What is understood by the term Communication?

The term communication is defined as the act of disseminating information. It presupposes that:

there is information to disseminate
the desire to disseminate exists
there is an agency to send/transmit information
there is a means of encoding information
there is a medium to carry the information
there is a recipient to receive the information
the recipient is capable of understanding the information received


Data Transfer Requirements (1)

Consider the internal work of The Little Man Computer when data is to be transferred from the calculator to a memory location (for example location 99). This transfer will require:

identifying the destination, i.e. getting its address (in this case 99)

advising it that data will be written into it

preparing the internal bus structure for data transfer

instructing the calculator when and how to send its data.


Data Transfer Requirements (2)

From this example, you will have noted that transferral of data requires:

a sender to send the message, in this case the calculator
addressing to identify the destination, in this case memory address 99
a transmission medium to allow data flow, in this case the Little Man Computer’s internal bus
a receiver to receive the message - the memory location addressed as 99
co-operation between sender and receiver.
to be error free
is compatible with the transmission medium
is in a format which can be used by the receiver
has been successfully received


Basic Elements of a Communication System

From the above discussion, in any communication between two entities we can
identify the following basic elements:

1. Sender
2. Receiver
3. Addressing - identifies where the Receiver is
4. Protocol - set of co-operation rules to achieve communication
5. Transmission code - “language” being used
6. Transmission rate - speed at which “what is being communicated” is being sent
7. Transmission synchronisation - how to recognise what is being communicated
8. Transmission medium
9. Error detection and correction
10. Transmission efficiency - how much of what is being sent is useful to the receiver


Data Transmission Fundamentals - Some Terminology

Data transmission between sender and receiver occurs over some transmission medium.
Transmission may be simplex, half-duplex, or full-duplex
Transmission media may be classified as guided or unguided. In both cases communications is in the form of electromagnetic waves.
The term direct link, also known as data link, is used to refer to a transmission path in which signals propagate directly from transmitter (sender) to receiver with no intermediate devices, other than amplifiers or repeaters used to increase signal strength.
A guided transmission medium is point-to-point if it provides a direct link between two devices, and those are the only two devices sharing the medium.
In a multipoint guided configuration, more than two devices share the same medium.


Signalling Technologies

Baseband is the transmission of digital signals without modulation. In a baseband communication network, digital signals (0s and 1s) are put onto the medium as voltage pulses. The entire bandwidth is consumed by the signal.
Broadband uses coaxial cable to provide data transfer by means of analogue signals. The bandwidth is divided in different frequency bands or channels. In a broadband communication network involving computers, digital signals are passed onto the medium through a modem and transmitted over one of the channels. So, several different communication networks can be implemented over the same medium.
Analogue transmission is used to mean the transmission of analogue signals without regard to their content.
Digital transmission, on the other hand, is used to mean the content of the signal.