CSCD 218 : DATA COMMUNICATIONS
AND NETWORKING 1
LECTURE 2
INTRODUCTION AND BASIC CONCEPTS
NETWORK TYPES, NETWORK COMPONENTS/DEVICES
NETWORKING IMPORTANCE AND THE INTERNET
LECTURER : FERDINAND KATSRIKU (PhD)
Computer Network – Some
Terminologies
Computer Network : A collection of computing
devices connected in order to communicate and
share resources.
Connections between computing devices can be physical
using wires or cables or wireless using radio waves or
infrared signals.
Host (Node): Any device on a network
Data Transfer Rate (Bandwidth):The speed with
which data is moved from one place to another on
a network.
Internet Service Provider (ISP): A company that
provides other companies or individuals with access
to the Internet.
Some Terminologies (Cont.)
Protocol : A set of rules that defines how data is
formatted and processed on a network; i.e., rules that
allow client/server interaction.
File Server : A computer that stores and manages files
for multiple users on a network.
Web Server : A computer dedicated to responding to
requests (from the browser client) for web pages.
Internet Backbone : A set of high-speed networks
that carry Internet traffic, provided by companies
such as AT&T, Verizon, GTE, British Telecom, and IBM
Types of Networks
Several different types of computer networks.
Can be characterized by their size as well as their
purpose.
Size can be expressed by the geographic area they
occupy and the number of computers that are part
of the network.
Networks can cover anything from a handful of
devices within a single room to millions of devices
spread across the entire globe.
Types of Networks
The main types are :
i)Local Area Network ii)Metropolitan Area Network
iii)Wide Area Network iv)Personal Area Network
v)Campus Area Network
Some types of networks serve a very particular
purpose. Such include :Storage Area Network,
Enterprise Private Network and Virtual Private
Network.
Local Area Network (LAN)
A network that connects a relatively small number
of machines in a relatively close geographical area.
Traditionally were all cabled but now often use
wireless technology.
Distances between buildings dictate the type of
communication media used (fibre optic, radio links).
Wireless LAN uses radio waves, satellite, microwave
to transmit signals between nodes.
A local area network may serve as few as two or
three users or as many as thousands of users.
Local Area Network (LAN)
Local Area Network (LAN)
Advantages :
1.
2.
3.
Cost reductions through sharing of information and databases,
resources and network services.
Increased information exchange between different departments in
an organization, or between individuals.
The trend to automate communication and manufacturing process
Disadvantages :
1.
2.
3.
Special security measures are needed to stop users from using
programs and data that they should not have access to.
Networks are difficult to set up and need to be maintained by
skilled technicians.
If the file server develops a serious fault, all the users are affected,
rather than just one user in the case of a stand-alone machine.
Metropolitan Area Network (MAN)
A Metropolitan Area Network (MAN) is a network
that is utilized across multiple buildings
Commonly used in school campuses or large
companies with multiple buildings
Is larger than a LAN, but smaller than a WAN
Is also used to mean the interconnection of several
LANs by bridging them together. This sort of
network is also referred to as a campus network
Metropolitan Area Network (MAN)
Metropolitan Area Network (MAN)
Advantages :
 It provides a good back bone for a large network and provides greater
access to WANs.
 The dual bus used in MAN helps the transmission of data in both direction
simultaneously.
 A Man usually encompasses several blocks of a city or an entire city.
Disadvantages :
 More cable required for a MAN connection from one place to
another.
 It is difficult to make the system secure from hackers and industrial
espionage (spying) graphical regions.
Wide Area Network (WAN)
The WAN is a communications network that makes
use of existing technology to connect local
computer networks into a larger working network
that may cover both national and international
locations.
WAN provides long distance transmission of data,
voice, image and video information over large
geographical areas that may comprise a country, a
continent.
Range: Beyond 100 km.
Eg: The internet
Wide Area Network (WAN)
Wide Area Network (WAN)
Wide Area Network (WAN)
Wide Area Network (WAN)
Advantages :
1.
2.
3.
4.
5.
Covers a large geographical area so
long distance businesses can
connect on the one network.
Shares software and resources with
connecting workstations.
Messages can be sent very quickly
to anyone else on the network.
These messages can have pictures,
sounds, or data included with them
(called attachments).
Expensive things (such as printers
or phone lines to the internet) can
be shared by all the computers on
the network without having to buy
a different peripheral for each
computer.
Everyone on the network can use
the same data. This avoids
problems where some users may
have older information than others.
Disadvantages :
1. Need a good firewall to restrict
outsiders from entering and
disrupting the network
2. Setting up a network can be an
expensive, slow and
complicated. The bigger the
network the more expensive it
is.
3. Once set up, maintaining a
network is a full-time job which
requires network supervisors
and technicians to be employed.
4. Security is a real issue when
many different people have the
ability to use information from
other computers. Protection
against hackers and viruses adds
more complexity and expense.
Personal Area Network (PAN)
A computer network organized around an individual
person within a single building . This could be inside
a small office or residence.
A typical PAN would include one or more
computers, telephones , peripheral devices , video
game consoles and other personal entertainment
devices.
If multiple individuals use the same network within
a residence, the network is sometimes referred to
as home area network, or HAN.
TYPES OF NETWORK - BY ARCHITECTURE
Architecture : design of a computer network; way in
which they are connected.
Client / Server – one machine (the server) serves out
data or files to a number of other machines (clients)
Peer to Peer – all devices are at the same level, no
server.
Internet Peer to Peer – allows users to connect to
someone else’s computer over the internet.
TYPES OF NETWORK - BY ARCHITECTURE
Client/Server :
• One computer program (the ‘client’) asks another
computer program (the ‘server’) to provide a service,
such as looking up and providing data, delivering email,
sending web pages, bank balances etc.
• The server is a larger, faster more expensive computer
that is designed to handle a number of tasks at once.
All server software is multi-tasking; (able to process
instructions from more than 1 program at the same
time).
• Some different types of servers:
•
file servers, store files for use on client computers
• application servers, store applications to enable clients access
Client/Server : types of servers
Print servers, accepts print jobs over the network faster than a printer;
workstation gets on with other tasks whilst printing is done
Database server; hold d/bases and allows them to be used by many
users
Web servers, connected to internet and serve webpages to viewers
Domain name servers, (DNS’s); translate domain names into IP addresses;
browsers request the DNS to provide the IP address so that it can
locate website or mail server.
Dynamic host configuration protocol server, (DHCP), hand out the node
number to each device
Peer-to-Peer networks
Each computer on network shares its hardware and
software with all other computers on the network.
No server, so costs are low and installation is simple
All computers and users have equal authority and
rights
Little protection of one workstation against another
Used at home or in small organisations with trusted
users
Allows sharing of files, internet connection, printer
Intranets
 An internal secured environment that has a similar
look and feel of the internet, but operates as a LAN
(ie: within one organisation).
Benefits include:
• access to info is controlled
• improves communication within an organisation
• reduces costs as requires less paper documents
• documents are easier to find and access
• less document maintenance is required.
NETWORK COMPONENTS / DEVICES
Several components make up a network. Such components include :
• hosts (PCs, laptops, handhelds)
• bridges
• routers & switches (IP router, Ethernet switch)
• links (wired, wireless)
• gateways
• repeaters
• hubs
Hubs
A hub interconnects two or more workstations into a local
area network.
When a workstation transmits to a hub, the hub immediately
resends the data frame to all connecting links.
A hub is the central meeting point where cables join to carry
information to other resources through a network.
Hubs have a simple design and they rarely wear out.
Hubs
Hubs
Hubs – How hubs work
Switches
 Switches, like hubs, provide a centralized connection.
 Rather than forwarding data to all the connected ports, a
switch forwards data only to the port on which the
destination system is connected.
 It looks at the Media Access Control (MAC) addresses of the
devices connected to it to determine the correct port.
 Switches learn certain information about the data packets
that they receive from computers on the network.
 They use this to build forwarding tables to determine the
destination of data being sent by one computer to another
on the network.
 They help segment a network and reduce network traffic
congestion by limiting each port to its own collision domain
Switches
Switches – How switches work
Bridges
 Bridges operate at the data link layer of the OSI model.
 The function of the bridge is to make intelligent decisions
about whether or not to pass signals on to the next
segment of a network.
 When a bridge sees a frame on the network, it looks at the
destination MAC address and compares it to the forwarding
table to determine whether to filter, flood, or copy the
frame onto another segment.
 The basic function of a bridge is to join two or more
separate networks that use the same networking language,
called protocol.
Bridges
Routers
 Routers operate at the Network layer of the OSI model.
 They are slower than bridges and switches but make
"smart" decisions on how to route packets received on one
port to a network on another port.
 Routers are capable of segmenting the network.
 Routers are network devices that literally route data around
the network.
 They depend on IP addresses to determine the destination
of packets than MAC addresses of various connected
stations.
 Connects 2 or more networks and uses network layer
addresses (like IP address) to make data forwarding
decisions.
Routers
Repeaters
 A repeater receives the signal, regenerates it, and passes it
on.
 Repeaters are used mainly at the edges of networks to
extend the wire so more workstations can be added.
 Repeaters clean, amplify, and resend signals that are
weakened by long cable length.
 Built-in to hubs or switches.
 Allows extension of a network beyond physical length
limitations
Repeaters
Gateways
 Connects 2 or more networks that can be of different types
and provides protocol conversion so that end devices with
dissimilar protocol architectures can interoperate.
Gateways
137.22.144.6
Netware
Gateway
TCP/IP
145.65.23.102
Advantages of Computer Networks
File sharing
Resource sharing
Communication and collaboration
Remote access
Data protection
THE INTERNET
THE INTERNET
SHORT VIDEO ON INTERNET HISTORY