ETHERNET OVER TWISTED PAIR technologies use twisted-pair cables for
the physical layer of an
Ethernet computer network.
Ethernet had used various grades of coaxial cable , but in
StarLAN showed the potential of simple unshielded twisted pair .
This led to the development of
10BASE-T and its successors 100BASE-TX
1000BASE-T , supporting speeds of 10, 100 and 1,000 Mbit/s
All these three standards define 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
consequently define only full-duplex point-to-point links which are
generally connected by network switches , and don't support the
All these standards use
8P8C connectors, and the cables from Cat3
to Cat8 have four pairs of wires; though
use two of the pairs.
* 1 History
* 2 Naming
* 3 Cabling
* 3.1 Shared cable
* 3.2 Single-pair
Autonegotiation and duplex mismatch
* 5 Variants
* 6 See also
* 7 Notes
* 8 References
* 9 Further reading
* 10 External links
Institute of Electrical and Electronics Engineers (IEEE)
standards association ratified several versions of the technology. The
first two early designs were
StarLAN , standardized in 1986, at one
megabit per second, and
LattisNet , developed in January 1987, at 10
megabit per second. Both were developed before the
(published in 1990 as
IEEE 802.3i ) and used different signalling, so
they were not directly compatible with it.
In 1988 AT">
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 the standard includes auto MDI-X; however, implementation is
optional. With the way that
1000BASE-T implements 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 and also specify a maximum cable length of 100
Category 5 cable has since been deprecated and new
Ethernet standards using broadband and coaxial cable ,
10BASE5 (thicknet ) and
10BASE2 (thinnet ),
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
Category 5 cable § Shared cable
100BASE-TX only require two pairs (pins 1–2, 3–6) to
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. Moreover, 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 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 (link segment type A) or up to 40 m with up to
four in-line connectors.
AUTONEGOTIATION AND DUPLEX MISMATCH
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 of operation.
1000BASE-T requires autonegotiation to be on in
order to operate.
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
Category 3 cable. An active hub sits in the middle and has a port
for each node. Manchester coded signaling.
Runs over AT">
* ^ 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
* ^ The
8P8C modular connector is often called RJ45 after a
telephone industry standard .
* ^ The same simple cable used for telephone systems .
* ^ Transfer speed = channels × bits per hertz × spectral
* ^ On
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
Manchester code , and
100BASE-TX where it is one quarter because
MLT-3 encoding .
* ^ 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 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.
25-pair color code
Copper cable certification