1-1 Business Data Communications and Networking, 6 th ed. FitzGerald and Dennis

1-2 Copyright © 1999 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without the express written permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for redistribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein.

1-3 Introduction to Data Communications Chapter 1

1-4 Objectives Become familiar with… u the history of communications and information systems, u the applications of data communication networks, u the major components of networks, u the importance of standards, u three key trends in communications and networking, Understand the role of network layers.

1-5 INTRODUCTION

1-6 Why Study Data Communications? The key technology of the information age is communications. Data communications and networking is a truly global area of study, both because the technology enables global communication, and because new technologies and applications often emerge from a variety of countries and spread rapidly around the world.

1-7 DATA COMMUNICATIONS NETWORKS

1-8 Data Communications u Data Communications The movement of computer information from one point to another by means of electrical or optical transmission systems. Such systems are often called data communications networks. u Telecommunications Includes the transmission of voice and video as well as data.

Analog and Digital Data Transmission u Digital Signals are electrical pulses generated by a computer or a terminal (binary: on- off) u Analog signals are audio tones into which the digital signals are converted for transmission in a telephone network (wave: numerous values) u A modem is a device which converts the direct electrical signals produced by the computer (positive and negative voltages of electricity) to modulated audio signals that can be sent over telephone communications circuits u Connector cable connects the modem to the micro computer (or a terminal) ©Jaana Porra 2001

Using Telephone Networks (Analog) for Data Communications (Digital) u Local loop: In a telephone network, the “last mile” which connects home or office to telephone company’s central office u Central Office, end office or Exchange office contains the switching facilities operated by the telephone company. u Private Leased Circuit refers leasing a private circuit path and bypassing switching at the central office u Interchange Channels/Circuits (IXC) are the circuits that go from one telephone company central office to another central office (coaxial, fiber, satellite etc.) u Common Carrier is a company recognized by FCC or an appropriate state licensing agency as having the right to furnish telecommunications services to individual subscribers or business organizations ©Jaana Porra 2001

1-11 Components of a Network u Server (or Host computer) Central computer in the network, storing data or software that can be accessed by the clients. u Client The input/output hardware device at the other end of a communications circuit. u Circuit The pathway through which the messages travel.

1-12 Components of a Network

Computer Networks in a Nutshell B A C K B O N E BACKBONE LAN M E T R O P O L I T A N AREA NW WIDE AREA NETWORK B A C K B O N E BACKBONE Corporation 1, Town 1 Corporation 2, Town 2 ©Jaana Porra 2001

Intranet, Internet, Extranet in a Nutshell I N T R A N E T INTRANET INTERNET I N T R A N E T INTRANET E X T R A N E T EXTRANET ©Jaana Porra 2001

1-15 Types of Networks Networks can be classified in many different ways. One of the most common is by geographic scope: Local Area Networks (LAN) Backbone Networks (BNs) Metropolitan Area Networks (MANs) Wide Area Networks (WANs)

1-16 Types of Networks

1-17 Types of Networks u Local Area Networks (LAN) A group of microcomputers of terminals located in the same general area and connected by a common circuit. Covers a clearly defined small area, such as within or between a few buildings, Support data rates of 10 to 100 million bits per second (Mbps).

1-18 Types of Networks u Backbone Network (BN) A larger, central network connecting several LANs, other BNs, metropolitan area networks, and wide area networks. Typically span up to several miles. Support data rates from 64 Kbps to 45 Mbps.

1-19 Types of Networks u Metropolitan Area Network (MAN) Connects LANs and BNs located in different areas to each other and to wide area networks. Typically span from miles. Supports data rates of 100 to 1000 Mbps.

1-20 Types of Networks u Wide Area Network (WAN) Connects BNs and MANs and are usually leased from inter-exchange carriers. Typically span hundreds or thousands of miles. Supports data rates of 28.8 Kbps to 2 Gbps.

Some Network Architectures u Peer-to-Peer network is a computer network in which computers function as equals u Hierarchical Network is a computer network which is controlled by a central computer often called the host computer u Point-to-point network connects two points (e.g., a micro computer to a server) u Broadcast network (one-to-many) connects one point (e.g., a server) to many (e.g., a host computer to micro computers) ©Jaana Porra 2001

Connecting Network Nodes u Circuit is the pathway through which the messages travel (copper wire, fiber optic cable, wireless transmission) u Bridge is a device that connects two similar networks using the same data link and network protocols. u Gateway is a device that connects two dissimilar networks and allows two networks of different vendors to communicate by translating one vendor’s protocol into another. u Router is a device that connects two similar networks which have the same network protocol. It also chooses the best route between two networks when there are multiple paths between them. u Brouter is a device which combines the functions of a bridge and a router. u Repeater is a device used to boost the strength of a signal. Repeaters are spaced at intervals throughout the length of a communication circuit. ©Jaana Porra 2001

Establishing a Connection u Protocol is a formal set of conventions governing the format and control of inputs and outputs between two communications devices. This includes the rules by which these two devices communicate as well as handshaking and line discipline u Handshaking is the exchange of predetermined signals when a connection is established between two data devices. This is used to establish the circuit and message path. u Session is the logical connection between two terminals. This is the part of the message transmission between two points after the communications circuit has been established and is functioning. ©Jaana Porra 2001

Client-Server in a Nutshell 1. Fill-in-the Blanks User Interface 2. Distributed Presentation Management 3. Application to Application Interface 4. Distributed Data Access 5. Physical File Server 6. Local Processing Data Files Data Base Man. SQL Flat File Application Dialog or Presentation Manager ©Jaana Porra 2001

1-25 NETWORK MODEL

1-26 Network Model A method of describing and analyzing data communications networks, by breaking the entire set of communications functions into a series of layers, each of which can be defined separately. This allows vendors to develop software and hardware to provide the functions separately.

1-27 Networking Model Open System Interconnection (OSI) Model, developed in 1984, helped change the face of network computing. Other models like TCP/IP have become more prominent in the design of networks and network technology.

International Organization for Standardization (ISO) Open Systems Interconnection (OSI) Reference Model APPLICATION PRESENTATION SESSION Application Services are Provided by the Upper Layer Infrastructure TRANSPORT NETWORK DATA LINK PHYSICAL End-to-End Services are Provided by the Lower Layer Infrastructure ©Jaana Porra 2001

The OSI Reference Model Continued APPLICATION PRESENTATION SESSION TRANSPORT NETWORK DATA LINK PHYSICAL Manages the communication between applications Adds structure to the exchanged data units Adds control mechanisms to exchanged data Transfers and multiplexes data reliably across the network Transfers data over the network independent of media and topology of subnetworks Transfers data over a single communications link, does framing and error control Responsible for the electro-mechanical interface to the communications media A letter mailed and received The envelope layout Address, return address postage on envelope The US Postal Service The Postal Service ground and air transportation network A mail truck from post office to airport The truck ©Jaana Porra 2001

A 4-Layer Model APPLICATION NETWORK DATA LINK PHYSICAL APPLICATION NETWORK DATA LINK PHYSICAL Application software used by the network user Translates and routes the message; collects accounting information Controls the physical layer; formats the message detects and corrects errors The physical connection between sender and receiver ©Jaana Porra 2001

1-31 Networking Model

1-32 Simplified Network Model u Application layer (Layer 4) The application software used by the network user, allows the user to define what message are sent over the network.

1-33 Simplified Network Model u Network layer (Layer 3) Takes the message generated by the application layer and performs three functions before passing them to the data link layer. 1. Translates the destination of the message into an address understood by the network. 2. If multiple routes possible, it decides which routes to take. 3. Collects message accounting information that can be used to identify how many messages each user has sent and to track errors.

1-34 Simplified Network Model u Data link layer (Layer 2) Takes the message generated by the network layer and performs three functions before passing the message on the physical layer. 1. It controls the physical layer by deciding when to transmit messages over the media. 2. It formats the message by indicating where messages start and end, and which part is the address. (It may break it into smaller packets). 3. It detects and corrects any errors that have occurred in the transmission of the message.

1-35 Simplified Network Model u Physical layer (Layer 1) The physical connection between the sender and receiver. It transfers a series of electrical, radio, or light signals through the circuit from sender to receiver. It specifies the type of connection, and the signals that pass through it.

1-36 Network Models For Communications to be successful, each layer in one computer must be able to communicate with its matching layer in the other computer. This is accomplished by standards.

1-37 NETWORK STANDARDS

1-38 The Importance of Standards Standards are necessary in almost every business and public service entity. The primary reason for standards is to ensure that hardware and software produced by different vendors can work together. The use of standards makes it much easier to develop software and hardware that link different networks because software and hardware can be developed one layer at a time.

1-39 The Standards Making Process Two types of standards: Formal standards are developed by an official industry or government body. Defacto standards emerge in the marketplace and supported by several vendors, but have no official standing.

1-40 The Standards Making Process Formal standardization process has three stages 1. Specification stage: developing a nomenclature and identifying the problems to be addressed. 2. Identification of choices stage: those working on the standard identify the various solutions and choose the optimum solution from among the alternatives. 3. Acceptance, the most difficult stage: defining the solution and getting recognized industry leaders to agree on a single, uniform solution

1-41 Telecommunications Standards Organizations u International Organization for Standards (ISO) Member of the ITU, makes technical recommendations about data communications interfaces.

1-42 Telecommunications Standards Organizations u International Telecommunications Union - Telecommunication Standardization Sector (ITU-TSS) Technical standard setting organization of the UN ITU. Formerly called the Consultative Committee on International Telegraph and Telephone (CCITT) Comprised of representatives of over 150 Postal Telephone and Telegraphs (PTTs), like AT&T, RBOCs, or common carriers.

1-43 TC Standards Organizations American National Standards Institute (ANSI) Institute of Electrical and Electronics Engineers (IEEE) Electronic Industries Association (EIA) National Institute of Standards and Technology (NIST) National Exchange Carriers Association (NECA) Corporation for Open Systems (COS) Electronic Data Interchange -(EDI) of Electronic Data Interchange for Administration Commerce and Transport (EDIFACT).

1-44 FUTURE TRENDS IN COMMUNICATIONS AND NETWORKING

1-45 Future Trends Between now and the year 2010, data communications will grow faster and become more important than computer processing itself. There are three major trends driving the future of communications and networking: Pervasive Networking The Integration of Voice, Video and Data New Information Services

1-46 Pervasive Networking In the future, communications networks will be everywhere. This pervasive networking means that virtually any computer will be able to communicate with any other computer in the world. This will increase telecommuting in which employees perform some or all of their work at home instead of going to the office each day.

1-47 Pervasive Networking Cellular telephone networks will begin to compete directly with the current wired telephone network. Pervasive networking will also increase the use of electronic data interchange (EDI), the paperless transmission of business documents between companies. The Internet has experienced such rapid growth that it now connects millions of computers in virtually every country in the world.

1-48 The Integration of Voice, Video and Data The integration of voice and data is largely complete in wide area networks. The integration of video into computer networks has been much slower, partly due to past legal restrictions, and partly due to the immense communications needs of video.

1-49 New Information Services The World Wide Web has changed the nature of computing so now that almost anyone with a computer can be their own publisher. Never before in the history of the human race has so much knowledge and information been available to ordinary citizens.

1-50 End of Chapter 1

End of Lecture 2! © 2001 Jaana Porra University of Houston