CHAPTER 1
Communication Systems
Concepts
352 ‫شال‬
Banan Mahmoudi
Introduction
By the end of this course, we should be able to:
– Understand basics of communication systems
– Understand basics of communication channels
– Understand types of data and signals
– Differentiate among the basics of some
communication techniques
– Apply some communication techniques in solving
simple problems
Introduction
• Telecommunication is the transmission of
information, over significant distances, for the
purpose of communication.
Introduction
• In earlier times, telecommunications involved the use of
visual signals, such as beacons, smoke, semaphore
telegraphs, signal flags, and optical heliographs, or audio
messages via coded drumbeats, lung-blown horns, or sent by
loud whistles, for example.
• In the modern age of electricity and electronics.
Telecommunications now also includes the use of electrical
devices such as telegraphs, telephones, and teletypes, the
use of radio and microwave communications, as well as fiber
optics and their associated electronics, plus the use of the
orbiting satellites and the Internet.
1. BASIC TELECOMMUNICATION SYSTEM
• The fundamental purpose of a communication system is
the exchange of data between two parties. A very simple
telecom system is shown in Figure 1.
1. BASIC TELECOMMUNICATION SYSTEM
• At the transmitting end, there will be a source
that generates the data.
• and a transducer that converts the data into
an electrical signal.
• The signal is sent over a transmission medium.
• At the receiving end, the transducer again
converts the electrical signal into data and is
given to the destination .
1. BASIC TELECOMMUNICATION SYSTEM
• For example, if two people want to talk to each other
using this system, the transducer is the microphone
that converts the sound waves into equivalent
electrical signals. At the receiving end, the speakers
convert the electrical signal into acoustic waves.
Similarly, if video is to be transmitted, the
transducers required are a video camera at the
transmitting side and a monitor at the receiving side.
The medium can be copper wire.
2. TYPES OF COMMUNICATION
• Based on the requirements, the communications can
be of different types:
I.
Point-to-point communication: In this type,
communication takes place between two end points. For
instance, in the case of voice communication using
telephones, there is one calling party and one called
party. Hence the communication is point-to-point.
II. Point-to-multipoint communication: In this type of
communication, there is one sender and multiple
recipients. For example, in voice conferencing, one person
will be talking but many others can listen.
2. TYPES OF COMMUNICATION
III. Broadcasting: In a broadcasting system, there is a central
location from which information is sent to many
recipients, as in the case of audio or video broadcasting.
In a broadcasting system, the listeners are passive, and
there is no reverse communication path.
IV. Simplex communication: In simplex communication,
communication is possible only in one direction. There is
one sender and one receiver; the sender and receiver
cannot change roles.
2. TYPES OF COMMUNICATION
V. Half-duplex communication: Half-duplex communication
is possible in both directions between two entities
(computers or persons), but one at a time. A walkie-talkie
uses this approach. The person who wants to talk presses
a talk button on his handset to start talking, and the other
person's handset will be in receive mode. When the
sender finishes, he terminates it with an over message.
The other person can press the talk button and start
talking. These types of systems require limited channel
bandwidth, so they are low cost systems.
2. TYPES OF COMMUNICATION
VI. Full-duplex communication: In a full-duplex
communication system, the two parties—the caller and
the called—can communicate simultaneously, as in a
telephone system.
However, note that the communication system allows
simultaneous transmission of data, but when two persons
talk simultaneously, there is no effective communication!
The ability of the communication system to transport
data in both directions defines the system as full-duplex.
3. A Communications Model
• We begin our study with a simple model of communications,
illustrated by the block diagram in Figure l.la.
A Communications Model
• The key elements of the model are :
1. Source. This device generates the data to be
transmitted; examples are telephones and personal
computers.
2. Transmitter - Transforms and encodes the information to
produce electromagnetic signals that can be transmitted
across transmission medium.
A Communications Model
3. Transmission system :
- transmission line
- Complex network
4. Receiver : accepts the signals from the transmitter
system and converts it into a form that can be handled
by the destination device.
5. Destination. Takes the incoming data from the receiver.
Communications Tasks
Transmission system utilization Addressing
Interfacing
Routing
Signal generation
Recovery
Synchronization
Message formatting
Exchange management
Security
Error detection and correction
Network management
Flow control
4. DATA COMMUNICATIONS
• The following is a simplified data communications model.
• Suppose that the input device and transmitter are
components of a personal computer.
• The user of the PC wishes to send a message m to another
user.
• The user activates the electronic mail package on the PC
and enters the message via the keyboard (input device).
• The character string is buffered in main memory (bit
stream).
• The PC is connected to some transmission medium, such as
local network or a telephone line, by an I/O device
(transmitter) such as modem.
• The input data are transferred to the transmitter as a
sequence of voltage shifts.
4. DATA COMMUNICATIONS
• The transmitter is connected directly to the medium and
converts the incoming stream into a signal suitable for
transmission.
• The transmitted signal is subject to some impairment before
it reaches the receiver. Thus, the received signal may differ
from the transmitted signal.
• The receiver will attempt to estimate the original signal,
based on the received signal and its knowledge of the
medium, producing a sequence of bits.
• These bits are sent to the output personal computer, where
they are buffered in memory.
• In many cases, the destination system will attempt to
determine if an error has occurred and, if so, try to correct it.
• The data are then presented to the user on screen or printer.
TRANSMISSION OF INFORMATION:
• The basic building block of any communications
system facility is the transmission line.
• The transmission line must have the required
capacity, acceptable reliability and minimum cost.
TRANSMISSION OF INFORMATION:
• The most commonly used transmission media are:
 Twisted-pair lines,
 Coaxial cables,
 Optical fiber cables,
 Satellite microwave.
TRANSMISSION OF INFORMATION:
• The data rates that can be achieved and the rate at
which errors can occur depend on:
 The nature of the signal
 Type of the medium.
Communication techniques:
 Inserting a signal on the medium
 Encode the information into an electromagnetic
signal
 Interface between a device and the transmission
medium
 Controlling the flow of information
 Recovering information from its loss or corruption
TRANSMISSION EFFICIENCY:
• The cost is a very important factor in any
communication system. The amount of information
that can be carrier over a given resource must be
maximized by two ways:
 Multiplexing
 Compression
NETWORKS
• A computer network, often simply referred to as a network,
is a collection of computers and devices interconnected by
communications channels that facilitate communications
among users and allows users to share resources.
• Networks are often classified as
 local area network (LAN)
 wide area network (WAN).
NETWORKS
• A local area network (LAN) is a computer network that
connects computers and devices in a limited geographical
area such as home, school, computer laboratory or office
building. The defining characteristics of LANs, in contrast to
wide area networks (WANs), include their usually higher
data-transfer rates, smaller geographic area, and lack of a
need for leased line.
NETWORKS
• A wide area network (WAN) is a computer network that
covers a broad area. WANs are used to connect LANs and
other types of networks together, so that users and
computers in one location can communicate with users and
computers in other locations. Many WANs are built for one
particular organization and are private. Others, built by
Internet service providers, provide connections from an
organization's LAN to the Internet.