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Chapter 1

Introduction

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Chapter 1

At the end of the discussion, students will be

able to identify the fundamental characteristics

of a data communication system.

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Data communications and networking is changing we do business and the

way we live.

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1.1 Data Communication

Components

Data Representation

Direction of Data Flow

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TELECOMMUNICATION

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Figure 1.1 Simple Network Diagram

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Delivery System must deliver the data to the

correct destination Accuracy

System must deliver the data accurately Timeliness

System must deliver the data in timely manner

Jitter Variation in the packet arrival time.

Data communication fundamental characteristics

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Message Information (data) to be communicated.

Sender Device that sends the data message.

Transmission Medium Carries data.

Receiver Device that receives the message.

Protocol Set of rules that govern data

communication.

Five components of data communication

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Figure 1.1 Five components of communication system

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Information today comes in different forms.

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Text Represented as a bit pattern

Numbers Also represented as a bit pattern

Images Composed of a matrix of pixels

Audio Recording or broadcasting of sound or

music Video

Recording or broadcasting of picture or movie

Data Representation

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Communication between two devices can be either simplex, half-duplex and

duplex.

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Simplex

In simplex mode, the communication is unidirectional.

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Half-duplex

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

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Full-duplex

In full-duplex mode both stations can transmit and receive simultaneously

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1.2 Networks

Distributed ProcessingNetwork CriteriaPhysical StructuresCategories of Networks

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A network is a set of devices (called as nodes) connected by communication

links.

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Distributed processing is the division of tasks in a network among its

computers.

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A network must meet a certain number of criteria: performance, reliability

and security.

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Performance Depends on a number of factors,

including transit time, response time, number of users, type of transmission medium, throughput and delay.

Reliability Measured by the frequency of failure, the

time it takes a link to recover and the network’s robustness in catastrophe.

Security Includes protecting data from

unauthorized access, protecting data from damage and development, etc.

Network Criteria

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A network is two or more devices connected through links.

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Point-to Point (P2P) Provides a dedicated link between two

devices.

Types of Connection

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Multipoint (P2MP) More than two specific devices share a

single link. Also called multidrop/broadcast connection.

Types of Connection

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Physical topology refers to the way in which a network is laid out physically.

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Mesh topology Every device has a dedicated point-to-

point link to every other device.

Basic Topologies

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ExampleExample

Consider a mesh network with 6 nodes, calculate how many cable connections needed in order to have a complete mesh configuration?

# of links = 6 (6 - 1) / 2 = 15 links# of links = 6 (6 - 1) / 2 = 15 links

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Mesh topology Advantage:

Dedicated links guarantees own data load Robust Privacy/Security Easy fault isolation

Disadvantage Amount of cabling and no. of I/O ports

required Difficult installation and reconnection Expensive

Basic Topologies

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Star topology Each device has a dedicated point-to-point link

only to a central controller, usually called a HUB.

Basic Topologies

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Bus topology One long cable acts as a backbone to

link all the devices in a network

Basic Topologies

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Ring topology Each device has a dedicated point-to-point

connection with only the two devices on either side of it.

Basic Topologies

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Ring topology Advantage:

Orderly Performs better than bus topology Does not require network server

Disadvantage Failure of a single node, failure of entire

network Sensitive to node changes

Basic Topologies

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Hybrid (Tree) topology The topology in which a central 'root' node is

connected to one or more other nodes that are one level lower in the hierarchy.

Basic Topologies

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Star topology Advantage:

Easy to install and reconfigure Less cabling needed Robust Simplicity of operation

Disadvantage Dependency on one single point Possible slow down of network

Basic Topologies

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Hybrid (Tree) topology Advantage:

Supported by hardware vendors P2P connection is possible Ease of node access

Disadvantage Length of network depends of the type of

cable Entirely dependent on the trunk Difficult to configure

Basic Topologies

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Bus topology Advantage:

Easy to implement and extend Easy to install Cost effective Simplicity of operation

Disadvantage Difficult reconnection and fault isolation Dependency on the bus Limited cable length and number of stations

Basic Topologies

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Chapter 11. What is the difference between audio to

text, numbers and images? 2pts

2. What are the 3 characteristics of a network?

3. Consider a mesh network with 7 nodes, calculate how many cable connections needed in order to have a complete mesh configuration?

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The category into which a network falls is determined by its size.

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Local Area Network (LAN) connects nodes in a limited

geographical area normally covers an area less than 2 mi. e.g. home, school, computer lab, office

bldg. uses Ethernet cables, switches and hubs

Categories of Networks

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Metropolitan Area Network (MAN) larger than a LAN but smaller than a

WAN normally covers a town or a city connects nodes for high-speed

connectivity e.g. DSL internet connection, cable

internet connection

Categories of Networks

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Wide Area Network (MAN) spans a large physical distance Internet is the largest WAN is not owned by any one organization use technology like ATM, Frame Relay

and X.25

Categories of Networks

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Heterogeneous Network

Categories of Networks

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Interconnection of Networks:

Internetwork

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History 1960’s US government seeks nuclear war proof

communications, created ARPA 1969 Universities and researches connected to

ARPAnet In 1972, Vinton Cerf and Robert Kahn

collaborated for the Internetting Project In 1977 ARPAnet engineers devised a

communication protocol known as TCP/IP 1983 ARPAnet switched to TCP/IP 1989 Tim Berners-Lee proposes a new set of

Internet protocols 1995 US government releases Internet for

commercial use

Internet

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A protocol is a set of guidelines or rules.

A technical standard is an established norm or requirement.

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Protocols rules determining the format and

transmission of data key elements of a protocol:

syntax semantics Timing/synchronization

Protocols and Standards

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Standards provide guidelines to create and maintain an

open competitive market categories:

De Facto De Jure

Standards Creation Committees International Organization for Standardization (ISO) International Telecommunication Union (ITU) Consultative Committee for International Telegraphy

and Telephony (CCITT) American National Standard Institute (ANSI) Institute of Electrical and Electronics Engineers (IEEE) Electronics Industries Association (EIA)

Protocols and Standards

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Standards Forums

made up of representatives from interested corporations

test, evaluate and standardized new technologies present their conclusion to standards bodies

Regulator Agencies communication technology is regulated by

government agencies protect public interest by regulating radio, TV & cable Federal Communications Commission (FCC) - USA National Telecommunication Commission (NTC) - PHIL

Protocols and Standards

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End of Chapter 1

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Chapter Questions:Q.1) Which of the following are types of computer networks? A. LAN, NAN, WAN B. WAN, ring, star, bus C. old boys' network, old girls' network, business associates D. extranet, intranet, LAN, WAN Q.2) Which of the following is the best description of the transmission directions possible in a network? A. simplex, half-duplex, full duplex B. simplex, half-duplex, full duplex, duplex C. half duplex, 2/3 duplex, full duplex D. duplex, half duplex, 1/4 duplex Q.3) Which of the following is NOT a list of network topologies? A. star, bus, ring B. star, ring, hybrid C. bus, ring, double ring, hexagon D. ring, mesh, star, bus, Q.4) Which network topology has a central device which brings all the signals together? A. bus B. star C. ring D. hybrid Q.5) Which network topology requires terminators at the ends of the lines? A. ring B. bus C. star D. mesh Q.6) A blank is a number of computers linked together to allow them to share data and/or other resources. ( 2 words or 1 word )

Q.7) All communication systems must have a sender, a receiver and a blank. ( 2 words or 1 word ) Q.8) What is being described here -> pairs of copper wires twisted around each other. ( 3 words or 2 words )

Q.9) This cable uses light to transmit data instead of magnetic signals. ( 3 words or 2 words or 1 word ) Q.10) A blank converts digital signals to analogue signals and also analogue signals to digital signals . ( 1 word )

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Chapter Questions:

1. Identify the five properties of a data communications system.

2. Name four basic network topologies, and cite an advantage of each.

3. Why are protocols needed?