Internet

1. The Internet, also called "the net“, is a worldwide system of
computer networks. It can be thought of as “a large computer
network” or “network of networks” in which users at any one
computer can, if they have permission, get information from any
other.
Internet

2. Internet
•The internet started by the Advanced Research projects
Administration Network (ARPANET) of the US government in
1969 with an aim to reach universities, research laboratories etc.
•However no single organization owns the internet. It is a public
and self sustaining network.
•To communicate between the different computers and
networks certain standard rules called protocols were developed
by the US dept. of defence. It is known as TCP/IP protocol
(Transmission Control protocol/Internet Protocol). Internet uses
the packet switching technology where a message is broken
into pieces called packets with each packet having the address
of the sender and receiver.

3. Networks Types
A network is a group of computers connected in some
fashion in order to share resources. Network can be
classified into following basic types-
Local Area Network (LAN)- LAN is a group of computers
located in the same room, on the same floor, or in the
same building that are connected to form a single
computer network. LANs allow users to share storage
devices, printers, applications, data and other network
resources.

4. Network Types
LANs allow users to share storage devices, printers,
applications, data and other network resources. They are
limited to a specific geographical area usually less than
one kilometre in diameter.
Wide Area Network(WAN)-WAN is used to interconnect
LANs which maybe at the opposite sides of a country or
located around the earths globe.
Metropolitan Area Network(MAN)-MAN is a network
that interconnects users with computer resources in a
geographical area or region larger than that covered by a
LAN but smaller than the area covered by a WAN.

6. Network classification
In addition to geographical area, networks are also categorized
according to architecture, topology etc.
Architecture based classification: Networks can be broadly
classified as either a peer to peer or client server architecture.
• Peer to Peer (P2P) Network- It is built without the use of a
central server and each workstation has equivalent capabilities
and responsibilities. Each peer computer can share its resources,
validate users and communicate other computers on the
network independently. P2P is simple, easy to set up and does
not require special software so it offers a cost-effective solution
for sharing files and is ideal for small business. Though they are
simpler they may not offer the same performance under heavy
load. Again, since there is no centralized control so, poor security
issues and lack of centralized data storage may happen.

7. Network classification
Client Server Network-In this type of network, transaction
responsibility is divided into two parts: client and server. A
centralized computer known as server is used to facilitate the
sharing of data, memory, database services, applications and
hardware with other computers in the network. A client is a
computer running a program that requests the service from the
server.
Beside central storage, network access, backup and network
security is controlled in this type of network. So it is more
suitable for larger network. However in client-server network, if
the server gets down all the users get affected Moreover in this
network, a special network operating system like Windows
server 2000, Windows server 2003, Netware, red hat Enterprise
Linux etc. are needed. The server is also expensive to purchase
and difficult to set up initially.

8. Network topologies
The topology of a network is the geometric arrangement of all the
links and linking devices to each other. There are four basic
topologies possible: bus, ring, star and mesh.
Bus topology- One long cable acts as a backbone to link all devices in
the network. In bus topology only one computer can send message at
a time. So this can slow down a bus network. A fault or break in the
bus cable stops all transmission even between devices on the same
side.

9. Network topologies
Ring Topology: In ring topology, each host machine connects to exactly
two other machines, creating a circular network structure. A signal is
passed along the ring in one direction, from device to device, until it
reaches its intended destination. Every computer is given equal access
to the token so no one computer can monopolize the network. Failure
of one computer on the ring affects the whole network.

10. Network topologies
Star Topology- In a star topology each device has a dedicated point to
point link only with a central controller usually called a hub. Each
device communicates only with the hub that resends the message to
the destination computer. One advantage of star network is its
robustness. If one link fails only that link is affected. All other links
remain active.

11. Network topologies
Mesh topology- In a mesh topology every device on the
network has a dedicated connection to every other device
on the network. A mesh topology is robust. If one link
becomes unusable it does not bring down the entire
network.

12. Different LAN Networks
• Ethernet- Ethernet invented in 1973 by Bob Metcalfe, is one of
the most widely implemented LAN standards. It is also used in
wireless LANs. Ethernet uses a bus or star topology Network.
Ethernet uses Carrier Sense Multiple Access/Collision
Detection (CSMA/CD) technology to detect collisions. In
CSMA/CD each device needing to send data to the network first
"listens" to the wire to determine if anyone else is sending.
Ethernet connector is a network interface card (NIC) equipped
with 48-bits MAC address.

13. Different LAN Networks
• Token Ring Topology-In this network, computer devices
are connected logically in a ring with each device
connected separately to a specialized Token Ring hub
called a Multistation Access Unit (MAU). The token ring
network passes a free token around the ring in one
consistent direction. In order to send data, a computer
device must capture a free token and encapsulate its
data within the token frame.

14. Different LAN Networks
• Fiber Distributed Data Interface (FDDI)- FDDI is a high
performance fiber optic token ring LAN running at 100 Mbps
over distances up to 200 km with up to 1000 stations connected.
FDDI cabling consists of two fiber rings-one transmitting
clockwise and the other transmitting counterclockwise. The dual
rings are used in order to avoid malfunction.

15. OSI Layer
The Open System Interconnection (OSI) model is a
communication model developed by the International
Standards Organization (ISO). It is a 7 layer communication
protocol developed to standardize the procedure for
information between different communication systems
worldwide. The 7 layers are-
1. Physical layer: It defines the actual set of wires, plugs
and electrical signals that connect the sending and
receiving devices to the network.

16. OSI Layer
2. Data Link Layer: It divides the bits received from the
network layer into frames, imposes flow and adds
reliability by adding error control to the physical layer.
3. Network layer: It provides routing mechanism to route
packets to their destination and is responsible for the
source-to-destination delivery of packets across multiple
networks. To pass a packet across different networks it
includes logical addressing system in the header of the
packet to help distinguish the source and destination
systems.

17. OSI Layer
4. Transport layer: It breaks the large messages from the
session layer into segments called packets with each
segment containing a sequence number, provides flow
control and error control.
5. Session Layer: It allows users on different machines to
establish maintain and terminate the connection called
session.

18. OSI Layer
6. Presentation layer: It translates data between the
formats the network requires and data from the
application layer. It does protocol conversion, data
translation, compression, encryption etc.
7. Application Layer: It provides user interfaces and
support for various services like e-mail, remote file access
and transfer, database access etc.

19. Communication Medium
A communication medium is a type of physical channel through which data
can be sent from one point to another. It can be wired or wireless.
Wired medium (Bounded/guided Medium)-
It is the transmission media in which signals are confined to a specific path
using wire or cable. Types of wired medium are twisted pair wire, coaxial
cable and fiber optic cable.
Twisted pair wire- It consists of two insulated copper wires that are
twisted together in a helical shape to reduce the electrical interference.

20. Unguided medium
Media in which signals are not guided through a solid medium are known as
unguided media.
Unguided or wireless media sends the data through air (or water).
Radio transmission- Its frequency is between 10 kHz to 1GHz.
Bluetooth is a wireless technology standard that uses radio waves for
exchanging data over short distances from fixed and mobile devices. Basic
range of bluetooth is 10 meters (~30 feet). A piconet is an wireless
network of devices using Bluetooth technology protocols.
Microwave Transmission- It travels at high frequency than the radio waves
with frequencies between 1and 300 GHz.
Infrared waves-
It has frequencies from 300 GHz to 400 THz can be used for short range
communication.

21. Services on Internet
Internet provides a range of services that depends on
information-
Email- Most common service of the internet. Email is a
method of sending letters, message, voice, video and
graphics over internet anywhere in the world in a cost
effective way.
Mailing List-These are group based messaging service
having a common interest. Once subscribed mailing list
messages can be received in a email account.

23. Search engines
A Search engine is a software that searches through a database of
web pages for specific information. Examples of some search engine
are-
•Google
•Yahoo
•Alta vista
•Bing
•HotBot
•Webcrawler
The starting point of all search engines is a spider (also known as
crawler, robot or bot) which visits the pages that will be included in
the search and grabs the contents of each of those pages.