Unit 2

Lesson 1 - Communication and Signals

   Introduction

A signal is any change in a measurable condition that is used to represent information. There is an almost endless number of ways we can send signals; however, they all require that we use some sort of energy to make a change that can be detected by someone or something. We can make sounds, wave flags, post signs, or use hand gestures. All of these can convey information, as long as both the sender and recipient agree on the meaning of the signal.

If we want to move data between computers, we must use a signaling method that machines can easily understand and that can span distances. Thus, data networks use three types of electromagnetic energy--electricity, light, and radio waves--to transmit signals. We will discuss each of these later in this unit.

Regardless of the type of energy used to carry a signal, all signals can be categorized according to one of three basic characteristics:

Analog or digital

One-way (simplex) or two-way (duplex)

Timed (synchronous) or not timed (asynchronous)

In this lesson, we explain each of these characteristics and discuss what they mean for data networking.

   Objectives

At the end of this lesson you will be able to:

1.

Describe the difference between baseband and broadband signaling

2.

Explain why a computer needs a modem to communicate over a telephone line

3.

Describe bandwidth and how it is measured

4.

Explain why standards are required for signaling, and name some of the most important organizations that make standards for network communication

Key Point
Baseband (digital) signaling is predominantly used in data networks.


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