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Emergence and history of network 

 Advanced Research Projects Agency ( ARPA) formed in 1958 .

 ARPA was formed as an agency that would be tasked by the United States

e!artment of efense (o) to research and develo! !rojects. ARPA was notre"uired to focus on only !rojects of military concern# and it was "uickly determined

that a focus on com!uters would be a worthwhile investment. $n %&'# ARPA chose

r. .*.R. +icklider to lead the com!uter research effort.

+icklider reali,ed even before his a!!ointment the !otential of connecting nodes to

one another to share resources. -e had develo!ed what he called agalactic

networkconce!t# and he was able to convince other researchers (including those

who took over when he left) how im!ortant his conce!t was. -e outlined his !lan to

accom!lish this conce!t and the very first large network research team was formed.

his team# known as theARPA community# was a grou! of universities across the

United States.

$n 1969#  ARPANET  was born. he original ARPA/0 was a network with several

small com!uters referred to as interface message processors (IMPs), which were

nodes that !erformed !acket1switching and were used to connect to each other by

modems and to users on host com!uters. he $2Ps were configured with 3 4b of 

memory# su!!orted u! to four host com!uters# and were able to connect to a

ma5imum of si5 other $2Ps. he $2Ps communicated with one another over leased

communication lines. he original ARPA/0 was made u! of four $2Ps that were

established at the following locations6

1. tanfor! Researc" Instit#te$. %ni&ersit' of aifornia, *os Angees+. %ni&ersit' of aifornia, anta ar-ara. %ni&ersit' of %ta"

77/ echnologies develo!ed the first comm#nications protoco # known as the

N Report 18$$ # which later became known as the%8 !rotocol. he %8

!rotocol sim1!ly s!ecified the manner in which a host communicated with the $2P.

he %8 !ro1tocol !redated the 9S$ reference model and did not really follow thelayering !rocess we use today. he %8 !rotocol was eventually re!laced by the

Net/or0 ontro Protoco (NP)# which incor!orated a trans!ort function. he /*P

remained the main communication !rotocol until 198+# when it was re!laced by the

TPIP pro2toco s#ite. he *P:$P !rotocol suite was more resilient than the /*P#

and its introduction was the birth of communication networks as we have known

them to date.

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3ata net/or0 

 A data network is a grou! of com!uters connected to one another by communication

!aths# as well as the standards that allow communication. A network can connect to

other networks# allowing virtually worldwide communication between two end!oints.

2any networks share information among one another# creating larger networks.

;igure %1% is an e5am!le of a segment of a network.

2any things are shared on a network. *or!orate business is conducted nearly

e5clusively on the network. /etworks allow users to share a!!li1cations that are

stored on servers in the network (e1mail a!!lications# word1!rocessing a!!lications#

databases# and many others). hey allow com1munication between end users. ata

can be shared between com!anies or individuals for business or !ersonal !ur!oses.

y!ically# networks are identified by their si,e. hey range from small local area

networks (+A/s) to larger wide area net1works (

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how data can be shared by the medical !rofession. +ab work can be returned more

"uickly# allowing for a more immediate diagnosis. 2any hos!itals are now allowing 51

rays and other data to be viewed over a network.

T"e Internet 

he $nternet was develo!ed mainly u!on its !redecessor# the Advanced Research

Projects Agency /etwork (ARPA/0). $n addition to the /etwork hardware and:or software that ca!tures data !assing

through it and determines whether to !ass or dro! the data. ;irewalls are

configurable# and filters can be a!!lied to !rovide the a!!ro!riate security for the +A/.

Public key certificate> An electronic document that can verify and authori,e

an individual by !ublic key cry!togra!hy. Public key cry!tog1ra!hy uses two

keys (one !ublic key and one !rivate key) to encry!t and then decry!t data to

ensure that a message can be trans!orted securely  Authentication encryp-tion (AE)> A system that is able to !rotect both the

secrecy and the integrity of data communication. Virtual private network (VP)> A network that is created when one net1work

connects to another by a secure tunnel.