Signals

1.1 Signal Wave Elements

All types of telephones use signals to transfer information and control the exchange of data. A signal, or signal wave, is the main element responsible for carrying information from a transmitter to a receiving medium. It is the energy that causes a circuit to perform its intended action, be it transmission or reception of messages and information.

A telephone is comprised of two major components: a transmitter and a receiver. Information is transferred from the transmitter to the receiver in the form of electromagnetic waves or pulse patterns, which travel through a transmission medium. These pulse patterns are called waveforms or signal waves. These signal waves, while travelling through space, can take on different shapes and lengths. They can be sinusoidal or sine, triangular, square, or sawtooth waves.

Like any other electromagnetic waves, the signal waves of telephones are comprised of several elements. These elements control the efficiency and intensity of the information being transferred. Signal wave elements include wavelength, period, velocity, frequency, and amplitude. These elements are shown visually in Diagrams 1.1(i) and 1.1(ii), respectively.

The elements shown in Diagrams 1.1(i) and 1.1(ii) are defined as below:

i. Amplitude -The maximum displacement of a wave from its equilibrium position.

ii. Period -The time takes to make one complete wave cycle.

iii. Frequency -The number of wave cycles made in one second

iv. Wavelength -The distance between two consecutive points on a wave that propagates at the same phase

Many may think that signals existed only after the advent of electronic communication and the invention of various types of telecommunication devices, but they are mistaken. In fact, the use of signals can be traced back since the long distance communication among people began. Signals have always been a crucial part of communication, particularly communication over long distances. In the past, signals come in the form of smoke, sound, and drawings. Sending notes using birds as well as lighting up fires at night were also widely used. In today's modern society, these manners of sending signals are long gone, replaced by more modern methods. With the advent of new breakthroughs in technology that started with the invention of the first telephone in the 1800s up to the time of contemporary telecommunication systems in this new era, signals are now classified as analog or digital.

1.2 Analog Signal

Analog signal is a type of signal wave that is common in most sounds. It is continuous and contains time-varying quantities. The changes of its physical properties and the different values in its waveform have a smooth transition, producing sounds that have no breaks or interruptions. Data from analog signal waves are transferred by means of analog communication channels, such as a wire or cable line media and radio frequency waves. Diagram 1.2 shows a coherent analog signal graph.

Analog signal is commonly used in a variety of applications, the most common of which include the following:

i. Frequency Modulation (FM) radio broadcasting

ii. Aerial television broadcasting

iii. Walkie-talkie or handheld transceiver communication

iv. Amateur radio or ham radio

v. Sound Navigation and Ranging (Sonar)

vi. Radio Detection and Ranging (Radar)

1.3 Digital Signal

Digital signal is a type of signal wave that is transmitted as a pattern of bits. It consists of pulse trains that rapidly change between two levels of intensity. The digital signal can be one of two values, such as 1V for maximum levels and 0V for minimum levels. Unlike analog signal, digital signal is disrupted and has a stepping appearance. It may also be square and discrete. The discrete appearance is due to the signal trying to approximate values. At a distance, the stepping appearance may not be readily perceptible and the pulse variations of the signal wave may look analog and smooth. Up close, though, the discrete steps of the signal may become visible. Diagram 1.3 shows a digital signal graph with continuous pulse variations.

Digital signal is also used in a number of varied applications. These include Auto Tele Machine (ATM), Global Positioning System (GPS), Electronic mail, and E-Commerce.

1.4 Comparison Between Analog and Digital Signals

Both analog and digital signals are transmitted electronically through a transmission medium. Their differences lie on their varied characteristics, as discussed below:

i. Analog Signal

a. Appears as a continuous wave form with variable amplitude.

b. Vulnerable to noise interference during the transmission process

c. Restoration of the original signal transmitted is not feasible.

d. Information is presented in sine wave form.

ii. Digital Signal

a. Information is represented by square waves and transmitted in discrete values as 0 and 1.

b. Can be immune to noise during the transmission process

c. Allows easy restoration of original signals

Signaling

2.1 Overview of Signaling

Signaling is the process of sending signal throughout networks. This process is an important aspect in the telephone industry and telecommunications in general. Without signaling it would be difficult to transfer information from one point to another. In a nutshell, signaling can be said as nerve of any telecommunication networks, particularly in the complex mechanisms of telephones.

Signaling is basically the progression of a moving element from one place to another. In the context of telecommunications, the moving element can be voice or speech transmitted through a wired or wireless communications channel. A standard signaling block diagram is shown in Diagram 2.1

In a standard telephone network, signaling is the process of exchanging information for the purpose of establishing, maintaining, and terminating telephone call connections. Three categories of signaling are used in telephone networks. These are the following:

i. User to network node signaling.

a. A type of signaling used to ensure the standby, establishment, and active status of telephone calls.

ii. Inter-network node...