Chp 1 Intro and Basic Concepts

8/7/2019 Chp 1 Intro and Basic Concepts

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CNB2124 DATA COMMUNICATION

&COMPUTER

NETWORKING


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Course Assessment Participation + Forum ..10% Assignments(2) ..30% Quizzes (2)..10%

Final Exam . 50% Total:... 100%


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CHAPTER 1CHAPTER 1

Introduction andIntroduction and

Basic ConceptsBasic Concepts

Data CommunicationNetworksProtocols and Standards

Standard Organizations


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Data Communication

What is Data Communications?What is Data Communications? is the exchange of data between two devices via some form

of transmission medium such as wire cable. An effective data communications has 3 characteristics:

Delivery Correct destination Receive by the intended device or user

Accuracy Deliver data accurately Altered data unusable

Timeliness Deliver data in a timely manner Real time transmission deliver data as they are

produced, in the same order that they are produced,without delay.


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Medium - physical path by

which a message travel.

E.g.: twisted pair, coaxial

cable, fiber optic cable, or

radio waves (terrestrial or

satellite microwave)

Receiver - device that

receives the message. E.g.:

Computer,

Workstation,

Telephone handset,

TV, and so on.

Components of a Data Comm.Components of a Data Comm.

SystemSystem

Message information(data)To be communicated. E.g.:

Text, numbers, sound, or video,

Or any combination of these.

Protocol- set of rules

that governs data

Communication. Withoutprotocol it may connected

but not communicate.

Sender - device that sends

the message. E.g.:

Computer,

Workstation,

Telephone handset,

TV, and so on.


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NETWORKS

IS a set of devices (nodes) connected by

communication links. Node (computer,

printer, or any other device capable ofsending and/or receiving data generated

by other nodes on the network)

Categorized by geographic scope: LANs,MANs, WANs


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NETWORKS

Distributed processing security/encapsulation

Limit interaction with the entire system. e.g.: ATM user access own account without accessing to thebanks entire database.

security through redundancy Running the same program at the same time forsecurity purposes. Space shuttle system.

distributed databases Information stored and manipulated anywhere on the

internet. collaborative processing

Multiple computers and users interact on a task. faster problem-solving


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Measured by

transit time (amount oftime required for a

message to travel from

one device to another )

response time (elapsed

time between inquiryand a response)

No. of users, type of

transmission medium,

hardwares capabilities,

softwares efficiency.

Measured by frequency of

failure, time taken torecover, networks

robustness in catastrophe.

Protect data from

unauthorized access


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A protocol is a set of rules that govern data communications.

Protocol defines:

Whatis communicated

Howit is communicated

When it is communicated

The key elements of a protocol are:

syntax: structure/format of the data (the orderin which they are presented).

semantics :meaningof each section of bits (does an address identify the routeto be taken or the final destination of the message?)

timing: when data should be sent and how fast they can be sent. Examplesender produces data at 100 Mbps but the receiver can process data at only 1

Mbps thus the transmission will overload the receiver and data largely lost.

PROTOCOL AND STANDARDS

PROTOCOL


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legislated by an officially recognized

body-- e.g. by committee

RS232

NOT been approved by an organized

body but have been adopted as standardsthrough widespread use.

example. Hayes modem command set,

IBM PC bus

provides a model for development that makes it possible for a

product to work regardless of the individual manufacturer.Two categories of standards:

STANDARD


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Standards are supported by manufacturers and users to promote

interoperability of equipment.

Open interface descriptions for ease of maintenance and support.

Greater competition of products among manufacturers and resulting

lower costs for users.

Standard tooling lowers manufacturing cost and increases their profit

margin.

Standard interfaces allow fair comparison of performance among

competing products.

WHY DO WE HAVE STANDARDS?


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Five general concepts provide the basis toFive general concepts provide the basis to

understand the relationship betweenunderstand the relationship between

communicating devices:communicating devices: Line configuration

Topology

Transmission mode Categories of networks

Internetworks


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Methods are needed where channel-sharingcan be enabled so that

stations can share a single physical channel and still maintain

performance.

Line configuration defines the attachment of communication devices

to a link.

TWO CATEGORIES OF LINE CONFIGURATION:

Point-to-point line configuration

Multipoint line configuration

LINE CONFIGURATION


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Point-to-point lineconfiguration

It is a line dedicated between two devices


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Multipoint line configuration Also called as multidrop.

More than two specific devices share [spatiallyor temporally] a single link.

Spatially shared: Several devices can use the

link simultaneously

Timeshare: Users must take turns.


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Defines the physical or logical arrangement ofDefines the physical or logical arrangement oflinks in a networklinks in a network

Physical meaning the actual physical layout of stations.Logical meaning an LAN architecture which defines

how signals actually travel over the network.

NETWORK TOPOLOGIES

Topology

Mesh Star Bus RingTree Hybrid


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Mesh topology

Every device has a dedicated point topoint link to every other device.

The link carries traffic only between those2 devices.

A fully connected mesh network has n(n-

1)/2 physical channels to n devices. Every device must have n-1 I/O ports.

Best used in Backbone Networks.


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Mesh Topology Advantages:

Less traffic on each link. Very robust..if a link becomes unusable, there

are other links available to transport traffic.

Very private and secure because of thededicated line.

Easy to troubleshootyou know exactly which

link is broken allowing you to bypass that link

until it is operational again.


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Mesh Topology

Disadvantages The amount of cabling.

The number of I/O ports

Installation and configuration is difficult. Dedicated lines are expensive.

Hardware to connect linksthe I/O ports

and cable are expensive. Heavy wiring requires extra support in

ceilings, walls, and support.


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Star topology

Star Topologies havededicated point to

point links only to a

central controller

usually called a hub. Doesnt allow direct

traffic between

devices because the

hub/controller takescare of sending traffic.


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Star Topology Advantages

Less expensive than a mesh.

Only one I/O port required.

Easy to install. Easy to troubleshoot broken links so it is

ROBUST.

Less cabling. Devices can be moved around quite easily.


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Star Topology

Disadvantages More cabling than with a linear bus.

If the hub/controller dies.so does the

network.


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Tree Topology Variation of the Star.

Nodes in the Tree are linked to a hub but

not every device plugs into the central hub.

Most devices connect to a secondary hub

that in turn is connected to a central hub. Central hub in an active hub containing a

repeater to regenerate bit patterns.

Secondary hubs can be active or passive.


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Tree topology


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Tree Topology Advantages

Less expensive than a mesh.

Only one I/O port required.

Easy to install. Easy to troubleshoot broken links so it is ROBUST.

Less cabling.

Devices can be moved around quite easily.


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Bus topology Multipoint: One cable acts as a

backbone to link all the devices in a

network. Drop line: a connection running

between the device and main cable. Tap: a connector that either splices

into the main cable or punctures thesheathing of the cable to create a

contact with the metallic core. Signal degrades due to energy

being transformed into heat. So,there is limitation on the number oftaps allowed.

Adv: easy to install, less cabling.

Disadv: Limit on number of taps andthe distance between taps, difficultto identify fault, signal degradation,modification is difficult.


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Ring topology Employs a dedicated

point to point lineconfiguration betweeneach device and thedevice on its left and thedevice on its right.

A signal passes in onedirection over the entirering until it reaches adestination.

Each device has arepeater to regeneratethe signal.


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Ring Topology Advantages &Disadvantages Easy to Install and Reconfigure

Device fault isolation is simplified because

signals circle all the time. When a device

doesnt receive a signal, you can pinpointwhich device isnt working.

Link faults are more difficult to troubleshoot.

One break brings down the whole network.

H b id t l


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Hybrid topology

Network combines several topologies as subnetworks linkedtogether in a larger topology. Example one department may decided to use a bus topology

while another department has a ring. The two can be connected to each other via a central

controller in a star topology.


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Transmission Modes

Simplex: unidirectionalone-way street.

Half-Duplex: Each can transmit and receive but not at

the same time.walkie-talkies.

Full-Duplex: Both stations can transmit and receive and

the same timeyou and the telemarketer as you try to

interrupt him/her in the middle of their little speech tryingto sell you something. Another examplea 2 lane

highway with traffic in both directions.


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CATEGORIES OF NETWORK


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Privately owned.

Connection within one building, limited to few kilometers.

Designed to allow resource sharingTransmission media: normally only one type.

Topology: bus, ring and star are the most common.


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Designed to extent over entire city.

Maybe wholly owned or provided by a public company.

MAN


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long distance transmission, over large geographical area.

May utilize public, leased, or private communication

devicesMay be wholly owned or publicly owned

WAN


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When 2 or more networks are connected, they become aninternetwork, or internet.

Individual networks are joined into internetworks by the use of

internetworking devices

Do not confuse internet and Internet.

internet = an interconnection of networks

Internet = specific worldwide network

INTERNETWORKS

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Chp 1 Intro and Basic Concepts