat 6
[6]
|
250
|
LAN
|
10GBASE-T
|
802.3an-2006
|
current
|
10000
|
4
|
4
|
6.25
|
64b66b PAM-16 128-DSQ
|
800
|
400
|
100
|
Cat 6A
|
500
|
LAN
|
History
[
edit
]
In 2013 with the release of
IEEE 802.11ac
(WiFi 5), wireless access points for the first time could reach speeds of
2 Gbit/s
or
4 Gbit/s
, exceeding the
1 Gbit/s
IEEE 802.3ab
1000BASE-T
wired Ethernet uplink. While 10GBASE-T had already been standardized since 2006, this standard used a higher signaling frequency that would have substantially limited the maximum distance of
Cat5e cable
runs. Therefore, there was demand for an intermediate standard that could uplink the
2 Gbit/s
and
4 Gbit/s
speeds from wireless access points over existing
Cat5e cable
. The development of the 2.5GBASE-T and 5GBASE-T standards enabled wireless access points to reach their maximum speeds without being limited by the Ethernet uplink speeds over a single existing Cat5e cable, while also being compatible with newer Cat6 and Cat6a cabling.
[10]
The 2.5GBASE-T and 5GBASE-T standards also serve as an interim solution for achieving lower-cost and lower power consumption multi-gigabit network speeds. As of Dec 2022, 10GBASE-T network equipment is still substantially more expensive than 1GBASE-T, 2.5GBASE-T, and 5GBASE-T network equipment.
IEEE 802.3bz also supports
power over Ethernet
, which had previously not been available with IEEE 802.3an 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,
[11]
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,
[12]
[13]
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.
[14]
The competing MGBASE-T Alliance, stating the same faster Gigabit Ethernet objectives, was founded in December 2014.
[15]
In contrast to NBASE-T, the MGBASE-T said that their specifications would be open source.
[16]
IEEE 802.3
's "2.5G/5GBASE-T Task Force" started working on the 2.5GBASE-T and 5GBASE-T standards in March 2015.
[17]
The two NBASE-T and MGBASE-T Alliances ended up collaborating.
[18]
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.
[19]
Automotive Ethernet standards
[
edit
]
The IEEE 802.3ch-2020 2.5GBASE-T1, 5GBASE-T1, and 10GBASE-T1 standards are derived from the IEEE 802.3bp-2016
1000BASE-T1
Ethernet over single twisted pair
standard, and share very little in common with the similarly named 2.5GBASE-T and 5GBASE-T standards at the PHY layer. 2.5GBASE-T1, 5GBASE-T1, and 10GBASE-T1 can run over a single twisted pair up to 15 meters in length, use PAM8 modulation (compared to PAM3 modulation in 1000BASE-T1 or PAM-16 + 128DSQ in 2.5GBASE-T/5GBASE-T), and are standardized in 802.3ch-2020.
[20]
Their primary use is in embedded automotive applications, and are commonly referred to as part of the Automotive Ethernet family of standards, along with
100BASE-T1
and
1000BASE-T1
.
See also
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]
References
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]
External links
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]
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