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Computers AreYour Future

2005 Prentice-Hall, Inc.

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Computers Are Your Future Chapter 6

2005 Prentice-Hall, Inc Slide 2

Computers Are Your Future

Chapter 6

Networks: Communicating andSharing Resources

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What You Will Learn About

Basic networking concepts

The three major types of physical media

Bandwidth

How modems transform digital computer signals into

analog signals

Circuit switching and packet switching networks

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What You Will Learn About

The importance of protocols in a computer network

The advantages of a network

Peer-to-peer and client/server LANs

The most widely used LAN protocol

Ways that businesses use WANs

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Network Fundamentals

A computer networkconsists of

two or more computers linked

together to exchange data and

share resources.

Communicationsis the process

of sending and receiving

messages.

Communications channelsare

the paths through which messages

are passed.

Communications devices

transform electronic signals.

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Physical InfrastructurePhysical infrastructure refers to cables, modems, switches,

and routers. Twisted-pairTwo insulated wires twisted around each other;

the same type of wire as that used for telephones Types of twisted-pair technologies:

Leased line (T1)

Integrated Services Digital Network (ISDN) Digital Subscriber Line (DSL)

Coaxial cableConsists of an insulated center wiresurrounded by a layer of braided wire; the same type of wire asthat used for cable TV

Fiber-optic cableType of fiber glass cable that transmitsdata in the form of light impulses; can carry more data forlonger distances than other wire

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Bandwidth

Bandwidthis the amount of data that can betransmitted through a communications channel.

Digital bandwidth is measured in bits per second

(bps), kilobits per second (Kbps), megabits per

second (Mbps), or gigabits per second (Gbps).

Low bandwidth is 56 Kbps and high bandwidth is

622 Mbps.

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Modulation

DigitalAnalog

Analog Digital

Demodulation

Modems: From Digital to Analog and Back

Modemsare devices that transform signals when sending

and receiving transmissions.

ModulationTransforming digital signals to analog

DemodulationTransforming analog signals to digital

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Internal Modem External Modem

Modems: From Digital to Analog and Back

Two types of modems:

Internal modemsFit into a computers expansion slot

External modemsConnect to a port outside the system

box

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Asynchronous and Synchronous

Communications

Asynchronous communicationis a method of

networking in which bits of data are sent and

received one bit at a time; each byte contains a startand stop bit.

Synchronous communicationrequires a

synchronization signal that identifies units of data.

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Modulation Protocols

Modulation protocolsare communications standardsthat modems conform to.

Data transfer rateis the rate at which two modems

can exchange data. It is measured in bits per second

(bps).

A modulation protocol called V.90enables modems

to transfer data at 56 Kbps.

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Cable Modems

Cable modemsenable computers to access theInternet by way of a cable TV connection.

Data is transferred through a coaxial cable.

Bandwidths range from 500 Kbps to 1 Mbps. Bandwidth is divided among the number of

subscribers using it.

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Circuit switchingNetworks create an end-

to-end circuit between the

sending and receivingcomputers.

Electronic switches

establish and maintain the

connection.

Switching and Routing Techniques

Packet switchingOutgoing messages are

divided into fixed-size

data units called packets.

Packets are numbered andaddressed to the receiving

computer.

Routers examine the

packets and send them to

their destination.

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Advantages Disadvantages

Circuit switching

Voice and real-time

transmission

No delivery delays

Costly

A direct electrical

connection between thecomputers is required

Packet switching

Efficient, less

expensive, and reliable

Will function if part of

the network is down

Delays in receiving

packets

Not ideal for real-time

voice communication

Advantages and Disadvantages of Circuit and

Packet Switching

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Protocols

Protocolsare fixed, formalized standards that specify

how computers can communicate over a network.

Protocol suiteThe total package of protocols that

specify how a network functions

C A C 6

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Network Layers

Network architecture is the overall design of a network.

The network design is divided into layers, each of which

has a function separate from that of the other layers. Protocol stackThe vertical (top to bottom) arrangement

of the layers; each layer is governed by its own set of

protocols

user

physical media

user

physical media

receiving

sending

protocol

layerstack

C A Y F Ch 6

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Reduced hardware costs

Users share equipment

Connected people

People can worktogether without being

at the same location

Groupware enables

sharing of schedulesand communications

Advantages of Networking

Shared applications

Users share software

File server enables all

users to work with the

same application program

Building information

resources

Users create common

pools of data that can beaccessed by employees

C t A Y F t Ch t 6

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Local Area Network (LAN)

Links computers within a

building or group of

buildings

Uses direct cables, radio, or

infrared signals

Types of Computer Networks

Wide Area Network (WAN)

Links computers separated

by a few miles or thousands

of miles

Uses long-distance

transmission media

C t A Y F t Ch t 6

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Local Area Networks (LANs)

Network access is controlled by a network administrator.

Users can access software, data, and peripherals.

LANs require special hardware and software.

Computers connected to a LAN are called workstations

or nodes.

Types of LANs:

Peer-to-peer

Client-server

C t A Y F t Ch t 6

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LAN Hardware and Software

Networking HardwareNetwork interface card

(NIC) Provides the

connection between the

computer and the networkInserted into a computers

expansion slot

Networking SoftwareOperating system that

supports networking

(Unix, Linux, Windows,

Mac OS)Additional system

software

NIC

C t A Y F t Ch t 6

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Peer-to-Peer Networks

All computers on the network are treated as equal.There are no file servers.

Users decide which files and peripherals to share.

Peer-to peer is not suited for networks with many

computers.

Peer-to-peer is easy to set up. Example: home

networks


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Client-Server Networks

Typical corporate networks are client-server.

Client-server requires various topologies or physical layouts.

The network requires file servers, networked computers(clients), and a network operating system (NOS).

Clients send requests to servers for programs and data, and

to access peripherals.


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LAN Topologies

The physical layout of a LAN is called its topology.

Topologies resolve the problem of contention, whichoccurs when multiple users try to access the LAN at thesame time.Collisions or corrupt data occur when different computers use

the network at the same time.

Bus topology Called a daisy chain Every workstation is connected to a

single cable

Resolves collisions throughcontention management

Difficult to add workstations

Star topology Contains a hub or central wiring

concentrator

Easy to add workstations

Resolves collisions through

contention management

Ring topology All workstations are attached in a

circular arrangement

A special unit of data called atokentravels around the ring

Workstations can only transmit datawhen they possess a token


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Wide Area Networks (WANs)

WANsare similar to long-distance telephone systems.

They have a local access number called a point of presence(POP).

They contain long-distance trunk lines called backbones.


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WAN Applications

LAN-to-LAN

WANs are used to connect

LANs at two or more

geographic locations.

Companies use WANs to

connect their branches to

one network system.

Transaction Acquisition

Information about

transactions is instantly

relayed to the corporate

headquarters.

Point-of-sale(POS)

terminals relay

transactions to central

computers through WANs.


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Backbones

Backbones, high-capacity transmission lines, are

regional, continental, or transcontinental. Internet backbones can carry 2.5 gigabits of data per

second.


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WAN Protocols

X.25is the oldest packet switching protocol. It is used

by automated teller machines and credit card

authorization devices.

New protocols designed for digital lines and fasterdata transfer rates are: Switched Multimegabit Data Service(SMDS)

Asynchronous Transfer Mode(ATM)


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Public Data Network (PDN)

PDNis a for-profit data communications network.

Fees are paid on a per-byte-transferred basis.

They offer good security and network availability.


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Virtual Private Network (VPN)

A virtual private networkconsists of lines that are

leased to a single company.

The network is not open to the public.

It is the most secure type of WAN.


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Chapter 6 Summary

Computer networks link two or more computers to exchange

data and share resources. Two types of computer networks:

Local area network (LAN)

Wide area network (WAN)

Computer networks:

Reduce hardware costs

Enable users to share applications

Provide a means to pool an organizations data

Foster teamwork

Computer networks require physical media such as telephonewire, coaxial cable,or fiber-optic cable to connect thecomputers.


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Chapter 6 Summary continued

Modems transform analog and digital signals. Network protocols enable the network to function smoothly.

Data is sent through the network by switching and routing

techniques.

LAN topologies include:Bus topology

Star topology

Ring topology

Wide area networks are used to link computers throughout theworld.

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