Today the smart phone acts as a five inch any-time any-where television. The smartphone should be either renamed as 'microTV' or 'personalTV' or else we have to accept it is an irony (using a phone to see video). The name smartphone suggests that 'it is an intelligent phone'. We can infer the 'device' was not developed to see video. But it acquired the capability to display video.
Working of telephone or any other artifacts of technology are explained in books or magazines through technological point of view. If we are not able to grasp the technology, then we are unable to understand the working of the device. Technical systems are explained with use of mathematics. Invariably common man's grasp on mathematics is poor and in turn makes shallow understanding. Next, technology-centered explanation uses lot of technical words. This makes English as the best medium to convey concepts. Thus a "glass ceiling" is created for common man who lives in Asia or Africa. As the technologies are changing rapidly and technology centered pedagogical approach is really outdated.
We can safely presume any technological device is produced to carry out function(s). This leads us to write a pseudo-mathematical equation
Working of telephone or any other artifacts of technology are explained in books or magazines through technological point of view. If we are not able to grasp the technology, then we are unable to understand the working of the device. Technical systems are explained with use of mathematics. Invariably common man's grasp on mathematics is poor and in turn makes shallow understanding. Next, technology-centered explanation uses lot of technical words. This makes English as the best medium to convey concepts. Thus a "glass ceiling" is created for common man who lives in Asia or Africa. As the technologies are changing rapidly and technology centered pedagogical approach is really outdated.
We can safely presume any technological device is produced to carry out function(s). This leads us to write a pseudo-mathematical equation
Device = Function + Technology ... (1)
For example, the terms like gel pen, fountain pen and ball-point pen emphasize the type of ink and nibs used in the pen. It is not necessary to know the type of ink or nib to understand the function of a pen. Term like 'Writing Instrument' if used in place of gel pen then the underlying technology is subdued and the function of the pen is emphasized. This delinking makes learning easier for common man and creates the curiousity to understand the technology. This function-centred approach will be used in series of posts to explain smartphone.
In a function-centred approach telephone is seen as a range (distance) extender of voice conversation compared to face-to-face conversation. When human being speaks acoustic waves (pressure waves or sound signals) are generated through mouth and at the time of hearing sound signals are converted into stimuli to brain through ears. The acoustic waves that travel through air are actually radiated and loose energy very quickly. If the acoustic waves are made to travel through the medium then they can travel farther. Based on this principle tin can phone was made. The phone consists of two diaphragms with a taut string or wire, which transmits sound by mechanical vibration from one to the other along the wire [1]. Bottoms of paper cups or metal cans can be used as diaphragms. The phone has a maximum range of 800 meters.
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| Figure 1. Tin-can phone is used by two ladies |
Scientists understood electrical signals travel farther distance than the sound signals. Thus generated sound signals are converted to electrical signals using microphone and sound signals are regenerated by loud speakers. Both microphone and loud speaker are classified as transducers. We can hear as well as talk simultaneously. Only at the time of heated arguments or word duels we do hearing and talking. In normal occasions we take turns to speak or hear. Thus if two people want to talk over long distance then both of them should have microphone and loudspeaker. A long copper cable is required to connect the transducers. To understand connection implementation, knowledge of electrical sciences is must. So, we will conveniently skip it.
If we develop a pseudo-mathematical equation for telephone system, it will result as
Telephone system = Telephone (Bob) +Cable+Telephone (Allen) ... (2)
where Bob and Allen are names of two users. The equation (2) represents the minimum workable telephone system. It shown in Figure 2(a).
If we assume Bob is having is telephone in is hall then whatever conversation that goes on can be heard by Allen. So, to maintain privacy microphone should be disconnected when not in use. The pseudo equation for telephone is given as follows
Telephone =Transducer (Loudspeaker) + Transducer (microphone) with switch ... (3)
Direct method
If Joe (a third person) wants to join with Bob and Allen then dedicated cables are laid to Bob’s and Allen’s houses from Joe's premises. Thus each of them will have two cables in their respective houses. If 20 people are in the group then each house will have 20 cables. Twenty cables have to be brought to each house by overhead wiring. In overhead wiring each cable should be separated by a minimum distance from other cable to avoid cross talk. So, having hundreds of user using this method seems impossible. Next, whenever a user joins the group or leaves the group then a line or cable has to be removed from every user’s house as well as from overhead post. This seems quite tedious. This dedicated line arrangement can be analyzed using 'Graph Theory' (a field in mathematics). Here each telephone is considered as a node (represented as a circle in Figure 2(b) and 2(c)) and each cable is treated as a link. This arrangement is called 'fully connected' system. In this if n nodes are there it requires n(n-1)/2 links are required [2]. It means for just 100 users 4950 links are required.
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| Figure 2. (a) A simple telephone system (b) Fully connected system (c) Local exchange (Bob and Mathew) and central exchange (Brown circle) |
Call office method
Let us make Bob as the administrator of the group and expect everyone to be connected to his house only. Assume he is dedicated and ready to work for 24x7. If Bob wants to call Joe then he will connect the microphone to telephone and instruct Allen to connect to Joe. Allen has to take a piece of wire (patched chord) and connect Bob’s cable and Joe’s cable. After the end of the conversation the patched chord is unplugged. This configuration is called 'star topology'.
The merits of these systems are
If Bob starts collecting fee for the service he offer and employ female(s) then his house can be construed as a Call Office or Telephone Exchange. Likewise nearby Mathew is also offering the same service like Bob. Now, Joe wants to connect to Lucy who is in Mathew's group. To make a connection between Joe and Lucy beforehand Bob and Mathew should be connected in a star topology. After joining in a network Bob’s and Mathew’s Call Offices (CO) are called Local Exchange and the office in which local exchanges are connected is called Central Exchange. The level of connections extended between city to city, province to province and nation to nation. The present method employing female operators to connect lines are called Manual exchange.
In the next post we will discuss the limitations of manual exchange and the evolution of automatic exchange. Early systems used analog electrical signals only later digital electrical systems introduced. The reasons will also be discussed.
Let us make Bob as the administrator of the group and expect everyone to be connected to his house only. Assume he is dedicated and ready to work for 24x7. If Bob wants to call Joe then he will connect the microphone to telephone and instruct Allen to connect to Joe. Allen has to take a piece of wire (patched chord) and connect Bob’s cable and Joe’s cable. After the end of the conversation the patched chord is unplugged. This configuration is called 'star topology'.
The merits of these systems are
- Number of lines present in each house is one irrespective of the number of users (technical term subscribers) in the group.
- If a new member added then only one wire has to be added to Bob's house.
- If n nodes are there then we need only n links
- As only one line is there per house, overhead wiring becomes simpler.
If Bob starts collecting fee for the service he offer and employ female(s) then his house can be construed as a Call Office or Telephone Exchange. Likewise nearby Mathew is also offering the same service like Bob. Now, Joe wants to connect to Lucy who is in Mathew's group. To make a connection between Joe and Lucy beforehand Bob and Mathew should be connected in a star topology. After joining in a network Bob’s and Mathew’s Call Offices (CO) are called Local Exchange and the office in which local exchanges are connected is called Central Exchange. The level of connections extended between city to city, province to province and nation to nation. The present method employing female operators to connect lines are called Manual exchange.
In the next post we will discuss the limitations of manual exchange and the evolution of automatic exchange. Early systems used analog electrical signals only later digital electrical systems introduced. The reasons will also be discussed.
References
[1] History of the telephone - Wikipedia, the free encyclopedia, https://en.wikipedia.org/wiki/History_of_the_telephone
[2] J. J. O Reilly, Telecommunication Principles, Springer Science & Business Media, 2012,
