TELECOMMUNICATION:A Journey from Manual to Electronic Switching System

Jan 17 • Education, Telecommunication • 7203 Views • 17 Comments on TELECOMMUNICATION:A Journey from Manual to Electronic Switching System

The field of Telecommunication has evolved from a stage when signs and drum beats  were used for long distance communication.In March 1867,Alexander Graham Bell demonstrated his telephone set and laid the foundation of telephony.In actual telecommunication network, subscribers are not directly connected to one another, infact they are connected to switching system.Connection is established between the subscribers at the switching system.The function of switching system is establishing and releasing connection.Earlier,Manual switching systems were used such as Local Battery(LB) or Central Battery(CB).In Local Battery system,Dry cells were used in subscriber sets to power the microphone.In Central Battery system,a subscriber set is energises with a powerful central battery at the exchange.But there were certain limitation of manual switching system,due to which it lost its popularity.

sattelite Telecommunication


click here to join our gate whatsapp group get 50% discount on ebooks of notes at onlinekhanmarket & get 20% discount on studymaterial.oureducation on 1st purchase


  • In a manual exchange,the subscriber needs to communicate with the operator and common language becomes an important factor.
  • Sufficient Privacy is not there as an operator is involved in setting up and monitoring the call.
  • Moreover,the operator takes a few minutes to establish and release of calls.

All these limitations led to the development of Automatic Switching System.Basically,in automatic switching system,Electromechanical (Strowger and Crossbar ) switching system came into existence.Strowger Switching System was developed by ALMON B. STROWGER in 1889.



Strowger switching Systems are constructed using Uniselector or Two motion selector.The wiper contacts of these selectors move in direct response to dialed pulses or signals from the subscriber telephone.The wiper moves forward by one contact at a time and moves by as many contacts as the number of dialed pulses received.

Crossbar switching provides a matrix consisting of  n*m set of contacts and selects one  of the contacts.There is a set of horizontal and vertical bars which are attached to a set of electromagnet. When an electromagnet(in horizontal direction) is energized,the bar attached to it slightly rotates in such a way that the contact points attached to the bar move closer to its facing point but do not make any contact. Now,if an electromagnet in the vertical direction is energized,the corresponding bar rotates and the contact points comes in contact  and a connection is established.

Group Discussion

click here to join our gate telegram group get 50% discount on ebooks of notes at onlinekhanmarket & get 20% discount on studymaterial.oureducation on 1st purchase


  •  In an automatic exchange,the subscriber does not need to communicate with the operator.
  •  A greater degree of privacy is obtained in automatic exchange .
  •  Establishment and Release of calls are faster in automatic exchanges.

Then,in due course of time,Electronic Switching System (Stored Program Control) came into its existence because Electromechanical component’s operational speed is slow and lifetime is limited.

Electronic Switching System is called Stored Program Control because the control of switching functions are programmed into memory and actions are executed by the controlling processor. There are two types of SPC(stored program control):

  •    Centralized SPC
  •    Distributed SPC
Channel fetch

Channel fetch

Centralized SPC: It uses a single processor to perform the exchange function.At present,Centralized SPC uses dual processor for higher reliability.If two processors are used,each must carry the full traffic load if the other fails.Further,Centralizesd SPC is  divided into three sub-modes.These are Standby mode,Synchronous Duplex Mode and Load Sharing Mode.

  • Standby mode: In this mode,only one of the processors will be active and other will be in standby mode.If the active processor fails,then the standby processor takes over the charge.This is further divided into two sub-modes:
  1. Cold standby mode: In this mode,the memory of the standby processor is not updated,so there can be disruption of calls when standby processor takes over the charge.
  2. Hot standby mode:Here,the standby processor is regularly updated with the details of the recent calls,so there will be no disruption of calls when change over takes place.
  • Synchronous Duplex Mode: In this mode,both the processor recieves the same input and operate in synchronism to produce the same result.But the distribution of signals is done by only one processor.The other processor is updated with the details of the recent calls.The result of both the processor is compared by comparator and if any discrepancy is found then the faulty processor is taken out of the service and other processor proceeds with the task
  • Load Sharing Mode: The name itself,signifies that this mode shares the load.Here,instead of comparator,an Exclusion Device is used.Here,both processors works independently and thus at any point of time,they will be performing different tasks for different calls.Exclusion Device ensures that both processors do not process the same call.If one processor fails,then other processor takes over the entire load.

Distributed SPC: In this,there is no central processor for the overall function,instead it involves a number of small  processors (regional processor)to perform the task.But,there is  a central processor to direct the regional processor.Since regional processors take care of the tasks such as line scanning and digit reception,therefore the cental processor is relieved of some work and thus reliability is improved.The function of exchange can be decomposed either horizontally or vertically.
So,two types are there:

  1. Horizontal decomposition: Here,each processor only performs some functions like call processing etc.
  2. Vertical decomposition: Here,all functions of the switching system are divided into smaller processing functions.

Electronic Switching System  can be divided into two parts:

  • Space division switching: In space division switching system,each connection is made over a different path in space.Here,the paths in the circuit are seperated from each other spatially.It was originally designsed for analog network but now it is used both in analog and digital network.
  • Time division switching: Here,each connection is made over the same path in space,but at different instant of time.

Now we have to discuss the Availability of the System.Switching System must be designed to obtain Long Mean Time Between Failure(MTBF).If a system fails,it has to be rectified as soon as possible.If MTBF is longer and Mean Time To Repair(MTTR) is shorter,then the portion of time for which the system provides service is greater.So,basically the” Availability” gives the probability that the system will operate correctly when required.

In this way,we see that how we have advanced in the field of Telecommunication.We started from Manual switching system where we had to suffer from different kinds of problems and now we have come into an era of  Electronic Switching System(Stored Program Control).

Modern telephone exchanges uses STORED PROGRAM CONTROL.It is only due to the use of Electronic Switching System that the call establishment and call release only takes a few seconds. It is only due to these types of advancement in the field of telecommunication,we are able to talk to our well-wishers so easily.

For related topic one can refer to the following:-

  1. Telecommunication
  2. Optical Fiber Communication and optical fiber

Your views are valuable to us. Any type of suggestion will be highly appreciated.

For best ebooks

For best books in hardcopy

Tell us Your Queries, Suggestions and Feedback

Your email address will not be published.

17 Responses to TELECOMMUNICATION:A Journey from Manual to Electronic Switching System

  1. Priyanka Sarkar says:

    Telecommunication is communication at a distance by technological means, particularly means based on electrical signals or

    electromagnetic waves.
    Early communication technologies based on visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and

    optical heliographs are sometimes considered to be forms of telecommunication.Other examples of pre-modern

    “telecommunication” include audio messages such as coded drumbeats, lung-blown horns, and loud whistles. Electrical and

    electromagnetic telecommunication technologies include telegraph, telephone, and teleprinter, radio, microwave transmission, fiber

    optics, communications satellites and the Internet.
    A revolution in wireless telecommunications began in the first decade of the 1900s with pioneering developments in radio

    communications by Nikola Tesla and Guglielmo Marconi. Marconi won the Nobel Prize in Physics in 1909 for his efforts. Other highly

    notable pioneering inventors and developers in the field of electrical and electronic telecommunications include Charles Wheatstone

    and Samuel Morse (telegraph), Alexander Graham Bell (telephone), Edwin Armstrong, and Lee de Forest (radio), as well as John Logie

    Baird and Philo Farnsworth (television).
    The world’s effective capacity to exchange information through two-way telecommunication networks grew from 281 petabytes of

    (optimally compressed) information in 1986, to 471 petabytes in 1993, to 2.2 (optimally compressed) exabytes in 2000, and to 65

    (optimally compressed) exabytes in 2007. This is the informational equivalent of two newspaper pages per person per day in 1986,

    and six entire newspapers per person per day by 2007. Given this growth, telecommunications play an increasingly important role in

    the world economy and the global telecommunications industry was about a $4.7 trillion sector in 2012. The service revenue of the

    global telecommunications industry was estimated to be $1.5 trillion in 2010, corresponding to 2.4% of the world’s gross domestic

    product (GDP).
    Greek hydraulic semaphore systems were used as early as the 4th century BC. The hydraulic semaphores, which worked with water

    filled vessels and visual signals, functioned as optical telegraphs. However, they could only utilize a very limited range of pre-

    determined messages, and as with all such optical telegraphs could only be deployed during good visibility conditions.
    During the Middle Ages, chains of beacons were commonly used on hilltops as a means of relaying a signal. Beacon chains suffered

    the drawback that they could only pass a single bit of information, so the meaning of the message such as “the enemy has been

    sighted” had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain

    relayed a signal from Plymouth to London that signaled the arrival of the Spanish warships.
    Telephone, telegraph,radio,television,video telephony,digital cinema,computer network,internet,satellite systems are the part of the


  2. Sona kumari says:

    A good Article containing the information all about the Telecommunication. I must say it is very much informative. Keep it up.

  3. noopur singh says:


  4. Anamika Tomar says:

    From the discovery of fire then wheel then different complex discoveries in the future,one thing is common in all these discoveries,society and discoveries always grow from simple to complex in structure.Like “the journey of fire is an tremendous example of manual discovery” where our forefathers discovered fire and then they shifted towards more complex discoveries .
    *After the growth of service sector in the same time ,growth of “Telecommunication explored”.If we will see the evolution of Telecommunication,we can find that it has evolved because of importance of long distance communication in a short span of time for which pigeons were used in the past time.The use of pigeons is a kind of manual communication and a use of wireless communication like “mobile phones” is an example of electronic switching system. “And call centers in the present times are kind of “HUBS” also enlightens an another example of successful journey from manual to electronic switching system”.

  5. preeti nisha says:

    Telecommunication is the fastest means of communication and information broadcasting in today’s era.We have seen innumerous advancement in telecommunication since ages. From times when only post cards where the means to communicate to wired telephony systems and now to wireless ones. It is the pioneer key in development of human mankind. Today we live in the age of communication and the advancement has reached to such a stage that it is worth rewarding. Telecommunication is involved in 87% of the tasks what we do today and is just done with transmission of signals. How evolutionary is that! Mobile phones, satellite, internet all have brought people so near and information broadcasting have become so easy today. Very effective piece of information to know how telecommunication evolved.

  6. oishi chatterjee says:

    Telecommunication is the most important way of communication in today’s world. It started from a simple wired telephone. But today every single person has got their personal wireless mobile phone to communicate. It has advanced to such an extent that practically every business implicitly or explicitly depends upon it for their work to be done. Nowadays people even use it to conduct important business meetings overseas . Advent of internet has also been possible because of this telecommunication which is now a necessity for any important and valuable task to be performed. It has progressed as a journey which started from being manual and with its final destination to be infinity as nobody can ever guess where would it end or where would it lead us to but it is for sure that it would never suffer depreciation in any case . Telecommunication is now being carried through electronic switching system (journey continues) which controls the empowerment of progress or development. Ultimately we can just say it is a part of development and is a vital ingredient for further development.

  7. Atif Pall says:

    Telecommunications is a general term for numerous technologies that send information over distances. Mobile phones, land lines,radio and television are all telephony technologies Development in telecommunications have changed the world immeasurably. While pockets of humankind were once isolated from each other, people now have multiple ways to see and hear what is occurring on the other side of the world in real time Satellite technology, television, the Internet and telephony keep the globe connected in a humming buzz of interactive voices and pictures.
    Impressive article to get to know about telecommunications in detail.

  8. shreya sarkar says:

    Graham Bell’s invention has indeed made the world a very small place as people living even in two different continents can communicate with each other by means of a telephone. With further innovation in technology telephone has gone from being manual to automated and much more now. Imagining life without them is kind of impossible. A nice piece of information. Came to know much more besides the already known facts about telecommunication.

  9. Neha S says:

    It was a innovation that changed the world today with his very piece of innovation today we can communicate with any one on the other end of this world.
    But life with manual switching system would have been so difficult, it would have been like every time there is someone keeping a watch on you..
    Life would have been difficult at that time, as i love the present system of automatic switching system and life is so much easier now, Thanks to the person who brought about this change..

  10. sibanjan says:

    telecommunication system has so much importance n modern human civilization … from 1867 the system has gone through different stages and under different development….the world’s effective capacity to exchange information through two-way telecommunication networks grew from 281 petabytes of information in 1986, to 471 petabytes in 1993, to 2.2 exabytes in 2000, and to 65 exabytes in 2007…. with the increase of the user… certain developments were needed… presently satellite is used as a medium of communication….

  11. Saheli Dasgupta says:

    An awesome piece of information. All engineers irrespective of their streams should go through this. you all would definitely gain quite a lot of much needed basic knowledge about the most widely used technology which is almost indispensable in today’s world. And even the non-technical people should go through this and enrich their knowledge. I myself found it quite useful & hope everyone going through this article would also be able to say the same.

  12. sumit mukherjee says:

    Telecom is the backbone of communication. Starting from POT’s to PSTN and from 2g to 5g all are the gift of telecommunication. Now as the number of user increases, the investmenters feel the need of more advanced telecom medium. So, the scientists finally found the way out from it by using electronic switching. And we all know that how it takes the place of the manual phone.

  13. SHRUTI PRIYA says:

    COMMUNICATION ENGINEER- GO through this article to know about a part of telecommunication…. Switching Theory,SPC and its types.

  14. aratrika sengupta says:

    Telecommunication in the modern era is the science and practice of transmitting and receiving information by electromagnetic means. So I guess the dice has changed and evolution from manual operation to just few buttons exhibits another arena of technology. The article was really helpful.

  15. kinsuk sadhukhan says:

    Really interesting article about telecommunication.Good writing and got some more knowledge about electronic switching system.keep it up.

  16. sukanta bakuli says:

    good article on telecommunication.i must say good style of blogging too. keep it up.

  17. AJIT PRAKASH says:

    this was a very informative article. got many doubts regarding the subject cleared. Information was given in a simple language and i liked it.

« »