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To meet the needs of telephone customers, modem switching systems are designed to perform four major functions - Call Processing, Administration, customer service and Maintenance. Call Processing comprises all necessary tasks to connect one telephone to another. These tasks include Supervision while Administration involves monitoring and recording of the system and customer-related conditions. System administration functions include rerouting of network traffic to avoid congestion and reporting traffic data to measure telephone patterns at certain times or areas of network. Customer-related features include recording information about toll calls for billing purposes.

Maintenance involves detection and correction of trouble in the switching system to insure reliable and efficient operation. Maintenance functions include automatic detection and isolation of a problem and, in some cases, location of the trouble while customer service involves the additional features that expand a customer’s telephone service, and are provided by most modern switching system. These features include call-forwarding, conference calls, speed dialing, directory assistance, and special business services, such as Centrex.

Signaling is the common language by which switching machines communicate. In addition to transmitting information, telephone networks also transmit control signals. These signals are transmitted between network control devices, which enable them to set up, disconnect and control the transmissions. Many such supervisory signals are needed to set up a call through a complex network.

Analog ESS perform line and/or trunk connections that are in analog form when they pass through the switch while the Digital ESS connects lines and/or trunk circuits that convert the analog signals into digital form when they pass through the switch.The digital ESS is more efficient than the analog ESS because it has electronic components that are more reliable, less expensive, and faster than the electro-mechanical devices used in the analog ESS. It requires conversion of analog lines to digital lines only at end offices. It handles more complex signaling data, which increases the processing speed and provides more customer services. It directly accommodates signals for many services, such as fax, video and data transfer. It is designed in a flexible, modular manner that can be easily expanded or modified.

Signaling is the common language by which switching machines communicate. In addition to transmitting information, telephone networks also transmit control signals. These signals are transmitted between network control devices, which enable them to set up, disconnect and control the transmissions. Many such supervisory signals are needed to set up a call through a complex network. There are three classes of signaling that are frequently used - Altering Indicators which inform the customer of call-processing conditions, Inter-office Trunk Signals which are used to exchange information between switching machines and special Services Signals which enable custom telephone features to be implemented by pressing pre defined keys on the telephone set.

Electronic Switching Systems offer a great potential for voice and data communications. An ESS consists of Computer Memory and Rapid Switching Component. Switching systems are programmed to handle various situations and perform specialized functions. Additional features can be added by modifying the program that controls the switching system. All switching equipments have two basic units such as the Control Unit and the Switching Unit.

The control unit is the brain of the switching system. It can switch a call in a fraction of a second, and therefore can service many stations and lines. The control unit receives and stores digital pulses. It interprets the digital pulses and selects an available path through the switching hardware to complete a connection. Efficient high speed control equipment can complete many calling connections during the time of conversation.

An important advantage of an ESS is the ability of the computer to analyze the traffic situation and reroute the call. It can also perform telephone-related accounting functions. There are two types of Electronic Switching Systems called the Analog ESS and the Digital ESS. More on this in the next post.