1010-Chapter6

ITEC 1010 Information and Organizations

Chapter 6

Telecommunications and Networks


Communications

Communications The message (data and information) is

communicated via the signal The transmission medium “carries” the signal

Sender ReceiverSignal

Transmissionmedium


Communications ‘Discussion’

The transmission of data from one computer to another, or from one

device to another. A communications device, therefore, is any

machine that assists data transmission. For example, modems,

cables, and ports are all communications devices. Communications

software refers to programs that make it possible to transmit data.


Telecommunications

Telecommunications The electronic transmission of signals for

communications, including such means as:• Telephone

• Radio

• Television

Telecommunication medium• Anything that carries an electronic signal and interfaces

between a sending device and a receiving device


Communications and Telecommunications

• In human speech, the sender transmits a signal through the transmission medium of the air

• In telecommunications, the sender transmits a signal through the transmission medium of a cable

Schematic


Data Communications

Data communications A specialized subset of telecommunications

that refers to the electronic collection, processing, and distribution of data -- typically between computer system hardware devices


Elements of a Telecommunications System

Telecommunication devices Relay signals between computer systems and

transmission media

Schematic


Computer Network

Computer network… The communications media, devices, and

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

Used to share hardware, programs, and databases across the organization

Fosters teamwork, innovative ideas, and new business strategies


Types of Telecommunications Media (1)

Twisted pair wire cable• Insulated pairs of wires historically used in

telephone service and to connect computer devices

Coaxial cable• Consists of an inner conductor wire

surrounded by insulation, called the dielectric

• The dielectric is surrounded by a conductive shield, which is surrounded by a non-conductive jacket. Coaxial cable has better data transmission rate than twisted pair


Twisted-pair ‘Discussion’

A type of cable that consists of two independently insulated wires

twisted around one another. One wire carries the signal while the

other wire is grounded and absorbs signal interference. Twisted-pair

cable is used by older telephone networks and is the least expensive

type of local-area network (LAN) cable. Other types of cables used

for LANs include coaxial cables and fiber optic cables.


Coaxial Cable ‘Discussion’

A type of wire that consists of a centre wire surrounded byinsulation and then a grounded shield of braided wire. The shieldminimizes electrical and radio frequency interference.

Coaxial cabling is the primary type of cabling used by the cabletelevision industry and is also widely used for computer networks.Although more expensive than standard telephone wire, it is muchless susceptible to interference and can carry much more data.Because the cable television industry has already connected millionsof homes with coaxial cable, many analysts believe that they arethe best positioned to capitalize on the much-heralded informationhighway.



Fiber-optic Cable• Many extremely thin

strands of glass or plastic bound together in a sheathing which transmits signals with light beams

• Can be used for voice, data, and video


Fiber Optic ‘Discussion’ (1)

A technology that uses glass (or plastic) threads (fibers) to transmitdata. A fiber optic cable consists of a bundle of glass threads, eachof which is capable of transmitting messages modulated onto lightwaves.

Fiber optics has several advantages over traditional metalcommunications lines:

Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry more data

Fiber optic cables are less susceptible than metal cables to interference Fiber optic cables are much thinner and lighter than metal wires Data can be transmitted digitally (the natural form for computer data) rather

than analogically.


Fiber Optic ‘Discussion’ (2)

The main disadvantage of fiber optics is that the cables areexpensive to install. In addition, they are more fragile than wire andare difficult to split.

Fiber optics is a particularly popular technology for local-areanetworks. In addition, telephone companies are steadily replacingtraditional telephone lines with fiber optic cables. In the future,almost all communications will employ fiber optics.



Microwave Communications• Line-of-sight devices which must be placed in

relatively high locations

• Microwave usage– Information is converted to a microwave signal, sent

through the air to a receiver, and recovered

Pretty picture



Satellite transmission• Communications satellites are relay stations that

receive signals from one earth station and rebroadcast them to another

• They use microwave signals

Pretty picture



Cellular transmission• Signals from cells are transmitted to a receiver and

integrated into the regular network

Pretty picture


Cellular ‘Discussion’Refers to communications systems, especially the Advance MobilePhone Service (AMPS), that divide a geographic region into sections,called cells. The purpose of this division is to make the most use outof a limited number of transmission frequencies. Each connection, orconversation, requires its own dedicated frequency, and the totalnumber of available frequencies is about 1,000. To support morethan 1,000 simultaneous conversations, cellular systems allocate aset number of frequencies for each cell. Two cells can use the samefrequency for different conversations so long as the cells are notadjacent to each other.

For digital communications, several competing cellular systems exist,including GSM and CDMA.



Infrared transmission• Involves sending signals through the air via light

waves

• Requires line-of-sight and short distances (a few hundred yards)

• Used to connect various computing devices such as handheld computers

Sorry, no pretty picture!


Terminology

Analog Signal A continuous, curving signal

Digital Signal A signal represented by bits

Modems Devices that translate data from digital to

analog and analog to digital


Analog ‘Discussion’ (1)

Almost everything in the world can be described or represented inone of two forms: analog or digital. The principal feature of analogrepresentations is that they are continuous. In contrast, digitalrepresentations consist of values measured at discrete intervals.

Digital watches are called digital because they go from one value tothe next without displaying all intermediate values. Consequently,they can display only a finite number of times of the day. Incontrast, watches with hands are analog, because the hands movecontinuously around the clock face. As the minute hand goes


Analog ‘Discussion’ (1)

around, it not only touches the numbers 1 through 12, but also the

infinite number of points in between.

Early attempts at building computers used analog techniques, but

accuracy and reliability were not good enough. Today, almost all

computers are digital.


Digital ‘Discussion’ (1)

Describes any system based on discontinuous data or events.Computers are digital machines because at their most basic levelthey can distinguish between just two values, 0 and 1, or off andon. There is no simple way to represent all the values in between,such as 0.25. All data that a computer processes must be encodeddigitally, as a series of zeroes and ones.

The opposite of digital is analog. A typical analog device is a clock inwhich the hands move continuously around the face. Such a clock iscapable of indicating every possible time of day. In contrast, a



digital clock is capable of representing only a finite number of times(every tenth of a second, for example).

In general, humans experience the world analogically. Vision, forexample, is an analog experience because we perceive infinitelysmooth gradations of shapes and colors. Most analog events,however, can be simulated digitally. Photographs in newspapers, forinstance, consist of an array of dots that are either black or white.From afar, the viewer does not see the dots (the digital form), butonly lines and shading, which appear to be continuous. Although



digital representations are approximations of analog events, they areuseful because they are relatively easy to store and manipulateelectronically. The trick is in converting from analog to digital, andback again.

This is the principle behind compact discs (CDs). The music itselfexists in an analog form, as waves in the air, but these sounds arethen translated into a digital form that is encoded onto the disk.When you play a compact disc, the CD player reads the digital data,translates it back into its original analog form, and sends it to the



amplifier and eventually the speakers.

Internally, computers are digital because they consist of discrete

units called bits that are either on or off. But by combining many

bits in complex ways, computers simulate analog events. In one

sense, this is what computer science is all about.


How a Modem Works

Modem Modulates a digital signal into an analog signal

for transmission via analog medium, then demodulates the signal into digital for receiving

Pretty picture


Modem ‘Discussion’ (1)

Acronym for modulator-demodulator. A modem is a device orprogram that enables a computer to transmit data over telephonelines. Computer information is stored digitally, whereas informationtransmitted over telephone lines is transmitted in the form of analogwaves. A modem converts between these two forms.

Fortunately, there is one standard interface for connecting externalmodems to computers called RS-232. Consequently, any externalmodem can be attached to any computer that has an RS-232 port,which almost all personal computers have. There are also modems


Modem ‘Discussion’ (2)

that come as an expansion board that you can insert into a vacant

expansion slot. These are sometimes called onboard or internal

modems.


Multiplexer

Multiplexer Allows several telecommunications signals to

be transmitted over a single communications medium at the same time

Pretty picture


Communicationslink

Multiplexor Front-endprocessor

Hostcomputer


Multiplexor ‘Discussion’

A communications device that multiplexes (combines) several signals

for transmission over a single medium. A demultiplexor completes

the process by separating multiplexed signals from a transmission

line. Frequently a multiplexor and demultiplexor are combined into a

single device capable of processing both outgoing and incoming

signals.

A multiplexor is sometimes called a mux.


Front-End Processor

Front-end processor… Special purpose computers that manage

communication to and from a computer system

Pretty picture


Incoming and outgoing jobs

Front-endprocessor

Mainsystem

Job 1

Job 2

Job 3

Job 4


Carriers and Services (1)

Carriers• Organizations that take the responsibility of ensuring telecommunications can

effectively take place between enterprises

Common carriers• Long-distance telephone companies

Value-added carriers• Companies that have developed private telecommunications systems and offer

their services for a fee

Switched lines• Lines that use switching equipment to allow one transmission device to be

connected to other transmission devices (e.g., standard telephone line)

Dedicated line• A line that provides constant connection between two points. No switching or

dialing is needed



Private branch exchange (PBX) Communication system that can manage both voice and data transfer

within a location (e.g. a building) and to outside lines

Wide area telecommunication service (WATS) Billing method for heavy users of voice services

Phone and dialing services Includes automatic number identification (a.k.a. caller ID) Integration of telephones and personal computers Access code screening Call priorities One number portability (use anywhere) Intelligent dialing (auto re-dial for a busy number)


ISDN• ISDN = Integrated Services Digital Network

• Technology that uses existing common-carrier lines to simultaneously transmit voice, video, and image data in digital form

Pretty picture



T1 carriers• An expensive service developed by AT&T to

increase the number of voice calls that could be handled through existing cables

Digital subscriber lines (DSL)• Uses existing phone wires going into today’s homes

and businesses to provide transmission speeds exceeding 500 Kbps at a cost of $100 - $300 per month



Networks and Distributed Processing

Centralized processing Data processing that occurs in a single location or

facility Decentralized processing

Data processing that occurs when devices are placed at various remote locations

Distributed processing Data processing that occurs when computers are

placed at remote locations but are connected to each other via telecommunications devices


Network Concepts and Considerations

Network Topology A logical model that describes how networks

are structured or configured Topologies…

• Ring (see chapter 1)• Bus (see chapter 1)• Star (see chapter 1)• Hierarchical• Hybrid


Hierarchical• Uses treelike structures

with messages passed along the branches of the hierarchy

Hybrid• Network made up of

various types of topologies


Network Types

Local area network (LAN) Connects computer systems and devices in the same

geographic area (can be Ring, Bus, Hierarchical, Star, Hybrid)

Wide area network (WAN) Ties together large geographic regions using

microwave and satellite transmission or telephone lines

International network Links systems between countries


Terminal-to-Host Connection

Applications and databases reside on the same host computer

User interacts with the application using a “dumb terminal”

Hostcomputer

Target PC

“dumb terminal”


File Server Connection

Applications and databases reside on the same host computer

File server transfers data and programs to PCs on the network, where these target PCs perform most of the processing

Hostcomputer

File downloaded to user

File server

Target PC


Client/Server Connection

Applications and databases reside on specialized host computers

Servers do most or all of the processing and transmit the results to the client

Client Server

Server ServerClient


Advantages & Disadvantages of Client/Server

Advantages Reduced cost potential Improved Performance Increased Security

Disadvantages Increased cost potential Loss of control Complex multi-vendor

environment


Communications Software and Protocols (1)

Communications software• Provides error checking, message formatting, communications

logs, data security and privacy, and translation capabilities for networks

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



Protocol• Rules that ensure communications among

computers of different types and from different manufacturers.



Open Systems Interconnection (OSI) Model Serves as a standard model for network architectures

and is endorsed by the International Standards Committee

Communication functions are represented in seven layers to promote the development of modular networks. Designed to permit communication among different computers from different operating systems

Seven layers (see figure 6.20)



TCP/IP• TCP/IP = Transmission Control Protocol/Internet Protocol

Standard originally developed by the U.S. government to link defense research agencies; it is the primary communication protocol of the Internet

Systems Network Architecture (SNA)• IBM communication protocol

Ethernet• Protocol standard developed forLANs using a bus topology

X.400 and X.500• An international standard for message handling and network

directories


Bridges, Routers,Gateways and Switches

Bridge• Connects two or more networks, with the same protocol, at the

media control portions of the data link layer

Router• Operates at the network level of the OSI model and features

more sophisticated addressing software than bridges. Can determine preferred paths

Gateway• Operates at or above the OSI transport layer and links LANs or

networks that employ different architectures and use dissimilar protocols

Switch• Routes or switches data to its destination

Schematic


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Application

Presentation

Session

Transport

Network

Data link

Physical

Machine#1

Machine#2

Machine#3

Gatewaybox

Machine#4

Bridgebox

Routerbox

Media


Telecommunications Applications (1)

Linking personal computers to mainframe computers Download and upload information

Voice mail Enables users to leave, receive, and store verbal

messages for and from other users Electronic mail (e-mail)

Enables a sender to connect a computer to a network, type messages, and send it to another person on the network



Electronic software distribution• Involves installing software on a file server for users to share by

signing onto the network and requesting that the software be downloaded onto their computers over a network

Electronic document distribution• Transporting documents -- such as sales reports, policy manuals,

and advertising brochures -- over communications lines and networks

Telecommuting• Enables employees to work away from the office using personal

computers and networks to communicate via electronic mail with other workers and to pick up and deliver results



Videoconferencing Allows participants to conduct long-distance

meetings “face to face” while eliminating

Pretty picture



Electronic Data Interchange (EDI)• Uses network systems and follows standards and

procedures that allow output from one system to be processed directly as input to other systems, without human intervention

Pretty picture


EDI link

EDI link EDI link

Vendor Customer

Vendor Customer

Third-partyclearing house

(a)

(b)



Public network services Services that give personal computer users access to

vast databases and other services, usually for an initial fee plus usage fees

Specialized and regional information services Specialized electronic bulletin boards and e-mail

services targeting particular interests.

Distance learning Use of telecommunications to extend the classroom


End of Chapter 6

Chapter 7

1010-Chapter6

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