Analog vs. Digital Switching: Key Differences Explained

This article compares analog switching and digital switching, outlining the differences between the two technologies. It covers the basics of each, including their operational principles, to clearly illustrate the distinctions.

Introduction

Telecommunication systems facilitate the transmission of information from one terminal to another, as selected by the originator. A typical telecom system consists of four key elements:

• End terminals (e.g., telephones or mobile devices)
• Transmission system
• Switching system
• Signaling system

Figure 1 illustrates the components of a plain old telephone system (POTS), from the calling party to the called party.

The transmission system, whether wired or wireless, transports information in various forms, designed to withstand signal degradation. This link carries both user information (voice, data, messages, video) and signaling information, using guided or unguided mediums. Common examples of transmission systems include:

• Microwave links
• Satellite links
• Fiber optic lines
• Coaxial lines
• 2-wire transmission lines

The switching system provides various services to subscribers. It’s a collection of switching elements, arranged and controlled to establish a communication path between distant points or terminals.

• Switching systems are categorized as manual or automatic.
• Automatic switching systems are further divided into electro-mechanical and electronic types.
• Electro-mechanical switching includes Strowger (step-by-step) and crossbar switching.
• Electronic switching encompasses Time division switching, Space division, and space-time switching.
• Typical examples of switching systems include telephone exchanges, voice switches, gateways, routers, and network switches.

Based on the type of information being transported (voice, data, or messages), different switching mechanisms are employed, such as circuit switching, packet switching, and message switching, respectively.

Analog Switching

• Analog switching involves switching analog signals using analog switches.
• The system uses analog signals on both the line and trunk sides of the switch.
• Analog lines and/or trunks interface with digital systems using A/D (Analog-to-Digital) and D/A (Digital-to-Analog) converters, as needed.
• Analog switching systems require A/D and D/A converters to process digital signals.

Digital Switching

• Digital switching refers to switching digital signals using digital switches.
• Digital switches can communicate with each other via digital trunks while simultaneously supporting analog lines and analog trunks.
• There are no analog lines/trunks in a purely digital switching system. All communication between digital switches is carried out via digital signaling.

The figure above depicts various modules of a digital switching system. Line Modules (LMs) and Trunk Modules (TMs) are major building blocks. Other modules include Interface Controller (IC), switching fabric, Service Circuits (SC), Central Processor, and Network Control Processors.

Switching fabric refers to the switching matrix, used to switch lines and trunks under the control of the central processor and network controllers.

Analog Switching vs. Digital Switching: Key Differences

The following table highlights the key differences between analog switching and digital switching:

Summary

Analog switching involves routing continuous signals and is typically slower, whereas digital switching handles discrete signals, offering higher speed and efficiency. Digital switching systems also utilize memory to store call information, enhancing performance and functionality. Now-a-days analog switching has been replaced by digital switching. Few older analog systems still exist in some countries.