Computer network

Computer Network

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Network

A network is a series of points or nodes
interconnected by communication paths.
Networks can interconnect with other
networks and contain sub networks.


What is a computer network?

• A group of geographically distributed computers
which are interconnected using communication
lines in such a way that any computer in the
group may be accessed or used from any other
computer in the group.
• Interconnection of two or more computers and
peripherals.


• Computer Networking is basically the
process of connecting two or more
computers or devices, using hardware and
software, so that data can be transferred
and shared between them.


Computer Networks:

• Facilitate communications
• Permit sharing of files, data, and other
types of information
• Share network and computing resources
• May be insecure
• May interfere with other technologies
• May be difficult to set up


What A Network Includes:

• Transmission Hardware
- NIC (Network interface
controller), MODEM, Other transmitter
• Intermediate hardware devices
-
Hub, Repeaters, Amplifiers, Switch, Router, Fire
walls
• Protocol software
- encodes and formats data
- detects and corrects problems

Communication media

• Computer networks can be classified
according to the hardware and associated
software technology that is used to
interconnect the individual devices in the
network, such as electrical cable
(HomePNA, power line
communication), optical fiber, and radio
waves (wireless LAN).


Communication media

Wired technologies
• Twisted pair wire is the most widely used
medium for telecommunication. Twisted-
pair cabling consist of copper wires that
are twisted into pairs. Ordinary telephone
wires consist of two insulated copper wires
twisted into pairs.
• Coaxial cable is widely used for cable
television systems, office buildings, and
other work-sites for local area networks. Page 8
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Communication media

• Optical fiber cable consists of one or more
filaments of glass fiber wrapped in
protective layers that carries data by
means of pulses of light. It transmits light
which can travel over extended distances.
Fiber-optic cables are not affected by
electromagnetic radiation.


Communication media

Wireless technologies
• Terrestrial microwave – Terrestrial microwaves
use Earth-based transmitter and receiver. The
equipment looks similar to satellite dishes.
Terrestrial microwaves use low-gigahertz
range, which limits all communications to line-of-
sight. Path between relay stations spaced
approx, 48 km (30 mi) apart. Microwave
antennas are usually placed on top of
buildings, towers, hills, and mountain peaks.

Terrestrial microwave dish


Communication media

• Communications satellites – The satellites
use microwave radio as their
telecommunications medium which are not
deflected by the Earth's atmosphere. The
satellites are stationed in space, typically
35,400 km (22,000 mi) (for
geosynchronous satellites) above the
equator. These Earth-orbiting systems are
capable of receiving and relaying
voice, data, and TV signals.

Communications satellite


Communication media

• Cellular and PCS systems – Use several
radio communications technologies. The
systems are divided to different
geographic areas. Each area has a low-
power transmitter or radio relay antenna
device to relay calls from one area to the
next area.


PCS cellular systems


Communication media

• Wireless LANs – Wireless local area
network use a high-frequency radio
technology similar to digital cellular and a
low-frequency radio technology. Wireless
LANs use spread spectrum technology to
enable communication between multiple
devices in a limited area. An example of
open-standards wireless radio-wave
technology is IEEE 802.11.

Communication media

• Infrared communication can transmit signals
between devices within small distances of
typically no more than 10 meters.
• A global area network (GAN) is a network used
for supporting mobile across an arbitrary number
of wireless LANs, satellite coverage areas, etc.
The key challenge in mobile communications is
handing off the user communications from one
local coverage area to the next. In IEEE Project
802, this involves a succession of terrestrial
wireless LANs. Free Powerpoint Templates Page 17

Types of Computer Networks

• Networks are classified depending on the
geographical area covered by the network:
1. Local Area Network or LAN
2. Metropolitan Area Network or MAN
3. Wide Area Network or WAN
4. Wireless Networks
5. Internetworks


Local Area Network

• is a network that connects computers and
devices in a limited geographical area
such as home, school, computer
laboratory, office building, or closely
positioned group of buildings. Each
computer or device on the network is a
node.
• covers a small area


• Computers connected to a network are broadly
categorized as servers or workstations.
• Servers are generally not used by humans
directly, but rather run continuously to provide
"services" to the other computers (and their
human users) on the network. Services provided
can include printing and faxing, software
hosting, file storage and
sharing, messaging, data storage and
retrieval, complete access control (security) for
the network's resources, and many others.

• Workstations are called such because they
typically do have a human user which interacts
with the network through them. Workstations
were traditionally considered a
desktop, consisting of a
computer, keyboard, display, and mouse, or a
laptop, with integrated keyboard, display, and
touchpad. With the advent of the tablet
computer, and the touch screen devices such as
iPad and iPhone, our definition of workstation is
quickly evolving to include those
devices, because of their ability to interact with
the network and Free Powerpoint Templates
utilize network services. Page 21

Local Area Network
Advantages of connecting computers in a LAN:
• workstations can share peripheral devices
like printers. This is cheaper than buying a
printer for every workstations.
• User can save their work centrally on the
network file server. This means that they
can retrieve their work from any
workstation on the network. They don’t
need to go back to the same workstation
all the time.

Advantages of connecting computers in a LAN:

• User can communicate with each other
and transfer data between workstations
very easily.
• One copy of each application package
such as word processor, spreadsheet ect.
can loaded onto the file and shared by all
users. When a new version comes out, it
only has to be loaded onto the server
instead of onto every workstation.

Disadvantages of connecting computers in a
LAN

• 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 or
MAN
• A metropolitan area network (MAN) is a
computer network that usually spans a city
or a large campus. A MAN usually
interconnects a number of local area
networks (LANs) using a high-capacity
backbone technology, such as fiber-optical
links, and provides up-link services to wide
area networks (or WAN) and the Internet.


Wide Area Network or WAN

• A wide area network (WAN) is a
computer network that covers a large
geographic area such as a city, country, or
spans even intercontinental
distances, using a communications
channel that combines many types of
media such as telephone
lines, cables, and air waves. A WAN often
uses transmission facilities provided by
common carriers,Powerpointas telephone
Free such Templates Page 26

Wireless Network
• Wireless network refers to any type of
computer network that is not connected by
cables of any kind. It is a method by which
homes, telecommunications networks and
enterprise (business) installations avoid the
costly process of introducing cables into a
building, or as a connection between various
equipment locations. Wireless
telecommunications networks are generally
implemented and administered using a
transmission system called radio waves. This
implementation takes place at the physical level
(layer) of the network structure.

Internetwork

• An internetwork is the connection of
multiple computer networks via a common
routing technology using routers. The
Internet is an aggregation of many
connected internetworks spanning the
Earth.


Networks may also be different in their design and layout.
There are client/server networks and peer-to-peer
networks.
• A computer network is referred to as client/server if (at
least) one of the computers is used to "serve" other
computers referred to as "clients".
• In a client/server environment, each computer still holds
(or can still hold) its (or some) resources and files. Other
computers can also access the resources stored in a
computer, as in a peer-to-peer scenario. One of the
particularities of a client/server network is that the files
and resources are centralized. This means that a
computer, the server, can hold them and other
computers can access them. Since the server is always
On, the client machines can access the files and
resources without caring whether a certain computer is
On.

Client/Server Networking


• In a peer-to-peer network, each computer
holds its files and resources. Other
computers can access these resources
but a computer that has a particular
resource must be turned on for other
computers to access the resource it has.
For example, if a printer is connected to
computer A and computer B wants to
printer to that printer, computer A must be
turned On. Free Powerpoint Templates Page 31

Peer-to-Peer Networking


Computer network

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