ARCHIVED: What are some common networking terms?

In its most basic form, a computer network consists of two or more computers linked together, usually by cables, so that data can pass between them. The material used to link the computers is called the media. The various communications standards that allow computers to communicate with each other across a network are known as protocols.

The most common forms of media are telephone lines, twisted-pair cable, coaxial (coax) cable, and fiber-optic cable. Others include infrared light, radio waves, and additional wireless communication equipment.

• Telephone lines
• Twisted-pair cables
• Coaxial cable
• Fiber Distributed Data Interface
• SONET
• Wireless media
• T-1 and T-3 dedicated digital lines
• Integrated Services Digital Network
• Digital Subscriber Line
• Ethernet
• Asynchronous Transfer Mode
• Frame relay

Telephone lines

Telephone lines, although not designed for computer networking, are the most common method of linking remote computers to computer networks. If your computer has a modem, you can use your telephone line to connect to any other computer with a modem. The advantages of telephone lines are that they are widely available, don't require special network cables, have unlimited range, and (unless you're dialing long distance) are inexpensive to use. The disadvantage of telephone lines is that they transfer data slowly.

In theory, data transmitted along a telephone line can reach a speed of 53.3Kbps (kilobits per second). Due to line noise, wire properties, and power constraints, most modem connections are limited to 33Kbps or less. This slow transfer speed keeps them from being commonly used for computer networks. However, some experimental networking technologies use the phone lines of your house to link several computers into a household network.

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Twisted-pair cables

Twisted-pair cables are used for most Ethernet local area networks (LANs). Each cable consists of one or more pairs of wire twisted together to limit electromagnetic interference. Ethernet with a speed of 10Mbps (megabits per second) actually uses two pairs of wire; faster speeds use four pairs. Each pair is twisted independently of the others.

Twisted-pair cables fall into two categories: unshielded twisted pair (UTP) and shielded twisted pair (STP). UTP cables are cheap and flexible. They can send a signal up to 100 meters without needing a repeater. Their main drawback is that they are susceptible to electromagnetic interference. STP cables are less common. They are almost identical to UTP, but they have a layer of wire mesh shielding around the wires. While this blocks electromagnetic noise, it also makes this type of cabling more expensive.

All forms of twisted-pair cable can transmit information at varying rates of speed, depending on their type. The standards for twisted-pair cable divide them into five different categories, labeled CAT1 through CAT5. Of these five types, the most commonly used are CAT3 and CAT5.

CAT3 can handle speeds up to 10Mbps. The IEEE 802.3 Ethernet 10BaseTX network standard can work with CAT3 cabling. IEEE CAT5 also meets the 802.3 specification, and can transmit data at speeds of up to 100Mbps. It is commonly used for 100BaseTX (Fast Ethernet over copper) networks. A 1000BaseTX (1Gbps) network can also run using CAT5 cable.

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Coaxial cable

Coaxial networking cable is similar to cabling used for cable TV connections. It consists of a solid copper core covered with a metal shield to block electromagnetic interference. Typically, coaxial cable is used to carry voice, video, and data over the same wire. Two main types of coaxial cable are used in computer networking: thinnet (RG-58) and thicknet (RG-8 or RG-11).

Thinnet cable can transmit 10Mbps up to 185 meters. Wire segments of thinnet are connected with BNC connectors. Thinnet coaxial cables are commonly used for 10Base2 Ethernet networks.

Thicknet cable can transmit data at the same rate as thinnet cable for up to 500 meters. To connect to each computer's network card, thicknet uses a "vampire tap", (also called a Media Access Unit, or MAU), which physically punctures the wire, and a cable called the Attachment Unit Interface (AUI). The AUI runs between the MAU and the computer's network interface card (NIC).

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Fiber Distributed Data Interface

Fiber Distributed Data Interface (FDDI) uses fiber-optic cable for computer networking. Fiber-optic media consists of a glass or plastic core, covered by a glass or plastic cladding, which is in turn surrounded by an outer cover. Lasers or light-emitting diodes (LEDs) transmit one-way light signals through these cables for up to 100 kilometers. Cables are made up of two strands; each strand transmits data in one direction. Data transfer speeds from 100Mbps to 2Gbps (gigabytes per second) are possible. Because FDDI networks consist of dual fiber rings, they tend to be more fault tolerant than some other network configurations. However, they also tend to be more expensive.

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SONET

Synchronous Optical Network (SONET) is a new protocol for transmitting digital signals on optical fiber. The base rate (OC-1) is 51.84Mbps. OC-2 runs at twice the base rate, OC-3 at three times the base rate, and so on. Currently planned rates include OC-1, OC-3 (155.52Mbps), OC-12 (622.08Mbps), and OC-48 (2.488Gbps). ATM makes use of some of the Optical Carrier levels. This networking protocol is also called STS-x or OC-x. Indiana University's Abilene (Internet2) system consists of a network backbone made from OC-48 and OC-12 fiber connections.

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Wireless media

There are a variety of wireless network media, each of which uses a different transmission protocol. Typically, a wireless network uses infrared light or radio transmissions to distribute data.

• Infrared networks communicate by using beams of infrared light. They have a maximum range of 100 meters. Theoretically, they can transmit at 10Mbps, but 1-3Mbps is more typical.
• Narrow-band radio networks can cover an area up to 5,000 square meters at up to 4.8Mbps. Their disadvantage is that they offer little security.
• Spread-spectrum radio networks use multiple frequencies. These multiple channels provide network security. They can transmit data at up to 1Mbps at a range of 800 feet indoors, though 300Kbps is more typical.

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T-1 and T-3 dedicated digital lines

T1 and T3 lines are point-to-point dedicated data transmission lines that provide data transfer rates of 1.544Mbps and 45Mbps, respectively. A T1 line consists of 24 channels, each of which operate at a speed of 64Kbps. A T3 line is composed of 28 T1 lines.

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Integrated Services Digital Network

Integrated Services Digital Network (ISDN) is fully digital telephone service, providing data, voice, and video channels over the existing phone network. Most of the existing telephone network is digital. The exception is the part that connects the local exchange with individual houses or offices. ISDN makes the entire service digital.

ISDN service is generally obtained from a telephone company and Internet service provider. There are two different classes of ISDN: Basic Rate Interface (BRI) and Primary Rate Interface (PRI):

• Basic ISDN (BRI) is intended to meet the needs of most individual users and small networks. It is fairly inexpensive and uses existing phone wiring. It divides the telephone line into three channels: two 64Kbps bearer channels, or "B channels", and one 16Kbps "D channel" for setting up and managing calls. In some situations, the two bearer channels can function together as a single virtual channel, with a data transmission speed of 128Kbps.
• Primary ISDN (PRI) is intended for organizations with greater capacity requirements. It uses a full T1 line, transmitting at 1.544Mbps. It has 23 bearer channels that each operate at 64Kbps, and one 64Kbps setup channel.

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Digital Subscriber Line

Digital Subscriber Line (DSL) also uses existing phone wiring. DSL is similar to ISDN, but it provides speeds up to 1.5Mbps; however, the speed and availability of DSL are limited by the customer's distance from the local telephone switch.

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Ethernet

Ethernet is probably the most common form of computer network. It typically consists of 10BaseT twisted-pair cables and NICs optimized to use the IEEE 802.3 Ethernet standard. A similar standard, called Fast Ethernet, uses 100BaseT twisted-pair cable. Most of the networks at Indiana University Bloomington, including those in the residence halls and the Student Technology Centers, use the Ethernet protocol.

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Asynchronous Transfer Mode

Asynchronous Transfer Mode (ATM) networks transmit data over wide-area networks (WANs) and LANs in fixed 53 byte "cells". Theoretical transmission speed is 1.2Gbps, but 155 or 622Mbps are more typical. These networks are very expensive, but are commonly used for "backbones" of large computer networks. For example, the backbone at IUPUI is all ATM.

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Frame relay

This network protocol is derived from X.25 and ISDN, and provides little error checking. It relies on the quality of network connections and Permanent Virtual Circuits (PVC) between end points of the network. Speeds from 56Kbps up to 45Mbps are possible. Frame relay networks cost less than ATM connections or dedicated data lines.

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