Effective communications are essential to organizational success

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


• 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


• 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


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


Figure 6.2: Communications and Telecommunications


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


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


Figure 6.3: Elements of a Telecommunications System


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


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


Types of Media

• Guided transmission media: communications signals are guided along a solid medium

• Wireless media: communications signals are sent over airwaves


Table 6.1: Transmission Media Types


Table 6.1: Transmission Media Types (continued)


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


Figure 6.8: How a Modem Works


Multiplexers

• Multiplexers: devices that allow several telecommunications signals to be transmitted over a single communications medium at the same time


Figure 6.9: Use of a Multiplexer to Consolidate Data Communications onto

a Single Communications Link


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


Figure 6.10: Front-End Processor


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


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


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 standards-based Internet protocol

• Voice and data convergence: the integration of voice and data applications in a common environment


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


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


Figure 6.12: ISDN Network Switching


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


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


Wireless Mobile

Table 6.3: Some Wireless Data Communications Options


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


Network Types

• Personal area network (PAN)

• Local area network (LAN)

• Metropolitan area network (MAN)

• Wide area network (WAN)

• International network


Network Topology

• Network topology: logical model that describes how networks are structured or configured


Figure 6.15: The Basic Network Topologies


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


Figure 6.18: Client/Server Connection


Interconnecting Networks: Communications Protocols

• Open Systems Interconnection (OSI) model

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

• Systems Network Architecture (SNA)

• IEEE 802.3 (Ethernet)


Communications Protocols (continued)

• Frame Relay

• Asynchronous Transfer Mode (ATM)

• FireWire


Wireless Communications Protocols

• Bluetooth

• IEEE 802.11b (Wi-Fi)

• IEEE 802.11g

• IEEE 802.16 (WiMax)

• IEEE 802.20 (MBWA)


Wireless Communications Protocols (continued)

• 1G

• 2G

• 2.5G

• 3G

• Multichannel Multipoint Distribution System (MMDS)


Network Switching Devices

• Private branch exchange (PBX): an on-premise switching system owned or leased by a private enterprise that interconnects its telephones and provides access to the public telephone system

• Bridge: a device used to connect two or more networks that use the same communications protocol

• Switch: a telecommunications device that routes incoming data from any one of many ports to a specific output port that will take the data toward its intended destination


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


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


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


Telecommunications Applications

• Linking personal computers to mainframes and networks

• Voice mail

• Electronic software distribution

• Electronic document distribution


Telecommunications Applications (continued)

• Call centers

• Telecommuting

• Videoconferencing

• Electronic data interchange (EDI)


Telecommunications Applications (continued)

• Public network services

• Electronic funds transfer (EFT)

• Distance learning

• Specialized systems and services


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


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


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

Effective communications are essential to organizational success

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