NetEss7EdChapter04

extended LANs

A LAN that's expanded beyond its normal distance limitations with wireless communication.

twisted-pair (TP) cable

A cable containing one or more pairs of insulated strands of copper wire twisted around one another and housed in an outer sheath.

fiber-optic cable

A cable type that carries data over thin strands of glass by using optical (light) pulses to represent bits.

RJ-45 plug

A connector used to terminate twisted-pair cable for making patch cables. It has eight wire traces to accommodate a standard twisted-pair cable with four wire pairs.

transceiver

A device that transmits and receives. In wireless networking, an access point is a transceiver.

RJ-45 jack

A device used in the work area in wall plates and surface-mounted boxes to plug a patch cable that connects a computer to the horizontal wiring.

electromagnetic interference (EMI)

A disturbance to the operation of an electronic circuit or its data, caused by devices that emit an electromagnetic field.

datagrade

A grade of cable suitable for data networking.

voicegrade

A grade of cable that's not suitable for data networking but is suitable for voice communication.

cable segment

A length of cable between two network devices, such as a NIC and a switch. Any intermediate passive (unpowered) devices, such as wall jacks, are considered part of the total segment length.

differential signal

A method for transmitting data in which two wires of opposite polarity are used. One wire transmits using positive voltage and the other uses negative voltage. Differential signals enhance signal reliability by providing a canceling affect on EMI and crosstalk.

spread-spectrum radio

A radio communication system that uses multiple frequencies simultaneously, thereby improving reliability and reducing susceptibility to interference over narrowband radio.

equipment room

A room that houses servers, routers, switches, and other major network equipment and serves as a connection point for backbone cabling running between telecommunications closets (IDFs). When it's used to connect backbone cabling between buildings and IDFs, it's called a "main distribution frame." See also intermediate distribution frame (IDF) and main distribution frame (MDF).

patch cable

A short cable for connecting a computer to an RJ-45 jack or connecting a patch-panel port to a switch or hub. See also straight-through cable.

structured cabling

A specification for organizing cabling in data and voice networks, regardless of the media type or network architecture.

straight-through cable

A standard patch cable that uses the same wiring standards on both ends so that each wire is in the same location on both ends of the cable (pin 1 goes to pin 1, pin 2 to pin 2, and so forth). See also patch cable.

intermediate distribution frame (IDF)

A telecommunications closet that houses the cabling and devices for work area computers. See also telecommunications closet and work area.

crossover cable

A type of patch cable that uses the 586B standard on one end and the 586A standard on the other end. This arrangement crosses the transmit and receive wires so that transmit on one end connects to receive on the other end. Often used to connect two devices of the same type to one another—for example, connecting a switch to a switch.

hertz (Hz)

A unit expressing how many times per second a signal or electromagnetic wave occurs.

infrared (IR)

A very long wavelength light source in the invisible spectrum that can be used to transmit data wirelessly.

main distribution frame (MDF)

An equipment and cabling room that serves as the connecting point for backbone cabling between buildings and between IDFs; also called the "main cross-connect." See also equipment room.

IrDA devices

Devices that use infrared signals to communicate. IrDA stands for Infrared Device Association.

crosstalk

Interference one wire generates on another wire when both wires are in a bundle.

narrowband radio

Low-powered, two-way radio communication systems, such as those used in taxis, police radios, and other private radio systems; also called "single-frequency radio."

backbone cabling

Network cabling that interconnects telecommunications closets (IDFs) and equipment rooms (MDFs). This cabling (also called "vertical cabling") runs between floors or wings of a building and between buildings to carry network traffic destined for devices outside the work area. It's often fiber-optic cable but can also be UTP.

medium dependent interface (MDI) devices

Network devices that connect by using RJ-45 plugs over twisted-pair cabling; they transmit on pins 1 and 2 and receive on pins 3 and 6 of an RJ-45 connector.

MDI crossed (MDI-X) devices

Network devices that connect by using RJ-45 plugs over twisted-pair cabling; they transmit over pins 3 and 6 and receive over pins 1 and 2 of an RJ-45 connector.

radio frequency interference (RFI)

Similar to EMI, but RFI is usually interference caused by strong broadcast sources. See also electromagnetic interference (EMI).

termination

The attachment of RJ-45 plugs on a cable to make a patch cable or punching down the cable wires into terminal blocks on a jack or patch panel.

cable plant

The collection of all cables and connectors tying a network together.

demarcation point

The location in the cable plant where a connection to a WAN is made and where an organization's LAN equipment ends and a third-party provider's equipment and cabling begins.

entrance facility

The location of cabling and equipment that connects an organization's network to a third-party telecommunications provider. It can also serve as an equipment room and the main cross-connect for all backbone cabling.

work area

The location of workstations and other user devices—in short, the place where people work with computers and other network devices.

encoding

The method used to represent bits on a medium.

horizontal wiring

The network cabling running from the work area's wall jack to the telecommunications closet (IDF), usually terminated at a patch panel. The total maximum distance for horizontal wiring is 100 meters.

telecommunications closet (TC)

Usually an enclosed space or room that provides connectivity to computer equipment in the nearby work area; can also serve as the entrance facility in small installations. Typical equipment includes patch panels to terminate horizontal wiring runs and switches. When it houses the cabling and devices for work area computers, it's called an "intermediate distribution frame." See also intermediate distribution frame (IDF).