Key Terms Chapter 4

modem

A device that converts binary signals into audio signals for transmission over standard voice-grade telephone lines and converts the audio signals back into binary.

signal-to-noise ratio

A measure of the quality of a communication channel.

repeater

A network device used to amplify signals on long cables between nodes.

token ring

A LAN technology that has stations wired in a ring, in which each station constantly passes a special message token on to the next; whichever station has the token can send the message.

network interface card (NIC)

A circuit board that connects a network medium to the system bus and converts a computer's binary information into a format suitable for the transmission medium; each NIC has a unique, 48-bit address.

ISO OSI reference model

A data communication model consisting of seven functional layers.

PDU (protocol data unit)

A data communication packet containing protocol information in addition to a data payload.

T1 line

A digital transmission link with a capacity of 1.544 mbps; T1 uses two pairs of normal twisted wires, the same twisted wires used in most homes.

802.11

A family of specifications for WLANS developed by the IEEE, currently includes 802.11, 802.11a, 802.11b, 802.11g, and 802.11n.

100BaseT

A fast Ethernet networking cable made up of four twisted pairs of wire and capable of transmitting at 100 Mbps.

WLAN (wireless LAN)

A local network that uses wireless transmission instead of wires; the IEEE 802.11 protocol family is often used in WLANs.

bandwidth

A measurement of how much information can be carried in a given time period over a wired or wireless communication medium, usually measured in bits per second (bps).

DSL (digital subscriber line)

A method of sending and receiving data over regular phone lines, using a combination of FDM and TDM.

gateway

A network component, similar to a bridge, that allows connecting networks of different types.

firewall

A network device that protects a network by filtering out potentially harmful incoming and outgoing traffic.

LAN (local area network)

A network of computers in a single building or close proximity.

switch

A network repeater with multiple inputs and outputs, each input can be switched to any of the outputs, creating a point-to-point circuit.

ATM (Asynchronous Transfer Mode)

A network technology based on transferring data in cells or packets of a fixed size at speeds up to 2,488 Gbps.

hub

A networking device that functions as a multiport repeater; signals received on any port are immediately retransmitted to an other port on the hub.

datagram

A packet of information used in a connectionless network service that's routed to its destination by using an address included in the datagrams header.

twisted pair

A pair (sometimes pairs) of insulated wires twisted together and used as a transmission medium in networking.

attenuation

A reduction in the strength of an electrical signal as it travel's along a medium.

network topology

A schematic description of the arrangement of a network, including its nodes and connecting lines.

protocol

A set of rules designed to facilitate communication; protocols are heavily used in networking.

bridge

A special type of network switch that can be configured to allow only specific network traffic through, based on the destination address.

CCITT (Comile Consultatif International Telephonique et Telegrahique)

A standards group involved in the development of the ISO OSI reference model.

TDM (time-division multiplexing)

A technique for combining many signals on a single circuit by allocating each signal a fixed amount of time but allowing each signal the full bandwidth during the allotted time.

FDM (Frequency division multiplexing)

A technique for combining many signals on a single circuit by dividing available transmission bandwidth by frequency into narrower bands, each used for a separate communication channel.

FM (frequency modulation)

A technique of placing data on an alternating carrier wave by varying the signal's frequency; this technique is often used in modems.

PM (phase modulation)

A technique of placing data on an alternating carrier wave by varying the signal's phase; the most common modulation in modems.

AM (amplitude modulation)

A technique of placing data on an alternating carrier wave by varying the signals amplitude, this technique is often used in modems.

FDDI (Fiber Distributed Data Interface) -

A token passing, fiber-optic cable protocol with support for data rates up to 100 Mbps, FDDI networks are typically used as the main lines for WANS.

10BaseT

A twisted pair Ethernet networking cable capable of transmitting at rates up to 10 Mbps (mega bites per second).

cable modem

A type of digital modem that connects to a local cable TV line to provide a continuous connection to the internet.

IEEE (Institute of Electrical and Electronics Engineers)

An organization involved in formulating networking standards.

ISO (International Organization for Standardization)

An organization that coordinates worldwide standards and development.

node

Any addressable device attached to a network that can recognize, process, or forward data transmissions on.

coaxil

Communication cable that consists of a center wire surrounded by insulation and then grounded foil shield wrapped in steel copper braid.

guided media

Physical transmission media, such as wire or cable.

Ethernet

a common method of networking computers in a LAN, using copper cabling at speeds up to 100 Mbps.

transmission medium

a material with the capability to conduct electricity and/or electromagnetic signals.

cat 5

a popular Ethernet twisted pair communication cable capable of carrying data rates up to 100 mbps.

Bluetooth

a specification for short-range RF links between mobile computers, mobile phones, digital cameras, and other portable devices.

Fiber-optic

guided network cable consisting of bundles of thin glass strands surrounded by a protective plastic sheath.

WAN (wide area network)

networks in which computer devices are physically distant from each other, typically spanning cities, states, or even continents.

inductance

the magnetic field around a conductor that opposes changes in current flow.

10GBaseT

The fastest Ethernet networking cable, capable of transmitting at 10 Gbps (gigabits per second) over twisted pairs of wires.

impedance

The opposition a transmission medium has toward the flow of alternating electrical currents.

bit error rate

The percentage of bits that have errors in relation to the total number of bit received in a transmission; a measure of the quality of a communication line.

unguided media

Transmission media you can't see; such as air or space, that carries radio or light signals.