CIS 361 Data Communications and Networks

Chapter 1: Introduction to Telecommunications



This chapter introduces basic telecommunications concepts. The objectives important to this chapter are:

  • defining communications and telecommunications
  • define the basis elements in telecommunications
The concept of communications is quite broad. It includes oral communication, body language, written communications, broadcast communications and network communications.

On page 4, your book offers several definitions of communications:

  • a process for information to pass between a sender and receivers
  • transfer of meaningful information
It is important to note that communication does not take place unless the messages passed are understood. This is the relevance of the author's note about the tree falling in the forest. He is incorrect, in that he says no sound is made if no one hears. Sound is a physical phenomenon resulting from the vibration of air molecules. He is, however, correct that communication does not take place unless the receiver of the message understands it.

On page 7, there are some examples of telecommunications using a standard model. A signal is generated by a source, flows across a medium, and is received by a sink. This is a basic idea from thermodynamic physics, illustrated by heat flowing from a hot source to a cold sink by way of some connecting medium.

Another set of terms that addresses communications more directly says that the signal is originated by a transmitter, flows through a medium and is picked up by a receiver. This happens with a telephone each time you use it. The phone on each end serves as both transmitter and receiver, while the wire network in between serves as the medium. In the case of a cell phone, the medium is simply the radiant energy of the cell phone (it is really a radio) that is received by the closest cell tower and passed into the telephone wire network.

Communications in general, and telecommunications in particular, must have rules (called protocols) to take place. For instance, no communication is possible if the transmitter is sending in a language the receiver does not understand.

The author spends several pages describing how telecommunications are used at home and at work by many people. This web page is an example of telecommunications, involving writing, software and electronic means. In describing some on the components involved in this type of exchange, the author gently points out to us that there are more components involved than the casual observer may think.

On page 24, the author lists several requirement that customers place on a telephone system. These requirements are revised once for people with special requirements (e.g. needing sound amplification) and again for heavy users such as business offices.

These same requirements are applied to data communications systems on page 25, and discussed in greater detail.

  • Availability - Where the phone system is meant to connect to others worldwide, it is assumed to be available 24 hours a day, 7 days a week. A data communications system may not have such an unforgiving requirement, if the enterprise using it is not worldwide or is not open all hours, every day.
  • Reliability - We must understand some mathematical realities about reliability. Each component of a system will have some reliability rating less than 100%, since it will eventually fail. Components connected in series depend on each other for a system to work. To calculate the reliability of such a system, you multiply the reliability factors for the components together. For example if component A is .90 reliable, component B is .95 reliable and component C is .99 reliable, the reliability rating for the three components together is .84645. (Don't trust me, do the math!) recommendation is to design redundancy into the system so if a component fails the system still works.
  • Online and Realtime - Online means that something is available to the system. Realtime means that it reacts fast enough to make the reaction time unnoticeable. Real enough time means that the reaction time of the system may be noticeable, but it is acceptable.
  • Responsive - This is a measure of how long we wait for the system to do what we ask. Different tasks and different systems have different values. A concept related to this is think time, the time it takes a user to interpret the response and take the next action.
  • Ease of Use - Two concepts are presented: Easy to Learn, which means that a user needs little training to use it, and Easy to Use, which means that a user may do almost anything with the system
  • Ergonomics - This relates to the study of motion at work, and means that a system should not cause undue stress or fatigue to use it.
  • Flexibility - This means that the system should be easy to change, improve and upgrade.
A brief history of electronic telecommunications begins on page 35. You should be aware of the some of the major players:
  • Samuel F. B. Morse, who invented the telegraph and Morse code
  • Alexander Graham Bell, who received the American patent for the telephone
  • Western Union, the telegraph company that turned down buying the telephone patents
  • The Bell System
And some major events:
  • The invention of the telegraph
  • The creation of telegraph networks
  • The invention of the telephone
  • The creation of telephone networks
  • The invention of vacuum tubes
  • The invention of transistors
  • The invention of computers
  • The legal approval to add external equipment to phone equipment