Evolution of Switching in Telephony and Networks
Manual switching system in Telephony and NetworksIn the infancy of telephony, telephone exchanges were built up with manually operated switching equipment. The first manual exchange was installed in New Haven, USA, in 1878. The operators received calls and switched them manually to the called subscriber. When the call was complete, the operator released the connection. We might say that the operator was the "control system" of that era.
Electromechanical switching systemsAlmon B. Strowger, Kansas City, USA, is regarded as the father of automatic switching. Although these systems required more maintenance, their overall impact was positive since the number of operators could be reduced significantly. The systems provided increased traffic capacity at a lower cost, preparing the way for a continued rapid expansion of the telecommunications network. The new systems also made it possible to route traffic more efficiently through the transmission network, reducing the need for cable capacity.
Digital, computer-controlled switching systemsA technique for saving expensive connections was introduced into the long-distance networks: frequency division multiplexing (FDM). It was implemented in 1950 when about 1,000 channels were transferred on the same cable (the coaxial cable).
Digital multiplexing (based on PCM), introduced around 1970, also made transmission networks less expensive while at the same time improving transmission quality. Costs were further reduced when digital group switches were combined with digital transmission systems, eliminating the need for many relatively expensive analog-digital (A/D) converters. It now became necessary to computerize the control of the exchanges, and before long, not only the group switches but the entire exchanges were digital. The first computer-controlled exchange was put into service in 1960 in the US and in 1968 in Europe.
Special nodes for data communicationStrong growth in data traffic has resulted in the development of separate data networks and data switches. Packet mode and frame relay, for example, provide efficient network utilization, enable packets to be retransmitted when errors occur on a link, and allow for sorting, routing, and buffering.
Nodes for N-ISDN and B-ISDNDevelopments for providing service-integrated networks for voice, video, and data services require both public and private Narrowband-ISDN. In principle, a complete ISDN node can be seen as a combination of today's telephone exchanges and packet data switches (circuit switching and packet mode), with an important sorting function for subscriber traffic.
The ATM technology applies the cell-switching technique and which forms the basis of Broadband-ISDN, is not yet completely standardized.
Optical switchesIt is primarily the switching equipment that limits the bandwidth of a connection. Today, we can make use of very high bit rates, up to tens of billions of bits per second in optical transmission systems. However, in switching equipment, we must change over to electrical signals and considerably lower bit rates.
The next step is to use optical switching with electronic switch control. And in time, we will most assuredly have fully optical switching systems.
Evolution of Switching in Telephony and Networks Reviewed by Adnan Malik on 1:31 AM Rating: