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Chapter 1

Introduction

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Impact of Data Communications

and Networking

Immediate access to information

Quicker decision making

Accuracy

Efficiency

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Data Communication

What is Data?

What is Communication?

Communications vs. Telecommunications

Characteristics of effectiveness in data communication:

Delivery: to intended destination

Accuracy: immunity to noise and alteration

Timeliness: reduced delays (application dependent)

Jitter: variation in the delivery time

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Concepts of Data Communication

Components

Data Representation

Direction of Data Flow

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Figure 1.1 Five components of data communication

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Data Representation

Text: represented using bit patterns

ASCII: 7-bit (128 symbols)

Extended ASCII: 8-bit (256 symbols)

Unicode: 16-bit (65,536 symbols)

ISO: 32-bit (4B symbols)

Numbers: represented in binary

Images: bit patterns for pixels and colors

Audio: analog or digitized form

Video: analog or digitized form

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Types of Data Flow

Simplex: one direction

Single link

Examples: keyboard and terminal

Half-Duplex: either direction with time sharing

Single link

Example: Walkie-Talkie

Full-Duplex: both directions at the same time

Single link with shared bandwidth or dual link

Example: telephone network

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Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

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Networks

What is a network?

Set of devices or nodes connected via communication links

Networking Concepts:

Distributed Processing

Network Criteria

Physical Structures

Network Models

Categories of Networks

Interconnection of Networks: Internetwork

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Distributed Processing

Decentralized processing

Tasks are processed by several nodes

Example: Web pages are centrally and remotely stored but locally processed

Overhead of distributed processing

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Network Criteria

Performance

Bit rate vs. packet rate vs. throughput (effective bit rate)

Transit time (or propagation delay)

Response time (round trip delay)

Reliability

Bit error rate vs. packet error rate

Error detection and correction

Link failure recovery time

Robustness to disasters

Security

Protect against unauthorized access

Protect against alteration

Validity of sender

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Types of Network Connections

Point-to-point link

Dedicated link between two nodes

Full link capacity

Multi-point link

Shared link among many nodes

Spatially shared: simultaneous access

Temporally shared: timely shared

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Figure 1.3 Types of connections: point-to-point and multipoint

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Figure 1.4 Categories of topology

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Figure 1.5 A fully connected mesh topology (five devices)

Point-to-point

n(n-1)/2 dedicated links

(n-1) I/O ports per device

Advantages:

Full capacity

Robustness (one link failure does not bring down whole network)

Privacy and security

Easy fault detection and isolation

Disadvantages:

Cabling (installation) overhead

I/O ports

Space

Cost

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Figure 1.6 A star topology connecting four stations

Point-to-point to the hub

Indirect connections among the nodes

n dedicated links to a hub

1 I/O port per device

Advantages:

Robustness

Easy fault detection and isolation

Disadvantages:

Single point of failure at the hub

Bottleneck at the hub

store-and-forward (in case of a switch)

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Figure 1.7 A bus topology connecting three stations

Multi-point

1 backbone link

1 I/O port per device

Advantages:

Ease of installation

Minimum cabling at installation

Disadvantages:

Limited taps and distance to node

Limited node addition after initial installation

Limited quality due to signal reflection at taps

Difficult fault isolation

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Figure 1.8 A ring topology connecting six stations

Point-to-point

n dedicated links

2 I/O ports per device

Advantages:

Easy installation

Easy fault detection and isolation

Disadvantages:

Speed: store-and-forward at each node

Ring length and number of nodes

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Figure 1.9 A hybrid topology: a star backbone with three bus networks

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Categories of Networks

Personal Area Network (PAN)

Local Area Network (LAN)

Metropolitan Area Network (MAN)

Wide Area Network (WAN)

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LAN

Privately owned

Single office, building, or campus

Used for shared resources

Hardware (e.g. printer, scanner, etc)

Software (e.g. engineering application)

Data (e.g. specifications, drawings, etc.)

Data rates up to gigabits per second

Size is limited to a few kilometers

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LAN (Continued)

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Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

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MAN

Spans an entire city

Single large network

Telephone network (public)

LAN-to-LAN connection

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Figure 1.15 WAN

May spans the entire globe

Long distance transmission

May use public, leased, or private networks and equipment

The concept of an enterprise network

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The Internet

DefinitionImpactA Brief HistoryThe Internet Today

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Definition

An internet: two or more networks that can communicate with each other

The Internet: the network of all networks

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Impact of the Internet

Revolution of communications and information exchange

eCommerce

eLearning

eMail

eGovernment

etc.

Created a very well-connected world

Near real-time access to resources

Changed the ways people live

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History of the Internet

Mid 1960’s: ARPA (Advanced Research Projects Agency) of DOD (Department of Defense)

ARPANET was initiated in 1967 and done in 1969

Interface Message Processors

Network Control Protocol

4-node internetwork

1972: Internetting Project

1973: TCP (Transmission Control Protocol)

End-to-end packet delivery

Encapsulation, datagram, segmentation, reassembly, error detection, and gateway functionality

1973: IP (Internetworking Protocol)

Datagram routing

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Figure 1.13 Hierarchical organization of the Internet

All types of networks

Connected by switching devices

Continuously changing

Run by private companies

Local Internet Service Provider (ISP): direct service to end user

Regional ISP: provide service to ISP’s

National Service Provider (NSP): connecting private backbone networks

Network Access Point (NAP): connects NSP’s

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Protocols and Standards

ProtocolsStandardsStandards OrganizationsInternet Standards

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Definitions

A Protocol: a set of rules that governs data communications

Syntax: the structure or format of the data (e.g. how many bits for each section)

Semantics: the interpretation of the data bit patterns

Timing: when and how fast the data should be sent

A Standard: a set of agreed-upon rules that govern data communications

Interoperability

Open market for competition

Guidelines to manufactures, vendors, government agencies, and service providers

De Facto vs. De Jure standards

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Standard Organizations

Standards Creating Committees:

International Organization for Standardization (ISO)

International Telecommunication Union – Telecommunications Standards (ITU-T)

American National Standards Institute (ANSI)

Institute of Electrical and Electronic Engineers (IEEE)

Electronic Industry Association (EIA)

Forums (Special Interest Groups)

Regulatory Agencies (e.g. FCC)

Internet Standards:

Internet Draft: working document for 6 months

Request for Comment (RFC): recommended and published draft