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:
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.
- a process for information to pass between a sender and receivers
- transfer of meaningful information
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
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.
A brief history of electronic telecommunications begins on page 35. You
should be aware of the some of the major players:
- 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
- Ergonomics - This relates to the study of motion at work, and
means that a system should not cause undue stress or fatigue to use
- Flexibility - This means that the system should be easy to
change, improve and upgrade.
And some major events:
- 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
- The Bell System
- 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