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1Dr. L. Christofi Fall 2007

Lecture 1

Introduction

Network ModelsMSCEG 425

Data & Computer Communications

Data & Computer CommunicationsData & Computer CommunicationsData & Computer Communications

Fall 2007

2Dr. L. Christofi Fall 2007

0. Overview0. Overview

In this lecture we will cover the following topics:

1.Introduction

1.1 Introduction to data communications and networks

1.2 Networks

1.3 The Internet

1.4 Protocols & Standards

1.5 Summary (part 1)

2.Network Models

2.1 Layered tasks

2.2 OSI model

2.3 Layers in the OSI model

2.4 TCP/IP protocol suite

2.5 Addressing

2.6 Summary (part 2)

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3Dr. L. Christofi Fall 2007

1.0 INTRODUCTION1.0 INTRODUCTION1.0 INTRODUCTION1.0 INTRODUCTION1.0 INTRODUCTION1.0 INTRODUCTION1.0 INTRODUCTION1.0 INTRODUCTION

The term The term telecommunicationtelecommunicationmeans communication at a means communication at a

distance. distance.

The word The word datadatarefers to information presented in whatever refers to information presented in whatever

form is agreed upon by the parties creating and using the form is agreed upon by the parties creating and using the

data. data.

Data communicationsData communicationsare the exchange of data between two are the exchange of data between two

devices via some form of transmission medium such as a wire devices via some form of transmission medium such as a wire

cable. cable.

Components

Data Representation

Data Flow

Topics discussed in this section:Topics discussed in this section:

4Dr. L. Christofi Fall 2007

Components of data communication

A data communication system has 5 components:

-Message: info (data) to be communicated -Sender: device that sends the data message -Receiver: device that receives the message -Medium: transmission medium (physical path) by which a message travels from the transmitter to the receiver -Protocol: set of rules that governs data communications 1.#

5Dr. L. Christofi Fall 2007

Data representation

•Text: bit pattern •ASCII: 128 different symbols (7 bits) •Extended ASCII: size of each pattern is 1 byte (8 bits) •Unicode: 65.536 symbols (16 bits) •ISO: 4.294.967.296 symbols (32 bits) •Numbers: decimal numbers converted directly to binary •Images: divided into a matrix of pixels •Audio: representation of sound by an analog or a digital signal •Video: represented by an analog or digital signal

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Direction of data flow

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7Dr. L. Christofi Fall 2007

1.2 NETWORKS1.2 NETWORKS

A A networknetworkis a set of devices (often referred to as is a set of devices (often referred to as

nodesnodes) connected by communication ) connected by communication linkslinks. . A node can be a computer, printer, or any other A node can be a computer, printer, or any other

device capable of sending and/or receiving data device capable of sending and/or receiving data

generated by other nodes on the network.generated by other nodes on the network.

Network Criteria

Physical Structures

Categories of Networks

Topics discussed in this section:Topics discussed in this section:

8Dr. L. Christofi Fall 2007

Network criteria

•Performance -Can be measured in may ways •transit time: amount of time required for a message to travel from one device to another •response time: time elapsed between an inquiry and a response •Number of users •Type of transmission medium •Hardware capabilities and software efficiency •Reliability -A measure of frequency of failure and the time needed to recover, network robustness •Security -Protecting of data from unauthorized users 1.#

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Physical StructuresPhysical StructuresPhysical StructuresPhysical Structures Types of connections: point-to-point and multipoint

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Physical Topology

Physical topology refers to the way in which a network is laid out physically. Network topology is the geometric representation of the relationship of all the links and linking devices (nodes) 1.#

11Dr. L. Christofi Fall 2007

Topology categoriesTopology categoriesTopology categoriesTopology categories

Number of links = n*(n-1)/2

MeshStar

Number of links = n

Bus

Number of links = n+1

Ring

Number of links = n

12Dr. L. Christofi Fall 2007

A hybrid topology A hybrid topology A hybrid topology A hybrid topology A star backbone with three bus networks

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13Dr. L. Christofi Fall 2007

Categories of networks

•Local Area Networks (LANs) -Usually privately owned and links the devices in a single office, building or campus -Most common LAN topologies are bus, ring and star -Speeds of 100Mbps-1Gbps •Metropolitan Area Networks (MANs) -Designed to extend over a city -May be owned by a large private organization or a service provider (telephone company) •Wide Area Networks (WANs)

-Provide long-distance transmission of data, voice, image and video info over large geographical areas that may comprise a country or a continent

•Internetworks -When two or more networks are connected they become an internetwork or internet

14Dr. L. Christofi Fall 2007

WAN examplesWAN examplesWAN examplesWAN examples

A switched WAN and a

point-to-point WANAn heterogenous network made of 4 WANs and 2 LANs 1.#

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An heterogeneous network An heterogeneous network An heterogeneous network An heterogeneous network made of four WANs and two LANs

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Comparison of LANs, MANs, & WANs

LANs:1 - 1000 Mbps

MANs:10 - 40 Gbps

WANs:Tbps

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17Dr. L. Christofi Fall 2007

1.3 THE INTERNET1.3 THE INTERNET1.3 THE INTERNET1.3 THE INTERNET1.3 THE INTERNET1.3 THE INTERNET1.3 THE INTERNET1.3 THE INTERNET

The The InternetInternethas revolutionized many aspects of our daily has revolutionized many aspects of our daily

lives. lives.

It has affected the way we do business as well as the way we It has affected the way we do business as well as the way we

spend our leisure time. spend our leisure time.

The Internet is a communication system that has brought a The Internet is a communication system that has brought a

wealth of information to our fingertips and organized it for ourwealth of information to our fingertips and organized it for our

use. use.

A Brief History

The Internet Today (ISPs)

Topics discussed in this section:Topics discussed in this section:

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A brief history

•Mid-1960s -Standalone devices

-ARPA (Advanced Research Projects Agency) was interested in finding a way to connect computers to share information

-Backbones: None - Hosts: None •1967 -ARPA presented its ideas for ARPANET -Backbones: None - Hosts: None •1969 -The first physical network was constructed -Backbones: 50Kbps ARPANET - Hosts: 4 •1972 -The first e-mail program was created by Ray Tomlinson of BBN -Backbones: 50Kbps ARPANET - Hosts: 23 •1973 -Development began on the protocol later to be called TCP/IP (by Vint Cerf and Bob Kahn) -Backbones: 50Kbps ARPANET - Hosts: >23 1.#

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Hierarchical organization of Internet

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The Internet today (ISPs)

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1.4 PROTOCOLS AND STANDARDS1.4 PROTOCOLS AND STANDARDS

In this section, we define two widely used terms: In this section, we define two widely used terms: protocolsprotocols

and and standardsstandards. First, we define protocol, which is . First, we define protocol, which is

synonymous with rule. Then we discuss standards, which synonymous with rule. Then we discuss standards, which

are agreedare agreed--upon rules.upon rules.

Protocols

Standards

Standards Organizations

Internet Standards

Topics discussed in this section:Topics discussed in this section:

22Dr. L. Christofi Fall 2007

Protocols

•A protocol is a set of rules that governs data communications •It defines whatis communicated, howit is communicated and whenit is communicated •Key elements of a protocol: -Syntax •Structure or format of data, meaning the order in which they are presented -Semantics •Refer to the meaning of each section of bits, how a particular pattern is interpreted and what action to be taken -Timing •Refers to when data should be sent and how fast can they be sent 1.#

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Standards

•Standards are essential in creating and maintaining an open and competitive market for equipment manufacturers

•Required to guarantee national and international interoperability of data and telecommunications technology and processes

•Categories of data communications standards -De facto: •Standards that have not been approved by an organizational body but have been adopted through widespread use, eg. model TCP/IP) -De jure: •Those that have been legislated by an official recognized body, eg.

OSI model

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Standards organizations

•Standards creation committees -ISO (International Organization for Standardization) -ITU-T (International Telecommunications Union - Telecommunications

Standards)

•Initially known as CCITT (Consultative Committee for International

Telegraphy and Telephony)

-ANSI (American National Standards Institute) -IEEE (Institute of Electrical and Electronics Engineers) -EIA (Electronic Industries Association •Forums -Made up of representatives from interested corporations to speed acceptance and use of new technologies in the telecom industry •Regulatory Agencies -Governmental agencies: to protect public interest by regulating radio,

TV and wire/cable communications

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25Dr. L. Christofi Fall 2007

Internet standards

•An Internet standard is a thoroughly tested specification used by those who work with the

Internet

•A specification begins with an Internet draft -Working document with no official status and a 6-month lifetime -Upon recommendation from the Internet authorities a draft may be published as a Request for Comment (RFC)

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1.5 SUMMARY (part 1)

•Data communication is the transfer of data from one device to another via some form of transmission medium.

•A data communications system must transmit data to the correct destination in an accurate and timely manner.

•The five components that make up a data communications system are the message, sender, receiver, medium, and protocol.

•Text, numbers, images, audio, and video are different forms of information.

•Data flow between two devices can occur in one of three ways: simplex, half-duplex, or full-duplex.

•A network is a set of communication devices connected by media links.

•In a point-to-point connection, two and only two devices are connected by a dedicated link. In a multipoint connection, three or more devices share a link.

•Topology refers to the physical or logical arrangement of a network. Devices may be arranged in a mesh, star, bus, or ring topology.

•A network can be categorized as a local area network (LAN), a metropolitan-area network (MAN), or a wide area network (WAN).

•A LAN is a data communication system within a building, plant, or campus, or between nearby buildings.

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