Management information system ralp 7e ch06

Principles of Information Systems, Seventh Edition 3• An unmistakable trend of communications technology is that more people are able to send and receive all forms of information over g

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Principles of Information Systems, Seventh Edition 2

• Effective communications are essential to organizational

success

• Define the terms communications and telecommunications

and describe the components of a telecommunications

system

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• An unmistakable trend of communications technology is

that more people are able to send and receive all forms of information over greater distances at a faster rate

• Identify broad categories of communications media and

discuss the basic characteristics of specific media types

• Describe how a modem works

• Explain the types of telecommunications carriers today and

the services they provide

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• Identify the benefits associated with a telecommunications

network

• Define the term network topology and identify five

alternatives

• Discuss the different communications protocols and

devices used for telecommunications

• Name three distributed processing alternatives and discuss

their basic features

• List some telecommunications applications that

organizations are benefiting from today

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An Overview Of Communications

Systems

• Communications: the transmission of a signal by way of

a medium from a sender to a receiver

• Signal contains a message composed of data and

information

• In telecommunications, sender transmits a signal through

a transmission medium such as a cable

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Figure 6.2: Communications and

Telecommunications

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An Overview Of Communications

Systems (continued)

• Communications can be synchronous or asynchronous

• Synchronous communications: the receiver gets the

message instantaneously

• Asynchronous communications: the receiver gets the

message some period of time after it is sent

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Telecommunications

• Telecommunications: electronic transmission of signals

for communications, via telephone, radio, television, etc

• Data communications: subset of telecommunications that

refers to the electronic collection, processing, and

distribution of data, typically between computer system hardware devices

• Telecommunications medium: anything that carries an

electronic signal and interfaces between a sending device and a receiving device

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Figure 6.3: Elements of a Telecommunications System

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Communications Channels: Basic

Communications Channel

Characteristics

• Communication channels can be classified as simplex,

half-duplex, or full-duplex

• Simplex channel: can transmit data in only one direction

• Half-duplex channel: can transmit data in either direction,

but not simultaneously

• Full-duplex channel: permits data transmission in both

directions at the same time

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Channel Bandwidth and

Information-Carrying Capacity

• Bandwidth: the range of frequencies that an electronic

signal occupies on a given transmission medium

• Shannon’s fundamental law of information theory:

states that the information-carrying capacity of a channel

is directly proportional to its bandwidth

• Broadband: telecommunications in which a wide band

of frequencies is available to transmit information

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Types of Media

• Guided transmission media: communications signals are

guided along a solid medium

• Wireless media: communications signals are sent over

airwaves

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Table 6.1: Transmission Media Types

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Table 6.1: Transmission Media Types

(continued)

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Modems

• A typical telephone line can only accommodate an analog

signal (a continuous, curving signal)

• A computer generates a digital signal representing bits

• Modem: a device that translates data from digital to

analog and analog to digital

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Figure 6.8: How a Modem Works

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Multiplexers

• Multiplexers: devices that allow several

telecommunications signals to be transmitted over a single communications medium at the same time

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Figure 6.9: Use of a Multiplexer to

Consolidate Data Communications onto

a Single Communications Link

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Front-End Processors

• Front-end processors: special-purpose computers that

manage communications to and from a computer system

• Connect a midrange or mainframe computer to hundreds

or thousands of communications lines

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Figure 6.10: Front-End Processor

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Carriers and Services

• Local exchange carrier (LEC): a public telephone

company in the United States that provides service to

homes and businesses within its defined geographical area

• Competitive local exchange carrier (CLEC): a company

that is allowed to compete with the LECs, such as a

wireless, satellite, or cable service provider

• Long-distance carrier: a traditional long-distance phone

provider, such as AT&T, Sprint, or MCI

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Switched and Dedicated Lines

• Switched line: a communications line that uses switching

equipment to allow one transmission device to be

connected to other transmission devices

• Dedicated line: a communications line that provides a

constant connection between two points; also called a

leased line

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Voice and Data Convergence

• Voice over Internet protocol (VoIP): the basic transport

of voice in the form of a data packet using the Internet protocol

• IP telephony is the technology for transmitting voice

communications over a network using an open based Internet protocol

standards-• Voice and data convergence: the integration of voice

and data applications in a common environment

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WATS

• Wide-area telephone service (WATS): a fixed-rate

long-distance telecommunications service for heavy users of voice services

• IN-WATS service

• OUT-WATS service

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ISDN

• Integrated services digital network (ISDN): a set of

standards for integrating voice and data communications onto a single line via digital transmission over copper wire

or other media

• ISDN requires special adapters at both ends of the

transmission line

• ISDN Basic Rate Interface

• ISDN Primary Rate Interface

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Figure 6.12: ISDN Network Switching

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T-Carrier System

• Introduced in the 1960s to support digitized voice

transmission

• Uses four wires and provides duplex capability

• T-1 carrier is capable of carrying 1.544 Mbps over copper

wire; commonly used in U.S., Japan, and Canada

• T-3 line is capable of transmitting data at a rate of

44.736 Mbps

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Digital Subscriber Line (DSL)

• Digital subscriber line (DSL): a telecommunications

technology that delivers high-bandwidth information to homes and small businesses over ordinary copper

telephone wires

• Provides a transmission rate of 512 Kbps to 1.544 Mbps

from the central office to the subscriber

• Provides a transmission rate of about 128 Kbps from the

subscriber to the central office

• Can carry both data and voice signals

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Wireless Mobile

Table 6.3: Some Wireless Data Communications Options

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Networks

• Computer network: the communications media, devices,

and software needed to connect two or more computer

systems and/or devices

• Network nodes: the computers and devices on the

networks

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Network Types

• Personal area network (PAN)

• Local area network (LAN)

• Metropolitan area network (MAN)

• Wide area network (WAN)

• International network

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Network Topology

• Network topology: logical model that describes how

networks are structured or configured

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Figure 6.15: The Basic Network

Topologies

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Terminal-to-Host, File Server, and

Client/Server Systems

• Classifications based on how computers on the network

connect and interoperate

• Terminal-to-host: application and database reside on one

host computer, and the user interacts with application and data using a “dumb” terminal

• File server: the application and database reside on one

host computer (file server)

• Client/server: multiple computer platforms are dedicated

to special functions such as database management,

printing, communications, and program execution

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Figure 6.18: Client/Server Connection

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Interconnecting Networks:

Communications Protocols

• Open Systems Interconnection (OSI) model

• Transmission Control Protocol/Internet Protocol (TCP/IP)

• Systems Network Architecture (SNA)

• IEEE 802.3 (Ethernet)

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Communications Protocols (continued)

• Frame Relay

• Asynchronous Transfer Mode (ATM)

• FireWire

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Wireless Communications Protocols

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Wireless Communications Protocols

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Network Switching Devices

switching system owned or leased by a private enterprise that interconnects its telephones and provides access to the public telephone system

that use the same communications protocol

data from any one of many ports to a specific output port that will take the data toward its intended destination

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Network Switching Devices (continued)

• Router: a device or software in a computer that

determines the next network point to which a data packet should be forwarded toward its destination

• Hub: a place of convergence where data arrives from one

or more directions and is forwarded out in one or more other directions

• Gateway: a network point that acts as an entrance to

another network

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Network Basics: Basic Processing

Strategies

• Centralized processing: all processing occurs in a single

location or facility

• Decentralized processing: processing devices are placed

at various remote locations

• Distributed processing: computers are placed at remote

locations but connected to each other via a network

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Communications Software

• Network operating system (NOS): systems software

that controls the computer systems and devices on a

network and allows them to communicate with each other

• Network-management software: enables a manager on

a networked desktop to monitor the use of individual

computers and shared hardware, scan for viruses, and

ensure compliance with software licenses

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Telecommunications Applications

• Linking personal computers to mainframes and networks

• Voice mail

• Electronic software distribution

• Electronic document distribution

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Telecommunications Applications

(continued)

• Public network services

• Electronic funds transfer (EFT)

• Distance learning

• Specialized systems and services

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Summary

• Communications: the transmission of a signal by way of

a medium from a sender to a receiver

• In telecommunications, the sender transmits a signal

through a transmission medium such as a cable

• Transmission media types: twisted-pair wire cable,

coaxial cable, fiber-optic cable, microwave, cellular, and infrared

• Telecommunications carriers can be divided into local

exchange carriers, competitive local exchange carriers, and long-distance carriers

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Summary (continued)

• A computer network consists of the communications

media, devices, and software needed to connect two or more computer systems and/or devices

• Network types: personal area network (PAN), local area

network (LAN), metropolitan area network (MAN), wide area network (WAN), and international network

• Network topologies: ring, bus, hierarchical, star, and

hybrid

• Options for how computers on a network connect:

terminal-to-host, file server, and client/server

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Summary (continued)

• Communications protocols include the Open Systems

Interconnection (OSI) model, Transmission Control

Protocol/Internet Protocol (TCP/IP), IEEE 802.3

(Ethernet), etc

• Network switching devices: private branch exchange

(PBX), bridge, switch, router, hub, and gateway

• Examples of telecommunications applications are voice

mail, electronic software distribution, telecommuting,

videoconferencing, electronic funds transfer, and distance learning

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