Introduction to Data Communications

Chapter 1


Become familiar with…

Understand the role of network layers.


Why Study Data Communications?

We have moved into an information society dominated by computers, data communications, and highly skilled individuals...

At no other time in our history, has success (whether individual, corporate, or national) depended so heavily on intelligence and information.

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.

A Brief History of Communications in the U.S.

A Brief History of Communications in the U.S.

A Brief History of Communications in the U.S.

A Brief History of Communications in the U.S.

A Brief History of Communications in the U.S.

Telecommunications Competition and Deregulation Act of 1996

Practically overnight, the local telephone industry in the U.S. went from a highly regulated and legally restricted monopoly to open competition.

Local service in the U.S. is now open for competition.

RBOCs are now permitted to provide long distance services.

A Brief History of Communications in the U.S.

The Internet has been a different story. Virtually all RBOCs, LECs, and IXCs, have aggressively entered the Internet market.

Today, there are more than 5000 Internet Service Providers (ISPs) who provide dial-in access to the Internet to millions of small business and home users.

A Brief History of Information Systems in the U.S.

A Brief History of Information Systems in the U.S.

As we move into the new century, the most important aspect of computing is networking.

Networks already have had a dramatic impact on the way business is conducted.


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.

Includes the transmission of voice and video as well as data.

Components of a Network

Central computer in the network, storing data or software that can be accessed by the clients.

The input/output hardware device at the other end of a communications circuit.

The pathway through which the messages travel.

Components of a Network

Components of a Network

Do not need a server or host, but are designed to connect similar computers which share their data and software with each other.

Microcomputer networks are connected by a hub and cables (circuit).

A router is used to connect two or more networks, enabling computers on one network to communicate with computers on other networks (e.g. the Internet).

Types of Networks

Networks can be classified in many different ways. One of the most common is by geographic scope:

Types of Networks

Types of Networks

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).

Types of Networks

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.

Types of Networks

Connects LANs and BNs located in different areas to each other and to wide area networks.

Typically span from 3 - 30 miles.

Supports data rates of 100 to 1000 Mbps.

Types of Networks

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.


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.

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.

Networking Model

Simplified Network Model

The application software used by the network user, allows the user to define what message are sent over the network.

Simplified Network Model

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.

Simplified Network Model

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.

Simplified Network Model

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.

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.


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.

The Standards Making Process

Two types of standards:

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

Telecommunications Standards Organizations

Member of the ITU, makes technical recommendations about data communications interfaces.

Telecommunications Standards Organizations

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.

TC Standards Organizations


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

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.

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.

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.

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.


End of Chapter 1