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Learning Unit 6
Communication Network
 Telecommunication is the transmission of
information over significant distances to
communicate. In earlier times, telecommunications
involved the use of visual signals, such as beacons,
smoke signals, semaphore telegraphs, signal
flags,
A basic telecommunication system consists of three primary
units that are always present in some form:
1) A transmitter that takes information and converts it to
a signal.
2) A transmission medium, also called the "physical channel"
that carries the signal. An example of this is the "free space
channel".
3) A receiver that takes the signal from the channel and
converts it back into usable information.
Communication Codes & Modes
 Data Codes
 Analogue and Digital Transmission
 Asynchronous and Synchronous Transmissions
 Simplex, Half-Duplex and Full-Duplex
Transmission
 Circuit Switching
 Message Switching
 Packet Switching
Data Codes
Data Codes
 Two data code systems are used for communications
namely:
 ASCII (Microsoft uses this 7 or 8-bit system, which is
used by mini and microcomputers to represent data in
binary form).
 EBCDIC (8-bit system used by IBM mainframes to
represent data in binary form).
Communications signals can be either by analog
signals or digital signals. For an analog signal, the signal is
varied continuously with respect to the information. In a
digital signal, the information is encoded as a set of discrete
values (for example, a set of ones and zeros).
Cont..
Characteristics of an analogue
 Continuous;
 Can be a sine wave (not always);
 Transmission distance is high;
 Examples: Human voice and sounds heard by the
human ear. I
Digital Signal
 Short, separate pulses;
 Square waveform;
 Represented using direct current by changing the
voltage;
 Transmission distance is traditionally low.
 Examples: Digital signals are used in computer
systems, CDs and DVDs.
Asynchronous & Synchronous
Asynchronous Transmission:
 The receiver gets the message later than when it was
originally sent (hours or days after the message is
sent).
 Sending a letter through the post office or e-mail over
the Internet are examples of synchronous
transmission.
 Used to reduce transmission time and cost.
 Sends each character separately down a channel.
 Each transmission unit is one character in length.
Synchronous Transmission
Synchronous Transmission:
 Refers to communication in which the receiver gets the
message instantaneously.
 Voice and phone communications are examples of
asynchronous transmission.
 Blocks many characters together for transmission.
 Simplex communication refers to communication
that occurs in one direction only
Half duplex
Full duplex
Circuit switching
 Single and dedicated path between the devices for the
period of the connection.
 Example: Telephone network. It links a sender and
receiver over a dedicated channel, which remains open
until they hang up.
Message Switching
 Does not create a dedicated path between the source
and destination device for the entire dialog.
 If the route from the sender to the receiver is not open,
the message will be stored and forwarded as soon as
the route becomes available.
 Example: Cell phone network
Packet Switching
 Packet switching divides a message into smaller units
called packets containing all source and destination
addresses needed to traverse the network.
 Example: All commercial networks use packet
switching.
telecommunication system consists
A basic
of three primary units that are always present in some form
 A transmitter that takes information and converts it to
a signal.
 A transmission medium, also called the "physical
channel" that carries the signal. An example of this is
the "free space channel".
 A receiver that takes the signal from the channel and
converts it back into usable information.
MEDIA
 Network transmission media - refers to the various
types of media used to carry the signal between
computers
 Wire media (guided)
 Wireless media (unguided)
 Broadband over Power Lines
Wire
Media
 Wire media - transmission material manufactured so
that signals will be confined to a narrow path and will
behave predictably

Three most commonly used types include:
1.
2.
3.
Twisted-pair wiring
Coaxial cable
Fiber optic (or optical fiber)
Wire Media
Wireless Media
 Wireless media - natural parts of the Earth’s
environment that can be used as physical paths to
carry electrical signals
 Atmosphere and outerspace are examples of wireless
media that commonly carry signals
Wireless Media
 Bluetooth
 Infrared transmission
 Zigbee
 Wireless mesh
 3G
 4G
Broadband over Power Lines
 These provide network connections over standard high
voltage power lines.
 To access the Internet, BPL users connect their
computer to a special hardware device that plugs into
any electrical wall socket.
Describe Network Components
1. Hosts (or Servers)/ Client Systems
2. Terminals and Workstations
3. Multiplexers-communications processors, allow
single channel carry data transmission from many
terminals simultaneously
4. Modems –convert digital to analogue
5. Network Hardware devices:
Client/Server
Networks
• Client/Server networks:
use a central computer,
known as a Server to
facilitate communication
and resource sharing
between other computers
on a network, which are
known as Clients.
• In terms of resource
sharing you can compare
the client/server network
to a public library:
Librarians manages the
use of books and other
media by patrons, a
server manages the use
of shared resources by
clients…
Client/Server Networks
 Client/Server network
Advantages of a Client/Server
Network
• Provide User logon accounts and passwords for user of the
network
• Access to multiple shared resources can be centrally granted to a
single user or groups of users
• Problems on the network can be tracked, diagnosed and often
fixed from one location
• Optimized for faster processing time to handle many requests
from clients
• Larger disk space means it is more scalable and more clients
can be added as necessary
Networking Hardware Basics
Hubs
Connectivity device that retransmits
incoming data signals to its multiple
ports –Typically used for Star
topologies and use twisted pair
cabling
Repeaters
A device used to regenerate a signal—
addresses a transmission signal
problem called attenuation
Bridges
Allows large networks to be broken up
into segments-segments are connected
by a bridge----manages bandwidth
Switch
Also manages bandwidth on a large
network—further divides a network
into smaller domains
Router
Routing device that examines each
packet of data it receives and then
Why Use Networks in
Organizations? • Networks allow multiple
• All networks offer
advantages relative to
using a standalone
computer…
• that is, a computer that
is not connected to other
computers and that uses
software applications
and data stored on its
local disks
users to share devices
such as printers, and
share data, for example
spreadsheets which are
collectively known as
network resources.
Advantages
to
using
a
Network
• Sharing devices save
• Sharing devices also saves
money!
• For example, rather than
buying 20 printers for 20
office workers, a company
can have one printer and
have those 20 office
workers share it over a
network.
time!
• For example, its faster for
coworkers to data over a
network than to copy data
to a removable storage
device and physically
transport the storage
device fro one computer to
another.
Sneakernet: an out-dated file-sharing method in which people had
to physically transport data files from one desktop to another,
presumably wearing sneakers!
Why else use networks?
 One of the highest
priority network services
is email!
 Reasons for networks
include;
1.
2.
3.
4.
5.
File & Print services
Remote user access
Mail services
Internet services
Management Services



Most of these listed features
require a NOS, a component of a
Client/Server Network

Traffic monitoring
Load balancing
Security auditing
Backup and restoration
services
Network Concerns (Issues) for
Managers
 Reliability of network hardware and software;
 Response time of network to users accessing the data
and information;
 Cost of hardware and software;
 Compatibility of network with hardware and software;
 Access and security, such as password control and
authentication.
Protocols
 A protocol is a standard
that specifies the format
of data as well as the
rules to be followed
during transmission
 Simply put, for one
computer to talk to
another computer, they
must be speaking the
same language.
 Protocols provide the
langauge
 The
committee
that
IEEE
802.3
or Ethernet
Protocol
addresses LAN standards
is called the IEEE 802
Committee.
 Thus, IEEE LAN
protocols always start
with the number 802.
 Today, the world’s most
popular protocol for
LAN is the IEEE 802.3
protocol.
 This protocol standard, also
called Ethernet, specifies
hardware characteristics
such as which wire carries
which signals.
 It also describes how
messages are to be packaged
and processed for
transmission over the LAN.
TOPOLOGY
• Network topology - refers to the geometric
arrangement of the actual physical organization of the
computers and other network devices) in a network
– Bus
– Star
– Ring
– Hybrid
– Wireless
Bus/Star/Ring Topologies
Bus
Topology
(linear bus)
All devices are connected to a central cable, called
the bus or backbone. These networks are relatively
inexpensive and easy to install for small networks
Star Topology All devices are connected to a central device, called a hub.
Star networks are relatively easy to install & manage, but
bottlenecks can occur because all data must pass through
the hub
Ring
Topology
The ring topology connects computers on a single circle
of cable. Signals travel around the loop in one direction
and pass through each computer acting like a repeater to
boost the signal and send it on to the next computer.
Hybrid / Wireless Topologies
Hybrid Topology
Groups of star-configured
workstations are connected to a
linear bus backbone cable,
combining the characteristics of
bus and star topologies
Wireless
Devices are connected by a
receiver/transmitter to a special
network interface card that
transmits signals between a
computer and a server---all with an
acceptable transmission range
NETWORK TOPOLOGY
NETWORK
TYPES
 The three types of
networks include:
1.
Local area
network (LAN)
2.
Metropolitan
area network
(MAN)
3.
Wide area
network (WAN)
Difference between MANS and
WANS
• MANS: networks that
extend beyond the
boundaries of a building.
• It is a network that is
larger than a LAN and
connects clients and
servers from multiple
buildings
• WANS: a network that
connects two or more
geographically distinct
LANS or MANS.
• Different than MANs
because they typically
transport data over much
longer distances than
MANs and as such often
require different
transmission methods,
media, and use a greater
variety of technologies
LANs, MANs, and WANs Illustrated
Commonly connects
separate offices from the
same organization,
whether they are across
town or across the world
Connecting LANs from
multiple buildings
Within the confines of a room or
single building