Ethernet Over Twisted Pair - Wikipedia, The Free Encyclopedia

11/7/2009

Ethernet over twisted pair - Wikipedia, …

Ethernet over twisted pair From Wikipedia, the free encyclopedia

(Redirected from 10BASE-T) Ethernet over twisted pair refers to the use of cables that contain insulated copper wires twisted together in pairs for the physical layer of an Ethernet network—that is, a network in which the Ethernet protocol provides the data link layer. Other Ethernet cable standards use coaxial cable or optical fiber. There are several different standards for this copper-based physical medium. The most widely used are 10BASE-T, 100BASE-TX, and 1000BASE-T (Gigabit Ethernet), running at 10 Mbit/s, 100 Mbit/s (also Mbps or Mbs-1), and 1000 Mbit/s (1 Gbit/s) respectively. These three standards all use the same connectors. Higher speed implementations nearly always support the lower speeds as well, so that in most cases different generations of equipment can be freely mixed. They use 8 position modular connectors, usually called RJ45 in the context of Ethernet over twisted pair. The cables usually used are four-pair twisted pair cable (though 10BASE-T and 10BASE-TX only actually require two of them). Each of the three standards support both full-duplex and halfduplex communication. According to the standards, they all operate over distances of up to 100 meters.

Twisted-pair cable used with 10BASE-T

The common names for the standards derive from aspects of the physical media. The number refers to the theoretical maximum transmission speed in megabits 8P8C plug used with 10BASEper second (Mbit/s). The BASE is short for baseband, meaning that there is no T frequency-division multiplexing (FDM) or other frequency shifting modulation in use; each signal has full control of wire, on a single frequency. The T designates twisted pair cable, where the pair of wires for each signal is twisted together to reduce radio frequency interference and crosstalk between pairs (FEXT and NEXT). Where there are several standards for the same transmission speed, they are distinguished by a letter or digit following the T, such as TX. Some higher-speed standards use coaxial cable, designated by CX.

Contents 1 Cabling 2 Autonegotiation and duplex mismatch 3 See also 4 References 5 External links

Cabling Twisted-pair 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). 10BASE-T and 100BASE-TX only require two pairs to operate, located on pin 1 + 2, and pin 3 + 6. Since 10BASE-T and 100BASE-TX need only two pairs and Category 5 cable has four pairs, it is possible, but not standards compliant, to run two network connections (or a network connection and two phone lines) over a Category 5 cable by using the normally unused pairs (pins 4–5, 7–8) in 10- and 100-Mbit/s configurations. In practice, great care must be taken to separate these pairs as most 10/100-Mbit/s hubs, switches and PCs internally hardwire pins 4–5 together and pins 7–8 together, http://en.wikipedia.org/wiki/10BASE-T

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11/7/2009 Ethernet over twisted pair - Wikipedia, … thereby creating a short-circuit across each "unused" pair. Moreover, 8P8C modular plug pin positioning 1000BASE-T requires all four pairs to operate, pins 1 and 2, 3 and 6 — as well as 4 and 5, 7 and 8. TIA/EIA-568-B T568A Wiring It is conventional to wire cables for 10- or 100-Mbit/s Ethernet to Pin Pair Wire Color either the T568A or T568B standards. Since these standards differ only in that they swap the positions of the two pairs used for 1 3 tip white/green transmitting and receiving (TX/RX), a cable with T568A wiring at one ring green end and T568B wiring at the other is referred to as a crossover cable. 2 3 The terms used in the explanations of the 568 standards, tip and ring, 3 2 tip white/orange refer to older communication technologies, and equate to the positive 4 1 ring blue and negative parts of the connections.

A 10BASE-T or 100BASE-T node such as a PC also called MDI that transmits on pin 1 and 2 and receives on pin 3 and 6 to a network device uses a "straight-through" cable in the MDI wiring pattern. A straight-through cable is usually used to connect a node to its network device. In order for two network devices or two nodes to communicate with each other (such as a switch to another switch or computer to computer) a crossover cable is often required at speeds of 10 or 100 Mbit/s. If available, connections can be made with a straight-through cable by means of an MDI-X port, also known as an "internal crossover" or "embedded crossover" connection. Hub and switch ports with such internal crossovers are usually labelled as such, with "uplink" or "X". For example, 3Com usually labels their ports 1X, 2X, and so on. In some cases a button is provided to allow a port to act as either a normal or an uplink port. To connect two computers directly together without a switch, an Ethernet crossover cable is often used. Although many modern 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 computers have this capability, then a crossover cable is required. If both devices being connected support 1000BASE-T according to the standards, they will connect regardless of the cable being used or how it is wired.

5

1

tip

white/blue

6

2

ring

orange

7

4

tip

white/brown

8

4

ring

brown

TIA/EIA-568-B T568B Wiring Pin Pair Wire

Color

1

2

tip

white/orange

2

2

ring

orange

3

3

tip

white/green

4

1

ring

blue

5

1

tip

white/blue

6

3

ring

green

7

4

tip

white/brown

8

4

ring

brown

To connect two hubs or switches directly together, a crossover cable can be used, but some hubs and switches have an uplink port used to connect network devices together, or have a way to manually select MDI or MDI-X on a single port so that a straight-through cable can connect that port to another switch or hub. 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. A 10BASE-T transmitter sends two differential voltages, +2.5 V or −2.5 V. 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. A 100BASE-TX transmitter sends three differential voltages, +1 V, 0 V, or −1 V[1]. 1000BASE-T uses all four pairs bi-directionally 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 IEEE 802.3ab for 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 [2] 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[3]. Unlike earlier Ethernet standards using broadband and coaxial cable, such as 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 http://en.wikipedia.org/wiki/10BASE-T

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11/7/2009 Ethernet over twisted pair - Wikipedia, … 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, and 100 meters is the stated maximum length for baseband signal runs. 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, though – as with all CSMA/CD network environments – the absolute limit on run length is determined by the size of the collision domain and cable quality. In reality, what meets the standards may not work, and those that do not meet the standards might work.

100BASE-TX and 1000BASE-T were both designed to require a minimum of Category 5 cable and also specify a maximum cable length of 100 meters, though in practice category 5e or above is generally recommended for 1000BASE-T. Furthermore while 10BASE-T is more tolerant of poor wiring such as split pairs, poor terminations and even use of short sections of flat cable, 100BASE-T is less tolerant, and 1000BASE-T is even less so. Since cable testing is often limited to checking if a connection works with Ethernet, running faster speeds over existing cable is often problematic. This problem is made worse by the fact that Ethernet's auto-negotiation takes account only of the capabilities of the end equipment, not of the cable in between.

Autonegotiation and duplex mismatch Main article: Autonegotiation Main article: Duplex mismatch Many different modes of operations (10BASE-T half duplex, 10BASE-T full duplex, 100BASE-TX half duplex, ...) exist for Ethernet over twisted pair, and most network adapters are capable of different modes of operations. In 1995, a standard was released to allow connected network adapters to negotiate the best possible shared mode of operation. The autonegotiation standard contained a mechanism for detecting the speed but not the duplex setting of Ethernet peers that did not use autonegotiation. 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 (e.g. 100 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. The resulting duplex mismatch results in a dramatically slow network, in which many collisions, and especially late collisions occur on the interface set to half-duplex, and FCS errors are seen on the full-duplex side. [4] Gigabit Ethernet standards require autonegotiation to be on in order to operate.

See also 100BaseFX Twisted pair IEEE 802.3 Ethernet physical layer 25-pair color code Computer network Ethernet Fast Ethernet Ethernet extender Network Isolators Power over Ethernet (PoE) Wireless local loop (WLL)

References 1. ^ http://books.google.com/books?id=392CdZHdUDEC&pg=PA240&lpg=PA240&dq=%22100BASETX%22+2V+voltage&source=web&ots=Jtyqtz0KE6&sig=AnR2pHk04YgKKlYAvTiEheQAlHU&hl=en&sa=X&oi=book_result&resnum=8&ct=result 2. ^ http://grouper.ieee.org/groups/802/3/minutes/july98/E2_0798.pdf

http://en.wikipedia.org/wiki/10BASE-T

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Ethernet over twisted pair - Wikipedia, …

3. ^ "Voltage-mode line drivers save on power " (http://www.eetimes.com/showArticle.jhtml?articleID=51200238) 2004 4. ^ Ethernet Autonegotiation Best Practices (http://www.sun.com/blueprints/0704/817-7526.pdf)

External links Download IEEE 802.3 (http://standards.ieee.org/getieee802/802.3.html) Care & Maintenance of Computer Cables (http://static.tigerdirect.com/html/Cable%20Care%20and%20Maintenance.html) Retrieved from "http://en.wikipedia.org/wiki/Ethernet_over_twisted_pair" Categories: Ethernet | Ethernet standards | Ethernet cables | Physical layer protocols | Local loop This page was last modified on 6 November 2009 at 02:05. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of Use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.

http://en.wikipedia.org/wiki/10BASE-T

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