Notes of Introduction to Computer Networks.ppt

Lectures about Networks

1. INTRODUCTION TO COMPUTER
NETWORKS

2. A network is a group of interconnected
two or more computers that are linked in
order to share resources such as
printers , exchange files, or allow
electronic communications.
The computers on a network may be
linked through cables, telephone lines,
radio waves, satellites, or infrared light
beams.

4. Resource Sharing
Hardware (computing resources, disks, printers)
Software (application software)
Information Sharing
Easy accessibility from anywhere (files, databases)
Search Capability (WWW)
Communication
Email
Message broadcast
Remote computing
Distributed processing (GRID Computing)

5. Speed.
Networks provide a very rapid method for sharing and
transferring files.
Resource Sharing.
Sharing resources is another area in which a network
exceeds stand-alone computers. Most organizations
cannot afford enough laser printers, fax machines,
modems, scanners for each computer.

6. Ease of communication
E-mail aids in personal and professional
communication for all personnel, and it facilitates the
dissemination of general information to the entire
staff. If connected to the Internet, staff can
communicate with others throughout the world.
Flexible Access.
Networks allow users to access their files from
computers throughout the entire organization.

7. Workgroup Computing.
Networks allow many users to work on a document or
project concurrently. For example, architects located at
various floors within a building could simultaneously
contribute their ideas about new building complex to the
same document.
 Security
Files and programs on a network can be designated as
"copy inhibit," so that you do not have to worry about
illegal copying of programs. Also, passwords can be
established for specific directories to restrict access to
authorized users.

8. The network topology
defines the way in
which computers,
printers, and other
devices are connected.
A network topology
describes the layout of
the wire and devices as
well as the paths used
by data transmissions.

9. Therefore:
A network Topology is the physical
layout of network hardware, which
include computers, cables and other
peripherals.

10. Bus Topology
Commonly referred to as a linear bus, all
the devices on a bus topology are
connected by one single cable.

11. A bus topology consists of a main run of
cable with a terminator at each end. All
nodes (file server, workstations, and
peripherals) are connected to the linear cable
in a row.

12. Advantages of a Bus Topology
•Easy to connect a computer or peripheral to a linear bus.
•Requires less cable length than a star topology.
Disadvantages of a Bus Topology
•Entire network shuts down if there is a break in the main
cable.
•Terminators are required at both ends of the backbone cable.
•Difficult to identify the problem if the entire network shuts
down.

13. The star topology is the most commonly used
architecture in Ethernet LANs.
When installed, the star topology resembles
spokes in a bicycle wheel.
A star topology is designed with each node
(file server, workstations, and peripherals)
connected directly to a central network point
eg a hub or a switch.

15. Larger networks use the extended star topology
also called tree topology.
When used with network devices that filter frames
or packets, like bridges, switches, and routers, this
topology significantly reduces the traffic on the
wires by sending packets only to the wires of the
destination host.

16. Advantages of a Star Topology
• Easy to install and wire.
• No disruptions to the network when connecting or
removing devices.
• Easy to detect faults and to remove parts.
Disadvantages of a Star Topology
• Requires more cable length than a linear topology.
• If the hub or concentrator fails, nodes attached are
disabled.
• More expensive than linear bus topologies because of
the cost of the hubs/concentrators.

17. In a Ring topology, computers are connected so that
signals travel around the network from one computer
to another in a logical ring.


18. A frame travels around the ring,
stopping at each node. If a node
wants to transmit data, it adds the
data as well as the destination
address to the frame.
The frame then continues around the
ring until it finds the destination
node, which takes the data out of the
frame.

20. Advantages of a Ring Topology
 Equal access for all computers.
 Even performance despite many users.
Disadvantages of a Ring Topology
• Failure of one computer may impact the rest of the
network .
• Problems hard to isolate.

21. The mesh topology connects all
devices (nodes) to each other for
redundancy and fault tolerance.
It is used in WANs to interconnect
LANs and for mission critical
networks like those used by banks
and financial institutions.
Implementing the mesh topology is
expensive and difficult.

23. What would you consider when
choosing a topology?
 Cost
A bus network may be the least expensive way to install
a network; you do not have to purchase concentrators.
Length of cable needed.
The linear bus network uses shorter lengths of cable.

24. Future growth.
With a star topology, expanding a network is easily
done by adding another concentrator.
Cable type.
The most commonly used cable is unshielded twisted
pair, which is most often used with star topologies.

25. Physical Media
Interconnecting Devices
Computers
Networking Software
Applications

26. Networking media can be defined
simply as the means by which signals
(data) are sent from one computer to
another (either by cable or wireless
means).

27. HUB, Switches, Routers, Wireless
Access Points, Modems etc.

28. In a client/server network arrangement, network
services are located in a dedicated computer whose
only function is to respond to the requests of
clients.
The server contains the file, print, application,
security, and other services in a central computer
that is continuously available to respond to client
requests.

29. E-mail
Searchable Data
(Web Sites)
E-Commerce
News Groups
Internet Telephony
(VoIP)
Video
Conferencing
Chat Groups
Instant
Messengers
Internet Radio

30. Depending upon the geographical area
covered by a network, it is classified as:
Local Area Networks (LAN)
Metropolitan Area Network (MAN)
Wide Area Network (WAN)
Personal Area Network (PAN)

31. Local Area Network
A Local Area Network (LAN) is a network that is
confined to a relatively small area.
It is generally limited to a geographic area such as a
room, school, or building. Rarely are LAN computers
more than a mile apart.

32. LAN’s enable the sharing of resources such as files or
hardware devices that may be needed by multiple users
Is limited in size, typically spanning a few hundred
meters, and no more than a mile
Is fast, with speeds from 10 Mbps to 10 Gbps
Requires little wiring, typically a single cable connecting
to each device
Has lower cost compared to MAN’s or WAN’s

33. LAN’s can be either wired or wireless. Twisted pair, coax
or fibre optic cable can be used in wired LAN’s.
Every LAN uses a protocol a set of rules that governs
how packets are configured and transmitted.
Nodes in a LAN are linked together with a certain
topology. These topologies include:
Bus
Ring
Star
LANs are capable of very high transmission rates (100s
Mb/s to G b/s).

34. Speed
Cost
Security
E-mail
Resource Sharing

35. Expensive To Install
Requires Administrative Time
File Server May Fail
Cables May Break

36. A metropolitan area network(MAN) is a large computer
network that usually spans a city or a large campus.
A MAN is optimized for a larger geographical area than
a LAN, ranging from several blocks of buildings to
entire cities.
A MAN might be owned and operated by a single
organization, but it usually will be used by many
individuals and organizations.

37. A MAN often acts as a high speed network
to allow sharing of regional resources.
A MAN typically covers an area of
between 5 and 50 km diameter.
Examples of MAN: Telephone company
network that provides a high speed DSL
to customers and cable TV network.

39. WAN covers a large geographic area such as
country, continent or even whole of the world.
A WAN is two or more LANs connected
together. The LANs can be many miles
apart.
To cover great distances, WANs may
transmit data over leased high-speed phone
lines or wireless links such as satellites.

41. Multiple LANs can be connected
together using devices such as bridges,
routers, or gateways, which enable
them to share data.
The world's most popular WAN is the
Internet.

42. A PAN is a network that is used for communicating
among computers and computer devices (including
telephones) in close proximity of around a few meters
within a room.
It can be used for communicating between the devices
themselves, or for connecting to a larger network such
as the internet.
PAN’s can be wired or wireless

43. A personal area network(PAN) is a
computer network used for communication
among computer devices, including
telephones and personal digital assistants,
in proximity to an individual's body.
The devices may or may not belong to the
person in question. The reach of a PAN is
typically a few meters.