Ethernet over twisted pair technologies use twisted-pair cables for
the physical layer of an
Ethernet computer network. They are a subset
Ethernet physical layers.
Ethernet had used various grades of coaxial cable, but in 1984,
StarLAN showed the potential of simple unshielded twisted pair. This
led to the development of
10BASE-T and its successors 100BASE-TX,
1000BASE-T and 10GBASE-T, supporting speeds of 10, 100
1 and 10
All these standards use
8P8C connectors,[b] and the cables from Cat 3
to Cat 8.[c]
3.1 Shared cable
Autonegotiation and duplex
6 See also
9 Further reading
10 External links
The first two early designs of twisted pair networking were StarLAN,
standardized by the
IEEE Standards Association as
IEEE 802.3e in 1986,
at one megabit per second, and LattisNet, developed in January
1987, at 10 megabit per second. Both were developed before the
10BASE-T standard (published in 1990 as
IEEE 802.3i) and used
different signalling, so they were not directly compatible with it.
In 1988 AT&T released StarLAN 10, named for working at
10 Mbit/s. The StarLAN 10 signalling was used as the
basis of 10BASE-T, with the addition of link beat to quickly indicate
Using twisted pair cabling, in a star topology, for
several weaknesses of the previous standards:
Twisted pair cables were already in use for telephone service and were
already present in many office buildings, lowering overall cost
The centralized star topology already in use for telephone service and
was a more common approach to cabling than the bus in earlier
standards and easier to manage
Using point-to-point links was less prone to failure and greatly
simplified troubleshooting compared to a shared bus
Exchanging cheap repeater hubs for more advanced switching hubs
provided a viable upgrade path
Mixing different speeds in a single network became possible with the
arrival of Fast Ethernet
Depending on cable grades, subsequent upgrading to Gigabit
faster could be accomplished by replacing the network switches
10BASE-T is rarely used as a normal-operation signaling rate
today, it is still in wide use with NICs in
mode and for special, low-power, low-bandwidth applications. 10BASE-T
is still supported on practically any twisted-pair port with up to
Ethernet physical layer § Physical layers
The common names for the standards derive from aspects of the physical
media. The leading number (10 in 10BASE-T) refers to the transmission
speed in Mbit/s. BASE denotes that baseband transmission is used. The
T designates twisted pair cable, where the pair of wires for each
signal is twisted together to reduce electromagnetic interference and
crosstalk between pairs. Where there are several standards for the
same transmission speed, they are distinguished by a letter or digit
following the T, such as TX, referring to the encoding method and
number of lanes.
8P8C modular plug pin positioning
TIA/EIA-568 T568A termination
TIA/EIA-568 T568B termination
Ethernet standards are such that the majority of cables
can be wired "straight-through" (pin 1 to pin 1, pin 2 to pin 2 and so
on), but others may need to be wired in the "crossover" form (receive
to transmit and transmit to receive).
It is conventional to wire cables for 10- or 100-
either the T568A or T568B standards. Since these standards differ only
in that they swap the positions of the two pairs used for transmitting
and receiving (TX/RX), a cable with T568A wiring at one end and T568B
wiring at the other is referred to as a crossover cable. The terms
used in the explanations of the 568 standards, tip and ring, refer to
older communication technologies, and equate to the positive and
negative parts of the connections.
100BASE-TX node such as a PC uses a connector wiring
called medium dependent interfaces (MDI), transmitting on pin 1 and 2
and receiving on pin 3 and 6 to a network device. An infrastructure
node (a hub or a switch) accordingly uses a connector wiring called
MDI-X, transmitting on pin 3 and 6 and receiving on pin 1 and 2. These
ports are connected using a "straight-through" cable, so each
transmitter talks to the receiver on the other side.
Nodes can have two types of ports: MDI (uplink port) or MDI-X (regular
port, 'X' for internal crossover). Hubs and switches have regular
ports. Routers, servers and end hosts (e.g. personal computers) have
uplink ports. When two nodes having the same type of ports need to be
connected, a crossover cable is often required at speeds of 10 or
100 Mbit/s, else connecting nodes having different type of ports
(i.e. MDI to MDI-X and vice versa) requires straight-through cable.
Thus connecting an end host to a hub or switch requires a
straight-through cable. On switches/hubs sometimes a button is
provided to allow a port to act as either a normal (regular) or an
uplink port, i.e. using MDI-X or MDI pinout respectively.
Ethernet host adapters can automatically detect another
computer connected with a straight-through cable and then
automatically introduce the required crossover, if needed; if neither
of the adapters has this capability, then a crossover cable is
required. Most newer switches have automatic crossover ("auto MDI-X"
or "auto-uplink") on all ports, eliminating the uplink port and the
MDI/MDI-X switch, and allowing all connections to be made with
straight-through cables. If both devices being connected support
1000BASE-T according to the standards, they will connect regardless of
whether a straight-through or crossover cable is used.
10BASE-T transmitter sends two differential voltages, +2.5 V or
100BASE-TX follows the same wiring patterns as 10BASE-T, but is more
sensitive to wire quality and length, due to the higher bit rates.
100BASE-TX transmitter sends three differential voltages, +1 V,
0 V, or −1 V.
1000BASE-T uses all four pairs bi-directionally using hybrid circuits
and cancellers. The standard includes auto MDI-X; however,
implementation is optional. With the way that
signaling, how the cable is wired is immaterial in actual usage. The
standard on copper twisted pair is
Cat 5e UTP, or
4D-PAM5; four dimensions using PAM (pulse amplitude modulation) with
five voltages, −2 V, −1 V, 0 V, +1 V, and
+2 V. While +2 V to −2 V voltage may appear at
the pins of the line driver, the voltage on the cable is nominally
+1 V, +0.5 V, 0 V, −0.5 V and −1 V.
1000BASE-T were both designed to require a minimum of
Category 5 cable
Category 5 cable and also specify a maximum cable length of 100
Category 5 cable
Category 5 cable has since been deprecated and new
Ethernet standards using broadband and coaxial cable,
10BASE5 (thicknet) and
10BASE-T does not
specify the exact type of wiring to be used, but instead specifies
certain characteristics that a cable must meet. This was done in
anticipation of using
10BASE-T in existing twisted-pair wiring systems
that may not conform to any specified wiring standard. Some of the
specified characteristics are attenuation, characteristic impedance,
timing jitter, propagation delay, and several types of noise. Cable
testers are widely available to check these parameters to determine if
a cable can be used with 10BASE-T. These characteristics are expected
to be met by 100 meters of 24-gauge unshielded twisted-pair cable.
However, with high quality cabling, cable runs of 150 meters or longer
are often obtained and are considered viable by most technicians
familiar with the
10BASE-T specification.
Category 5 cable
Category 5 cable § Shared cable
100BASE-TX only require two pairs (pins 1–2, 3–6) to
Category 5 cable
Category 5 cable has four pairs, it is possible, but
not necessarily standards compliant, to use the spare pairs (pins
4–5, 7–8) in 10- and 100-
Mbit/s configurations. The spare pairs
may be used for Power over
Ethernet (PoE), or two phone lines, or a
100BASE-TX connection. In practice, great care must
be taken to separate these pairs as most 10/100-
Mbit/s hubs, switches,
and PCs electrically terminate the unused pins.
1000BASE-T requires all four pairs to operate.
In addition to the more computer-oriented two and four-pair variants,
the 100BASE-T1 and 1000BASE-T1 single-pair
Ethernet PHYs (SPE) are
intended for automotive applications or as optional data channels in
other applications. The single pair operates at full duplex and
has a maximum reach of 15 m (100BASE-T1, 1000BASE-T1 link segment
type A) or up to 40 m (1000BASE-T1 link segment type B) with up
to four in-line connectors. Both PHYs require a balanced twisted pair
with an impedance to 100 Ω. The cable must be capable of
transmitting 600 MHz for 1000BASE-T1 and 66 MHz for
Similar to PoE, Power over Data Lines (PoDL) can provide up to
50 W to a device.
Autonegotiation and duplex
Ethernet over twisted pair standards up to Gigabit
both full-duplex and half-duplex communication. However, half-duplex
operation for gigabit speed isn't supported by any existing
hardware. Higher speed standards,
2.5GBASE-T up to
40GBASE-T running at 2.5 to 40 Gbit/s, consequently define
only full-duplex point-to-point links which are generally connected by
network switches, and don't support the traditional shared-medium
Many different modes of operations (
10BASE-T half duplex, 10BASE-T
100BASE-TX half duplex, ...) exist for
twisted pair, and most network adapters are capable of different modes
1000BASE-T requires autonegotiation to be on in order to
When two linked interfaces are set to different duplex modes, the
effect of this duplex mismatch is a network that functions much more
slowly than its nominal speed.
Duplex mismatch may be inadvertently
caused when an administrator configures an interface to a fixed mode
Mbit/s full duplex) and fails to configure the remote
interface, leaving it set to autonegotiate. Then, when the
autonegotiation process fails, half duplex is assumed by the
autonegotiating side of the link.
Runs over four wires (two twisted pairs) on telephone twisted pair or
Category 3 cable. An active hub sits in the middle and has a port for
each node. Manchester coded signaling.
Runs over AT&T Premises Distribution System (PDS) wiring or four
wires (two twisted pairs) on telephone twisted pair or
Runs over four wires (two twisted pairs) on a
Category 3 or
Star topology with an active hub or switch sits in the middle
and has a port for each node. This is also the configuration used for
100BASE-T and Gigabit Ethernet. Manchester coded signaling.
MLT-3 coded signaling,
Category 5 cable
Category 5 cable copper cabling with two
PAM-5 coded signaling. At least
Category 5 cable
Category 5 cable with four twisted
pairs copper cabling.
Category 5 cable
Category 5 cable has since been deprecated and
new installations use
Category 5e. Each pair is used in both
Category 5e (2.5G) and
Category 6 (5G)
THP PAM-16 coding. Uses category 6a cable.
10GBASE-T for proposed Cat 8.1/8.2 shielded cable
Cat 8 (30 m)
Cat 8 (30 m)
^ Transfer speed = channels × bits per hertz × spectral bandwidth
100BASE-TX one twisted pair of the cabling is used
for transmission and another for reception, leaving two unused pairs.
Higher speeds use all four pairs simultaneously for transmission (TX)
and reception (RX).
^ Effective bits per hertz after loss to encoding overhead.
^ The spectral bandwidth is the maximum rate at which the signal will
complete one hertz cycle. It is typical half the symbol rate, because
one can send a symbol both at the positive and negative peak of the
cycle. Exceptions are
10BASE-T where it is equal because it uses
Manchester code, and
100BASE-TX where it is one quarter because it
^ At shorter cable length, it is possible to use cables of a lower
grade than that is required for 100 m. For example it is possible to
10GBASE-T on a
Cat 6 cable of 55 m or less. Likewise
expected to work with
Cat 5e in most use cases.
25-pair color code
Copper cable certification
^ Generally, the higher-speed implementations support the lower-speed
standards making it possible to mix different generations of
equipment; with the inclusive capability designated 10/100 or
10/100/1000 for connections that support such combinations.:123
8P8C modular connector is often called RJ45 after a telephone
^ These cables typically have four pairs of wires though
100BASE-TX only use two of the pairs.
^ By switching link beat on or off, a number of network interface
cards at the time could work with either
StarLAN 10 or 10BASE-T.
^ Charles E. Spurgeon (2000). Ethernet: the definitive guide. OReilly
Media. ISBN 978-1-56592-660-8.
^ Urs von Burg (2001). The triumph of Ethernet: technological
communities and the battle for the LAN standard. Stanford University
Press. pp. 175–176, 255–256.
^ a b Paula Musich (August 3, 1987). "User lauds SynOptic system:
LattisNet a success on PDS". Network World. 4 (31). pp. 2, 39.
Retrieved June 10, 2011.
^ W.C. Wise, Ph.D. (March 1989). "Yesterday, somebody asked me what I
think about LattisNet. Here's what I told him in a nutshell". CIO
Magazine. 2 (6). p. 13. Retrieved June 11, 2011.
^ Network Maintenance and Troubleshooting Guide. Fluke Networks. 2002.
p. B-4. ISBN 1-58713-800-X.
StarLAN Technology Report, 4th Edition. Architecture Technology
Corporation. 1991. ISBN 9781483285054.
^ Ohland, Louis. "3Com 3C523". Walsh Computer Technology. Retrieved 1
IEEE 802.3 1.2.3 Physical Layer and media notation
IEEE 802.3 40.1.4 Signaling
^ David A. Weston (2001). Electromagnetic Compatibility: principles
and applications. CRC Press. pp. 240–242.
ISBN 0-8247-8889-3. Retrieved June 11, 2011.
IEEE 802.3 40.1.3 Operation of 1000BASE-T
^ Steve Prior. "
1000BASE-T Duffer's Guide to Basics and Startup"
(PDF). Retrieved 2011-02-18.
^ Nick van Bavel, Phil Callahan and John Chiang (2004-10-25).
"Voltage-mode line drivers save on power". Retrieved 2011-02-18.
IEEE 802.3bw Clause 96 and 802.3bp Clause 97
IEEE 802.3bu-2016 104. Power over Data Lines (PoDL) of Single
Balanced Twisted-Pair Ethernet
^ Seifert, Rich (1998). "10". Gigabit Ethernet: Technology and
Applications for High-Speed LANs. Addison Wesley.
^ "Configuring and Troubleshooting
Ethernet 10/100/1000Mb Half/Full
Duplex Auto-Negotiation". Cisco. 2009-10-28. Retrieved
^ a b "
40GBASE-T Task Force".
^ Michael Palmer (2012-06-21). Hands-On Networking Fundamentals, 2nd
ed. Cengage Learning. p. 180. ISBN 978-1-285-40275-8.
^ 802.3a,b,c, and e-1988
IEEE Standards for Local Area Networks:
Supplements to Carrier Sense Multiple Access With Collision Detection
(CSMA/CD) Access Method and Physical Layer Specifications. IEEE
Standards Association. 1987. doi:10.1109/IEEESTD.1987.78883.
^ Eric Killorin (November 2, 1987). "
LattisNet makes the grade in
Novell benchmark tests". 4 (44). Network World. p. 19. Retrieved
March 18, 2011.
IEEE Computer Society (2008-12-26),
IEEE Std 802.3-2008 :
22.214.171.124 Twisted-pair media, IEEE
IEEE 802.3 standards documents
Ethernet Auto Standard Leaves LVDS Cables in the Dust
How to Make a Network Cable, a how-to article from wikiHow
How to create your own
How to wire a 10Base-T or 100Base-T connector with category 5 cable
8P8C modular connectors
Step by step instructions on how to punch down category 5e cable to a
How to make a crossover patch cable using Cat5e or Cat6 and RJ45
Ethernet family of local area network technologies
2.5 and 5 Gbit/s
25 and 50 Gbit/s
40 and 100 Gbit/s
200 and 400 Gbit/s
Power over Ethernet