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BAJAj COACHING CENTER

INTERNET

The
Internet

is a global system of interconnected
computer networks

that use the standard
Internet Protocol
Suite

(TCP/IP) to
serve billions of users worldwide. It is a
network of networks

that consists of millions of private,
public, academic, business, and government networks of local to global scope that are linked by a broad array of
electronic and optical networking technolo
gies. The Internet carries a vast array of
information

resources and
services, most notably the inter
-
linked
hyp
ertext

documents of the
World Wide Web

(WWW) and the
infrastructure to support
electronic mail
.

ARPANET

ARPANET

(
Advanced Research Projects Agency Network
), created by the
Defense Advanced Research Projects
Agency

(DARPA) of the
United States Department of Defense
, was the world's first operational
packet switching

network, and the predecessor of the contemporary global
Internet
. The packet switching of the ARPANET was
based on designs by
Lawrence Roberts
, of the
Lincoln Laboratory
.

INTERANET

An
intranet

is a private
computer network

that uses
Internet Protocol

technologies to securely share any part of
an organization's information or operational systems within that organization. The term is used in contrast to
internet
, a network between organizations, and instead refers to a network within an organization. Sometimes
the term refers only to the organiza
tion's internal
website
, but may be a more extensive part of the
organization's information technology infrastructure. It may host multiple private websites and constitute an
important compo
nent and focal point of internal communication and collaboration.

An intranet is built from the
same concepts and technologies used for the Internet, such as
client
-
server

comput
ing and the
Internet Protocol
Suite

(TCP/IP). Any of the well known Internet protocols may be found in an intranet, such as
HTTP

(web
services),
SMTP

(e
-
mail), and
FTP

(file transfer).

URL

In
computing
, a
Uniform Resource Locator

(
URL
) is a subset of the
Uniform Resource Identifier

(URI) that
specifies where an identified resource is available and the mechanism for retrieving it.

MAC ADDRESS

In
computer networking
, a
Med
ia Access Control address

(MAC address) is a
unique identifier

assigned to most
network
adapters

or network interface cards (NICs) by the manufacturer for identification, and used in the
Media Access Control

protocol sub
-
layer. If assigned by the manuf
acturer, a MAC address usually encodes the


manufacturer's registered identification number. It may also be known as an
Ethernet Hardware Address

(EHA),
hardware address
,
adapter address
, or
physical address
.

IP ADDRESS

An
Internet Protocol

(
IP
)
address

is
a numerical label that is assigned to devices participating in a
computer network

that uses the
Internet Protocol

for communication between its nodes.An IP address
serves two principal functions: host or network interface
identifi
cation

and location
addressing
. Its role
has been characterized as follows:
"A
name

indicates what we seek
. An address indicates where it is. A
route indicates how to get there."

The designers of TCP/IP defined an IP address as a
32
-
bit

number and this system, known as
Internet
Protocol Version 4

or
IPv4
, is still in use today. However, due to the enormous growth of the Internet
and the resulting depletion of available addresses, a new addressing system (
IPv6
), using 128 bits for the
address, was developed in 1995 and last standardized by
RFC 2460

in 1998. Although IP addresses are
stored as
binary numbers
, they are usually displayed in
human
-
readable

notations, such as
208.77.188.166 (for
IPv4
), and 2001:db8:0:1234:0:567:1:1 (for
IPv6
).

IPv4 uses 32
-
bit

(4
-
byte
) addresses, which limits the
address space

to 4,294,967,296 (2
32
) possible unique
addresses. IPv4 reserves some addresses fo
r special purposes such as
private networks

(~18 million addresses)
or
multicast address
es

(~270 million addresses).


PRIVATE IP ADDRESS



Computers not connected to the Internet, such as factory machines that communicate only with each other via
TCP/IP, need not have globally
-
unique IP addresses. Three ranges of IPv4 addresses for
private networks
, one
range for each
class

(
A
,
B
,
C
). These addresses are not routed on the Internet

and thus their use need not be
coordinated with an IP address registry.



DOMAIN NAME SYSTEM

The
Domain Name System

(
DNS
) is a hierarchical naming system for computers, services, or any resource
connected to the
Internet

or a
private network
. It associates various information with
domain names

assigned to
each of the participants. Most importantly, it translates domain names meaningful to humans into the numerical
(binary) identifiers associated with networking equipment for the purpose of locatin
g and addressing these
devices worldwide. An often
-
used analogy to explain the Domain Name System is that it serves as the "
phone
book
" for the Internet by translatin
g human
-
friendly computer
hostnames

into
IP addresses
. For
example,
www.example.com

translates to
192.0.32.10
.





OSI MODEL


The
Open System Interconnection Reference Model

(OSI Reference Model or
OSI Model
) is an abstract
description for layered communications and computer
network protocol

design. It was developed as part of the
Open Systems Interconnection

(OSI
) initiative.
[1]

In its most basic form, it divides network architecture into seven
layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data Link, and
Physical Layers. It is therefore often referred to as the
OSI Seven Layer M
odel
.




TCP/IP MODEL

The
TCP/IP model

is a description framework for
computer network protocols

created in the 1970s by
DARPA
, an agency of the
United States Department of Defense
. It evolved from
ARPANET
, which was
the world's first
wide area network

and a predecessor of the
Internet
. The
TCP/IP

Model is sometimes
called the
Internet Model

or the
DoD

Model
.

The TCP/IP model, or
Internet Protocol Suite
, describes a set of general design guidelines and
implementations of specific networking p
rotocols to enable computers to communicate over a
network
.
TCP/IP provides end
-
to
-
end connectivity specifying how data should be formatted, addressed,
transmitted,
routed

and received at the destination. Protocols exist for a variety of different types of
communication services between computers.

It has 4 layers :




HOST to HOST is also some times reffered as

TRANSPORT layer.

NETWORK ACCESS a
lso known as NETWORK INTERFACE.













LAN WAN MAN





Connecting Devices:

Network interface cards

A
network card
, network adapter, or NIC (network interface card) is a piece of
computer hardware

designed to allow computers to communicate over a computer network. It provides physica
l access to a
networking medium and often provides a low
-
level addressing system through the use of
MAC
addresses
.


Repeaters

A
repeater

is an
electronic

device that receives a
signal
, cleans it from the unnecessary noise, regenerates
it and
retransmits

it at a higher power level, or to the other side of an obstruction, so that the signal can
cover longer distances

without degradation. In most twisted pair Ethernet configurations, repeaters are
required for cable which runs longer than 100 meters. Repeaters work on the Physical Layer of the OSI
model.





Hubs

A
network hub

contains multiple ports. When a packet arrives at one port, it is copied unmodified to all
ports of the hub for transmission. The destination address in the frame is not changed to a broadcast
address. It works on the Physical

Layer of the OSI model.

Bridges

A
network bridge

connects multiple
network segments

at the
data link layer

(layer 2) of the
OSI model
.
Bridges do send broadcasts to all ports except the one on whic
h the broadcast was received. However,
bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which
MAC addresses

are
reachable through specific ports. Once th
e bridge associates a port and an address, it will send traffic for
that address to that port only.

Bridges learn the association of ports and addresses by examining the source address of frames that it
sees on various ports. Once a frame arrives through a

port, its source address is stored and the bridge
assumes that MAC address is associated with that port. The first time that a previously unknown
destination address is seen, the bridge will forward the frame to all ports other than the one on which the
f
rame arrived.

Bridges come in three basic types:



Local bridges: Directly connect local area networks (LANs)



Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote
bridges, where the connecting link is slower than the end
networks, largely have been replaced
with routers.



Wireless bridges: Can be used to join LANs or connect remote stations to LANs

Switches

A
network switch

is a device that forwards and filters
OSI layer 2

datagrams

(chunk of data
communication) between ports (connec
ted cables) based on the MAC addresses in the packets.

This is
distinct from a hub in that it only forwards the frames to the ports involved in the communication rather
than all

ports connected. A switch breaks the collision domain but represents itself a broadcast domain.
Switches make forwarding decisions of frames on the basis of MAC addresses. A switch normally has
numerous ports, facilitating a star topology for devices, an
d

cascading additional switches.
Some
switches are capable of routing based on Layer 3 addressing or additional logical levels; these are called
multi
-
layer switches.

Routers
:
A
router

is a netw
orking device that forwards
packets

between networks using information in
protocol headers and forwarding tables to determine the best nex
t router for each packet.