Chapter 01 - Comp Nwks & Datacom

8/7/2019 Chapter 01 - Comp Nwks & Datacom

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CSC 3200: Computer Networks

and Data Communication

By Muwonge S. Bernard, Msc. DCSE

Makerere University

Faculty of Computing & IT

[email protected]


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Learning Objectives

Define a Computer Network;

Discuss the advantages of using a network.

Describe the different types of Networks.

Identify differences between a LAN & WAN

Identify a peer-to-peer network.

Identify a server-based network.

Identify server functions and assign specializedservers as needed.

Determine which type of network is appropriate

for a site.


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Course Outline

y Introduction to Computer Networks and Devices,

Structure of communication network (Topologies),

y Transmission media: magnetic media, twisted pair, coaxial,fiber-optics;

y The OSI/ISO reference model;

y Data encoding: straight, Manchester, differential Manchester,

y Satellite;

y Digital versus Analog transmission;

yModems,

y Modulation and their standards, codes and pulse codemodulation;

y Integrated Services Digital Networks (ISDN);

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Course Outline (Cont.)

Network Access Protocols;

LAN standards:802.3 (Ethernet), 802.4 (token bus), 802.5

(token ring);Computer Network security, Active and Passive Attacks;

Network layer and Network layer protocols;

Transport layer and Transport layer protocols.

Furthermore, the course considers problems on each layer ofa multilayered communication model, and describes sometypical solutions to such problems.

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Course Assessment

In order to pass the course unit, a student must obtain aminimum mark of 50%. All assignments MUST be handed inon time.

1. Coursework Test = 20%

2 Assignments = 20%

TOTAL COURSE WORK= 40%

2. Examination (End ofSemester)

Final Examination = 60%OVERALLTOTAL = 100%

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What Is a Network?

A system in which a number of independent

computers are linked together to share data

and peripherals, such as hard disks and

printers

The ability to share information efficiently is what

gives computer networking its power and its

appeal A team located in different places around the

world that communicates through

teleconferencing, e-mail, and multimedia

presentations over the Internet


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Introducing Computer Networking

A computer network consists of two or more

computers connected to each other by a

transmission medium that allows them to share data.

The five components that make up a data

communications system are

the message,

sender,

receiver,

medium, and

protocol


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Components of a Data communication

Message. The message is the information (data)

to be communicated. Popular forms of

information include text, numbers, pictures,

audio, and video.

Sender. The sender is the device that sends the

data message. It can be a computer, workstation,

telephone handset, video camera, and so on.Receiver. The receiver is the device that receives

the message. It can be a computer, workstation,

telephone handset, television, and so on.


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Transmission medium.

The physical path by which a message travels fromsender to receiver.

Some examples of transmission media include

twisted-pair wire, coaxial cable, fiber-optic cable, and

radio waves.

Protocol.

A set of rules that govern data communications. It

represents an agreement between the communicatingdevices.

Without a protocol, two devices may be connected

but not communicating, just as two people speaking

different languages may not understand each other.


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Data flow


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Simplex In simplex mode, the communication is

unidirectional, as on a one-way street. Only one of

the two devices on a link can transmit; the other

can only receive (see Figure 1.2a). Keyboards and traditional monitors are examples

of simplex devices. The keyboard can only

introduce input; the monitor can only accept

output.

The simplex mode can use the entire capacity of

the channel to send data in one direction.


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Half-Duplex

In half-duplex mode, each station can both transmitand receive, but not at the same time. :

When one device is sending, the other can only

receive, and vice versa (see Figure 1.2b).

Full-Duplex

In full-duplex mode, both stations can transmit and

receive simultaneously (see Figure 1.2c)

One common example of full-duplex communication

is the telephone network.

When two people are communicating by a telephone

line, both can talk and listen at the same time.


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Networked Computers- fig.1

Computers may be

connected to others to

share data & send

documents.This connecting together

of computers and other

devices is called a

network, andThe concept of

connected computers

sharing resources is

called networking.


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Why Use a Computer Network?

Networks increase efficiency and reduce

costs. Computer networks achieve these goals

in three primary ways:Sharing information (or data)

Sharing hardware and software

Centralizing administration and support


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Sharing Information (or Data)

The ability to share information quickly and

inexpensively is one of the most popular uses

of networking technology esp. by e-mail. Many businesses have invested in networks

specifically to take advantage of network-based e-

mail and scheduling programs.

By making information available for sharing,networks can reduce the need for paper

communication, increase efficiency, and make

data available simultaneously to users who need it.


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Sharing Information contd

Managers can use these utilities to

communicate quickly and effectively with

large numbers of people,and to organize and schedule meetings with

people drawn from an entire company or

business enterprise far more easily than was

previously possible.


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Sharing Hardware and Software

Networks make it possible for several people

to share data and peripherals simultaneously.

If many people need to use a printer, they canall use the printer available on the network.

For instance, 5 workstations may share a

printer in a networked environment as shownin Figure below


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Sharing a printer in a networking

environment fig.3


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Sharing Hardware and Software

Networks can be used to share and standardize

applications, e.g. word processors, spread

sheets, inventory databases, etc, to ensure that

everyone on the network is using the sameapplications & the same versions of those

applications.

This allows documents to be shared easily &creates training efficiencies: it is easier for

people to master one word processing

application than to try to learn 4 or 5 different

word rocessin a lications.


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Centralizing Administration and

Support

Networking computers can simplify support

tasks as well.

It is far more efficient for technical personnelto support one version of one operating system

or application and to set up all computers in

the same manner than to support many

individual and unique systems and setups.


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Types of Computer Networks

Computer Networks are classified

according to the distance between

individual computers that are

attached to the network. The

classification includes thefollowing:

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Personal Area Network (PAN)

A computer network used forcommunication among computer

devices close to one person.Some examples of devices thatmay be used in a PAN areprinters, fax machines, telephonesor scanners.

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Types of Networks:

LocalArea Network LAN:

Is the basic building block of any computernetwork.

Can range from simple (two computers connectedby a cable) to complex (hundreds of connectedcomputers and peripherals throughout a majorcorporation).

The distinguishing feature of a LAN is that it isconfined to a limited geographic area.

A LAN covers a room, a building or a campus.


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ATypical set up of a LAN fig.4


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Campus Area Networks

A network that connects two or

more LANs but that is limited to

a specific geographical area such

as a college campus, industrial

complex, or a military base etc

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Metropolitan Area Network (MAN)

A network that connects two or more

Local Area Networks or Campus Area

Networks together but does not extendbeyond the boundaries of the immediate

town, city, or metropolitan area.

Multiple routers, switches & hubs areconnected to create a MAN.

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Wide Area Network - WAN

Has no geographical limit (see Figure below).

It can connect computers and other devices

on opposite sides of the world.A WAN is made up of a number of

interconnected LANs.

The ultimate WAN is the Internet.

continued


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ATypical set up of a WAN fig.5

continued


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Summary

The primary reasons for networking

computers are to share information, to share

hardware and software, and to centralizeadministration and support.

A local area network (LAN) is the smallest

form of a network and is the building block

for larger networks.

A wide area network (WAN) is a collection of

LANs and has no geographical limitation.

continued


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Network Configuration

Network ConfigurationOverview

In general, all networks have certain

components, functions, and features in

common see Figure 6. These include:

ServersComputers that provide shared

resources to network users.

ClientsComputers that access shared

network resources provided by a server.

MediaThe wires that make the physical

connections.


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Network Configuration Overview

Shared dataFiles provided to clients by

servers across the network.

Shared printers and other peripheralsAdditional resources provided by servers.

ResourcesAny service or device, such as

files, printers, or other items, made available

for use by members of the network.


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Network Configuration fig 6


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Summary

Networks are classified into two principal

groups based on how they share information:

Peer-to-peer networks and server-based networks.

In a P2P network, all computers are equal. :

They can either share their resources or use

resources on other computers.


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In a server-based network, one or more

computers act as servers and provide the

resources to the network. The other computers are the clients and use the

resources provided by the server.


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Comparison of Network Types

P2P Network

Good for 10 or fewer

computers

Security established by theuser of each computer

Individual users responsible

for their own administration;

no full-time administratornecessary

Server-based Network

Limited only by server and

network hardware

Extensive and consistentresource and user security

Centrally located for

network control; requires at

least one knowledgeableadministrator


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Types ofTopology/Configuration

In networking, the term "topology"refers to the layout of connected

devices on a network.Networktopology is the study ofthe arrangementormappingof theelements (links, nodes, etc.) of anetwork, especially the physical(real) and logical (virtual)interconnections between nodes.

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There are two basic categories of

network topologies:

Physical topologies: Computers

linked together with network cablesand hardware devices.

Logical / Virtual topologies:

Concerned with the way information

is transmitted from node to node.

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Bus Topology

y

Linear busyAll of the nodes of the network are

connected to a common transmission

medium which has exactly two endpointsthat are terminated .

yUsually the information is transmitted back

and forth along the cable, while each nodelooks out for the destination address.



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Distributed busThe type of network topology in

which all of the nodes of the

network are connected to a

common transmission medium

which has more than twoendpoints.



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Advantages ofaLinear BusTopology

yEasy to connect acomputer/peripheral to a linear bus.

yRequires less cable length than a startopology.

Disadvantages ofaLinear Bus

TopologyyEntire network shuts down if there is

a break in the main cable.2/14/2011 Bernard S. Muwonge 42


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yTerminators are required at both

ends of the backbone cable.yDifficult to identify the problem if

the entire network shuts down.yNot meant to be used as a stand-

alone solution in a large building.



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StarTopology

yEach of the nodes of the network

is connected to a central node

with a point-to-point link in a

'hub'and 'spoke'fashion. A

switch is most commonly usedthese days instead of a hub.

Why?????2/14/2011 Bernard S. Muwonge 44


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Advantages of a StarTopology

Easy to install and wire.

No disruptions to the network when

connecting or removing devices.Easy to detect faults and to remove parts.

Data transfer between the central server

and the nodes is relatively low, therefore alow cost cable like twisted pair cable canbe used to connect the nodes to the server.

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Disadvantages of a StarTopology

Requires more cable length than a

linear topology.

If the switch or concentrator fails,nodes attached are disabled.

More expensive than linear bustopologies because of the cost of

the concentrators or switches.47


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Ring Topology

Each of the nodes of the network

is connected to two other nodes in

the network and with the first andlast nodes being connected to

each other, forming a ring.Data flows from one node to

another.2/14/2011 Bernard S. Muwonge 48


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Advantages

All nodes on the network have an equal

chance of transmitting data.

Disadvantages

Failure of one node leads to a shut down of

all the others.

Difficult to add or delete nodes because of

the physical lay out.

The token may get lost.


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Advantages

All nodes on the network have an

equal chance of transmitting data.

Disadvantages Failure of one node leads to a shut

down of all the others.

Difficult to add or delete nodes

because of the physical lay out.

The token may get lost.


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Mesh/Fully connected Topology

A network topology thatresembles a wire mesh. A mesh

network in which every device

connects to every other is called a

full mesh.

Mostly applicable to WANs forexample the internet.



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Tree Topology

Tree topologies integrate multiple

star topologies together onto a bus.Many servers can exist on thisnetwork due to the tree like

structure.Particularly helpful for schools anduniversities, as each department can

have their individual networks, butstill connect to the big network insome way.



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Advantages ofaTree Topology

Supported by several hardware andsoftware venders.

This bus/star hybrid approach supports

future expandability of the network muchbetter than a bus (limited in the number

of devices due to the broadcast traffic it

generates) or a star (limited by thenumber of hub connection points) alone.



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Disadvantages of a Tree Topology

Overall length of each segment is

limited by the type of cabling

used.If the backbone line breaks, the

entire segment goes down.More difficult to configure and

wire than other topologies57


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Hybrid network topologies

The hybrid topology is a type of

network topology that is

composed of one or more

interconnections of two or more

networks that are based upondifferent physical topologies.



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Considerations When Choosing a

Topology

Money. A linear bus network

may be the least expensive way to

install a network; you do not haveto purchase concentrators.

Length of cable needed. Thelinear bus network uses shorter

lengths of cable.2/14/2011 Bernard S. Muwonge 60


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Future growth. With a star topology,

expanding a network is easily done by

adding another concentrator.

Cable type. The most common cable in

schools is unshielded twisted pair, which

is most often used with star topologies.

Distances

Existing Network Infrastructure


The Logical / Signal Topology


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The Logical / Signal Topology

The Ring Logical Topology. Based on

the principle of communicating in turn i.e

only one node communicates at a time.

Consists of;

TokenRing:A token (data packet)

circulating in a loop determines which

computer transmits information one at a

time, hence no collision is likely to occur.



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Fiber DistributedData Interface (FDDI)

Another type of token ring technology

in form of a dual ring, the outer being the primary ring

and the inner the secondary.

Data usually travels on the primary ring, on failure, the

secondary ring is used. Thus more reliable than theprevious.

Often used with MANs or with very large LANs such as

those connecting several buildings in a complex or site.

This technology uses a fiber-optic cable as a result; it

gives a high-speed performance with the additional

advantages of token passing ring topology.


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The Bus Logical Topology

If a node on the network has data for another

node, the sending node broadcasts the data to

the entire network.

If the data belongs to one of the nodes, they

keep it, else they ignore it. Ethernet is the bestknown example.

Collision of data is likely to occur, so to

overcome these collision problems, Ethernethardware is equipped with collision detection

sensors. The data which collides is ignored,

and the sender resends the data.2/14/2011 Bernard S. Muwonge 64


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Questions

List three factors that can influence the choice

of whether to implement a peer-to-peer or

server-based network configuration.

What are the advantages of a peer-to-peer

network?

What are the advantages of a server-based

network?


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Q & A

In life, always expect questions, but do not expectanswers

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