history of networking

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History of Networking

The existence of todays network is due to thecontinuous evolution in computer technology.

The first computers built in the 1950s were very bulkyand expensive and intended only for Government orUniversity use. They were not intended for interactivework between business users, nor were they used inthe packet-processing mode. As a rule, they werebuilt on a mainframe basis - a powerful and reliableroom sized server with a universal purpose. Usersprepared punch cards containing data and programcommands then transferred them to the computerservice bureau. The operators then entered thesecards into the computer, and the users receivedresults after some waiting. The overall performance ofthis expensive process (called batch jobs) was crucialto the accurate performance of its users.

In the beginning of the 1960s, simultaneously with thedecrease of the prices of processors, businesscomputerusage appeared, which took into accountthe interests of business needs and interactive multi-terminal systems for workload division. Several usersshared the mainframes resources at a time. Eachuser could work individually with the mainframethrough a terminal. The mainframes reaction timewas so quick that the user almost did not notice theparallel work with other users. With this concept, thecomputing capacity remained centralized, but some ofits functions became distributed. These multi-terminal
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systems became the ancestors of a new widelydeveloping technology, thin clients, through which allinformation processing is carried out by one powerful

computer, and the actual input/output operationsperformed by terminal stations having a minimalconfiguration of hardware and software.

In modern networks, the information processing isdivided between either clients or servers. This modelrefers to the client server relationship. The server is

the one specialized powerful computer that providesthe information that the client computers require. Theclient is the computer initiating the inquiry. Thisconcept causes concern in relation to softwaresharing, as some OSs require that one computer hasto be the server, and all computers in the networkcalled the clients. In addition, peer-to-peer networksexist where computer can be both client and/or

server.

The multi-terminal systems become a first step on thepath of creating the modern network, however, therequirement that the terminals be connected withdistant computers has gradually appeared, and thecommunications through telephone networks nowcomes through modems. (Even though the originalmeaning of modem meant modulator/demodulator,which is not performed in a straight digital connection,the devices used in xDSL and cable access are stillcalled modems). The need for an automatic exchangeof data had appeared. This mechanism relied on an
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exchange offiles, synchronizing databases, andelectronic mail between computers, (with theexception of the computer acting as the connection

terminal). The entire network services mentionedbecame traditional needs.

In the beginning of the1970s there was a lull incomputer development, and then large-scaleintegrated circuits appeared. (Up to this time,individual processors for each task were the norm, i.e.

a processor for math functions, a processor for logicfunctions, etc.) The low cost and high functionality ofthe new integrated chips resulted in the creation ofthe mini-computer, which became the real competitorto the mainframe. Ten mini-computers carried out atask in parallel faster then one mainframe and had ontop a lower overall cost.

Users now begin to realize that they would like toaccept and transfer data with neighboring computers,which started the first stages of local networks.Companies thus began connecting users to eachother, creating the first Peer-to Peer LANs. LAN(Local Area Network) is a group of workstations,PDA's (Personal Digital Assistant), terminals, printers,and other devices, incorporated into sharing a high-speed data medium that covers a relatively smallgeographic area.
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Types of networks

Different types of networks

Different types of (private) networks are distinguished

based on their size (in terms of the number of machines),

their data transfer speed, and their reach. Private networks

are networks that belong to a single organisation. There are

usually said to be three categories of networks:

LAN (local area network)

MAN (metropolitan area network) WAN (wide area network)

There are two other types of networks: TANs (Tiny Area

Network), which are the same as LANs but smaller (2 to 3

machines), and CANs (Campus Area Networks), which are

the same as MANs (with bandwidth limited between each

of the network's LANs).

LAN

LANstands forLocal Area Network. It's a group ofcomputers which all belong to the same organisation, and

which are linked within a small geographic area using a

network, and often the same technology (the most

widespread being Ethernet).

A local area network is a network in its simplest form. Datatransfer speeds over a local area network can reach up to 10

Mbps (such as for an Ethernet network) and 1 Gbps (as

with FDDI orGigabit Ethernet). A local area network can

reach as many as 100, or even 1000, users.
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By expanding the definition of a LAN to the services that it

provides, two different operating modes can be defined:

In a "peer-to-peer" network, in which communication

is carried out from one computer to another, without acentral computer, and where each computer has the

same role.

in a "client/server" environment, in which a central

computer provides network services to users.

MANs

MANs (Metropolitan Area Networks) connect multiplegeographically nearby LANs to one another (over an area

of up to a few dozen kilometres) at high speeds. Thus, a

MAN lets two remote nodes communicate as if they were

part of the same local area network.

A MAN is made from switches or routers connected to one

another with high-speed links (usually fibre optic cables).

WANs

A WAN (Wide Area Network or extended network)

connects multiple LANs to one another over great

geographic distances.

The speed available on a WAN varies depending on the

cost of the connections (which increases with distance) and

may be low.WANs operate using routers, which can "choose" the most

appropriate path for data to take to reach a network node.

The most well-known WAN is the Internet.
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Diagram of different network topologies

Diagram of different network topologies.

In computer networking, topology refers to the layout of

connected devices.

Network topology is defined as the interconnection of thevarious elements (links, nodes, etc.) of a computer network.[1][2] Network Topologies can be physical or logical.

Physical Topology means the physical design of a network

including the devices, location and cable installation.

Logical topology refers to the fact that how data actually

transfers in a network as opposed to its physical design.

Topology can be considered as a virtual shape or structureof a network. This shape actually does not correspond to

the actual physical design of the devices on the computer

network. The computers on the home network can be

arranged in a circle shape but it does not necessarily mean
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that it presents a ring topology.

Any particular network topology is determined only by the

graphical mapping of the configuration of physical and/or

logical connections between nodes. The study of networktopology uses graph theory. Distances between nodes,

physical interconnections, transmission rates, and/or signal

types may differ in two networks and yet their topologies

may be identical.

A Local Area Network(LAN) is one example of a network

that exhibits both a physical topology and a logical

topology. Any given node in the LAN has one or more links

to one or more nodes in the network and the mapping ofthese links and nodes in a graph results in a geometrical

shape that may be used to describe the physical topology of

the network. Likewise, the mapping of the data flow

between the nodes in the network determines the logical

topology of the network. The physical and logical

topologies may or may not be identical in any particular

network.

Classification of network topologies

There are also three basic categories of network topologies:

Physical topologies

Signal topologies

Logical topologies

The terms Signal topology and logical topology are often

used interchangeably, though there is a subtle difference

between the two
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Physical topologies

The mapping of the nodes of a network and the physical

connections between them i.e., the layout ofwiring,

cables, the locations of nodes, and the interconnectionsbetween the nodes and the cabling or wiring system[1].

Classification of physical topologies

Point-to-point

The simplest topology is a permanent link between two

endpoints (the line in the illustration above). Switched

point-to-point topologies are the basic model ofconventional telephony. The value of a permanent point-to-

point network is the value of guaranteed, or nearly so,

communications between the two endpoints. The value of

an on-demand point-to-point connection is proportional to

the number of potential pairs of subscribers, and has been

expressed as Metcalfe's Law.

Permanent (dedicated)Easiest to understand, of the variations of point-to-

point topology, is a point-to-point communications

channel that appears, to the user, to be permanently

associated with the two endpoints. Children's "tin-can

telephone" is one example, with a microphone to a

single public address speaker is another. These are

examples ofphysical dedicatedchannels.Within many switched telecommunications systems, it

is possible to establish a permanent circuit. One

example might be a telephone in the lobby of a public

building, which is programmed to ring only the

number of a telephone dispatcher. "Nailing down" a
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switched connection saves the cost of running a

physical circuit between the two points. The resources

in such a connection can be released when no longer

needed, for example, a television circuit from a paraderoute back to the studio.

Switched:

Using circuit-switching orpacket-switching

technologies, a point-to-point circuit can be set up

dynamically, and dropped when no longer needed.

This is the basic mode of conventional telephony.

Bus TopologyIn local area networks where bus topology is used,

each machine is connected to a single cable. Each

computer or server is connected to the single bus cable

through some kind of connector. A terminator is

required at each end of the bus cable to prevent the

signal from bouncing back and forth on the bus cable.

A signal from the source travels in both directions toall machines connected on the bus cable until it finds

the MAC address or IP address on the network that is

the intended recipient. If the machine address does not

match the intended address for the data, the machine

ignores the data. Alternatively, if the data does match

the machine address, the data is accepted. Since the

bus topology consists of only one wire, it is rather

inexpensive to implement when compared to other

topologies. However, the low cost of implementing the

technology is offset by the high cost of managing the

network. Additionally, since only one cable is utilized,

it can be the single point of failure. If the network
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cable breaks, the entire network will be down.

Linear bus

The type of network topology in which all of the

nodes of the network are connected to a commontransmission medium which has exactly two endpoints

(this is the 'bus', which is also commonly referred to as

thebackbone, ortrunk) all data that is transmitted

between nodes in the network is transmitted over this

common transmission medium and is able to be

received by all nodes in the network virtually

simultaneously (disregardingpropagation delays)[1].

Note: The two endpoints of the common transmissionmedium are normally terminated with a device called

a terminatorthat exhibits the characteristic impedance

of the transmission medium and which dissipates or

absorbs the energy that remains in the signal to

prevent the signal from being reflected or propagated

back onto the transmission medium in the opposite

direction, which would cause interference with anddegradation of the signals on the transmission medium

(See Electrical termination).

Distributed bus

The type of network topology in which all of the

nodes of the network are connected to a common

transmission medium which has more than two

endpoints that are created by adding branches to the

main section of the transmission medium the

physical distributed bus topology functions in exactly

the same fashion as the physical linear bus topology

(i.e., all nodes share a common transmission medium).

Notes:
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1.) All of the endpoints of the common transmission

medium are normally terminated with a device called

a 'terminator' (see the note under linear bus).

2.) The physical linear bus topology is sometimesconsidered to be a special case of the physical

distributed bus topology i.e., a distributed bus with

no branching segments.

3.) The physical distributed bus topology is sometimes

incorrectly referred to as a physical tree topology

however, although the physical distributed bus

topology resembles the physical tree topology, it

differs from the physical tree topology in that there isno central node to which any other nodes are

connected, since this hierarchical functionality is

replaced by the common bus.

Star topology

In local area networks with a star topology, each network

host is connected to a central hub. In contrast to the bus

topology, the star topology connects each node to the hub

with a point-to-point connection. All traffic that transverses
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the network passes through the central hub. The hub acts as

a signal booster or repeater. The star topology is considered

the easiest topology to design and implement. An

advantage of the star topology is the simplicity of addingadditional nodes. The primary disadvantage of the star

topology is that the hub represents a single point of failure.

Notes

A point-to-point link (described above) is sometimes

categorized as a special instance of the physical star

topology therefore, the simplest type of network thatis based upon the physical star topology would consist

of one node with a single point-to-point link to a

second node, the choice of which node is the 'hub' and

which node is the 'spoke' being arbitrary[1].

After the special case of the point-to-point link, as in

note 1.) above, the next simplest type of network that

is based upon the physical star topology would consistof one central node the 'hub' with two separate

point-to-point links to two peripheral nodes the

'spokes'.

Although most networks that are based upon the

physical star topology are commonly implemented

using a special device such as a hub orswitch as the

central node (i.e., the 'hub' of the star), it is alsopossible to implement a network that is based upon the

physical star topology using a computer or even a

simple common connection point as the 'hub' or

central node however, since many illustrations of the
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physical star network topology depict the central node

as one of these special devices, some confusion is

possible, since this practice may lead to the

misconception that a physical star network requiresthe central node to be one of these special devices,

which is not true because a simple network consisting

of three computers connected as in note 2.) above also

has the topology of the physical star.

Star networks may also be described as either

broadcast multi-access ornonbroadcast multi-access

(NBMA), depending on whether the technology of thenetwork either automatically propagates a signal at the

hub to all spokes, or only addresses individual spokes

with each communication.

Extended star

A type of network topology in which a network that is

based upon the physical star topology has one or morerepeaters between the central node (the 'hub' of the star)

and the peripheral or 'spoke' nodes, the repeaters being used

to extend the maximum transmission distance of the point-

to-point links between the central node and the peripheral

nodes beyond that which is supported by the transmitter

power of the central node or beyond that which is

supported by the standard upon which the physical layer of

the physical star network is based.

If the repeaters in a network that is based upon the physical

extended star topology are replaced with hubs or switches,

then a hybrid network topology is created that is referred to

as a physical hierarchical star topology, although some
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texts make no distinction between the two topologies.

Distributed Star

A type of network topology that is composed of individualnetworks that are based upon the physical star topology

connected together in a linear fashion i.e., 'daisy-chained'

with no central or top level connection point (e.g., two or

more 'stacked' hubs, along with their associated star

connected nodes or 'spokes').

Ring topology

Ring network topology

In local area networks where the ring topology is used,

each computer is connected to the network in a closed

loop or ring. Each machine or computer has a uniqueaddress that is used for identification purposes. The

signal passes through each machine or computer

connected to the ring in one direction. Ring topologies

typically utilize a token passing scheme, used to

control access to the network. By utilizing this
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scheme, only one machine can transmit on the

network at a time. The machines or computers

connected to the ring act as signal boosters or

repeaters which strengthen the signals that transversethe network. The primary disadvantage of ring

topology is the failure of one machine will cause the

entire network to fail

Mesh topology

The value of fully meshed networks is proportional to the

exponent of the number of subscribers, assuming that

communicating groups of any two endpoints, up to andincluding all the endpoints, is approximated by Reed's Law.

Fully connected mesh topology

Fully connected

Note: The physical fully connected mesh topology is

generally too costly and complex for practical

networks, although the topology is used when there

are only a small number of nodes to be interconnected.
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Partially connected mesh topology

Partially connected

The type of network topology in which some of the

nodes of the network are connected to more than one

other node in the network with a point-to-point link this makes it possible to take advantage of some of the

redundancy that is provided by a physical fully

connected mesh topology without the expense and

complexity required for a connection between every

node in the network.

Note: In most practical networks that are based upon

the physical partially connected mesh topology, all of

the data that is transmitted between nodes in thenetwork takes the shortest path (or an approximation

of the shortest path) between nodes, except in the case

of a failure or break in one of the links, in which case

the data takes an alternative path to the destination.

This requires that the nodes of the network possess

some type of logical 'routing' algorithm to determine

the correct path to use at any particular time.Tree
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Tree network topology

Also known as a hierarchical network.

The type of network topology in which a central 'root' node

(the top level of the hierarchy) is connected to one or more

other nodes that are one level lower in the hierarchy (i.e.,

the second level) with a point-to-point link between each of

the second level nodes and the top level central 'root' node,

while each of the second level nodes that are connected to

the top level central 'root' node will also have one or more

other nodes that are one level lower in the hierarchy (i.e.,

the third level) connected to it, also with a point-to-point

link, the top level central 'root' node being the only node

that has no other node above it in the hierarchy (Thehierarchy of the tree is symmetrical.) Each node in the

network having a specific fixed number, of nodes

connected to it at the next lower level in the hierarchy, the

number, being referred to as the 'branching factor' of the

hierarchical tree.

1.) A network that is based upon the physical

hierarchical topology must have at least three levels inthe hierarchy of the tree, since a network with a

central 'root' node and only one hierarchical level

below it would exhibit the physical topology of a star.

2.) A network that is based upon the physical

hierarchical topology and with a branching factor of 1
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would be classified as a physical linear topology.

3.) The branching factor, f, is independent of the total

number of nodes in the network and, therefore, if the

nodes in the network require ports for connection toother nodes the total number of ports per node may be

kept low even though the total number of nodes is

large this makes the effect of the cost of adding ports

to each node totally dependent upon the branching

factor and may therefore be kept as low as required

without any effect upon the total number of nodes that

are possible.

4.) The total number of point-to-point links in anetwork that is based upon the physical hierarchical

topology will be one less than the total number of

nodes in the network.

5.) If the nodes in a network that is based upon the

physical hierarchical topology are required to perform

any processing upon the data that is transmitted

between nodes in the network, the nodes that are athigher levels in the hierarchy will be required to

perform more processing operations on behalf of other

nodes than the nodes that are lower in the hierarchy.

Such a type of network topology is very useful and

highly recommended.

Signal topology

The mapping of the actual connections between the nodes

of a network, as evidenced by the path that the signals take

when propagating between the nodes.

Note: The term 'signal topology' is often used


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synonymously with the term 'logical topology',

however, some confusion may result from this practice

in certain situations since, by definition, the term

'logical topology' refers to the apparent path that thedata takes between nodes in a network while the term

'signal topology' generally refers to the actual path that

the signals (e.g., optical, electrical, electromagnetic,

etc.) take when propagating between nodes.

Logical topology

The logical topology, in contrast to the "physical", is

the way that the signals act on the network media, or

the way that the data passes through the network fromone device to the next without regard to the physical

interconnection of the devices. A network's logical

topology is not necessarily the same as its physical

topology. For example, twisted pair Ethernet is a

logical bus topology in a physical star topology layout.

While IBM's Token Ring is a logical ring topology, it

is physically set up in a star topology.Email

Electronic mail, most commonly abbreviated email, is a

method of exchanging digital messages across the Internet

or othercomputer networks. E-mail systems are based on a
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store-and-forward model in which e-mail server computer

systems accept, forward, deliver and store messages on

behalf of users, who only need to connect to the e-mail

infrastructure, typically an e-mail server, with a network-enabled device for the duration of message submission or

retrieval. Originally, e-mail was always transmitted directly

from one user's device to another's, but because that

required both computers to be online at the same time, this

is rarely the case nowadays.

An electronic mail message consists of two components,

the message header, and the message body, which is the

email's content. The message header contains controlinformation, including, minimally, an originator's email

address and one or more recipient addresses. Usually

additional information is added, such as a subject header

field.

Originally a text-only communications medium, email was

extended to carry multi-media content attachments, which

were standardized in with RFC 2045 through RFC 2049,collectively called, Multipurpose Internet Mail Extensions

(MIME).

The foundation for today's global Internet e-mail service

was created in the early ARPANET and standards for

encoding of messages were proposed as early as 1973

(RFC 561). An e-mail sent in the early 1970s looked very

similar to one sent on the Internet today. Conversion from

the ARPANET to the Internet in the early 1980s produced

the core of the current service.

Network-based e-mail was initially exchanged on the

ARPANET in extensions to the File Transfer Protocol

(FTP), but is today carried by the Simple Mail Transfer
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Protocol (SMTP), first published as Internet standard 10

(RFC 821) in 1982. In the process of transporting e-mail

messages between systems, SMTP communicates delivery

parameters using a message envelope separately from themessage (header and body) itself.

Origin

Electronic mail predates the inception of the Internet, and

was in fact a crucial tool in creating it.

MIT first demonstrated the Compatible Time-Sharing

System (CTSS) in 1961.[17] It allowed multiple users to loginto the IBM 7094[18] from remote dial-up terminals, and to

store files online on disk. This new ability encouraged users

to share information in new ways. E-mail started in 1965 as

a way for multiple users of a time-sharingmainframe

computerto communicate. Although the exact history is

murky, among the first systems to have such a facility were

SDC'sQ32 and MIT's CTSS.

Host-based mail systems

The original email systems allowed communication only

between users who logged into the one host or

"mainframe", but this could be hundreds or thousands of

users within a company or university. By 1966 (or earlier, it

is possible that the SAGE system had something similarsome time before), such systems allowed email between

different companies as long as they ran compatible

operating systems, but not to other dissimilar systems.

Examples include BITNET, IBM PROFS, Digital
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Equipment CorporationALL-IN-1 and the original Unix

mail.

LAN-based mail systemsFrom the early 1980s networkedpersonal computers on

LANs became increasingly important. Serverbased

systems similar to the earlier mainframe systems

developed, and again initially allowed communication only

between users logged into the same server infrastructure,

but these also could generally be linked between different

companies as long as they ran the same email system and

(proprietary) protocol.Examples include cc:Mail, WordPerfect Office, Microsoft

Mail, Banyan VINES and Lotus Notes - with various

vendors supplying gateway software to link these

incompatible systems

The rise of ARPANET mail

The ARPANET computer networkmade a largecontribution to the development of e-mail. There is one

report that indicates experimental inter-system e-mail

transfers began shortly after its creation in 1969.[20]Ray

Tomlinson is credited by some as having sent the first

email, initiating the use of the "@" sign to separate the

names of the user and the user's machine in 1971, when he

sent a message from one Digital Equipment Corporation

DEC-10 computer to another DEC-10. The two machines

were placed next to each other.[21][22] The ARPANET

significantly increased the popularity of e-mail, and it

became the killer app of the ARPANET.

Most other networks had their own email protocols and
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address formats; as the influence of the ARPANET and

later the Internet grew, central sites often hosted email

gateways that passed mail between the Internet and these

other networks. Internet email addressing is stillcomplicated by the need to handle mail destined for these

older networks. Some well-known examples of these were

UUCP (mostly Unix computers), BITNET (mostly IBM

and VAX mainframes at universities), FidoNet (personal

computers), DECNET (various networks) and CSNET a

forerunner ofNSFNet.

Operation overviewThe diagram to the right shows a typical sequence of

events[23] that takes place when Alice composes a message

using hermail user agent (MUA). She enters the e-mail

address of her correspondent, and hits the "send" button.

1. Her MUA formats the message in e-mail format and

uses the Simple Mail Transfer Protocol (SMTP) to

send the message to the local mail transfer agent

(MTA), in this case smtp.a.org, run by Alice's
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internet service provider(ISP).

2. The MTA looks at the destination address provided in

the SMTP protocol (not from the message header), in

this case [email protected]. An Internet e-mail address is a

string of the form localpart@exampledomain.

The part before the @ sign is the local partof theaddress, often the username of the recipient, and the

part after the @ sign is a domain name or a fully

qualified domain name. The MTA resolves a domain

name to determine the fully qualified domain name of

the mail exchange serverin the Domain Name System(DNS).

3. The DNS serverfor the b.org domain, ns.b.org,

responds with any MX records listing the mail

exchange servers for that domain, in this case

mx.b.org, a server run by Bob's ISP.

4. smtp.a.org sends the message to mx.b.org

using SMTP, which delivers it to the mailbox of theuserbob.

5. Bob presses the "get mail" button in his MUA, which

picks up the message using the Post Office Protocol

(POP3).

E-mail spoofingMain article: E-mail spoofing

E-mail spoofing occurs when the header information of an

email is altered to make the message appear to come from a

known or trusted source. It is often used as a ruse to collect
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personal information.

E-mail bombing

E-mail bombing is the intentional sending of large volumesof messages to a target address. The overloading of the

target email address can render it unusable and can even

cause the mail server to crash.

Privacy concerns

Main article: e-mail privacy

E-mail privacy, without some security precautions, can becompromised because:

e-mail messages are generally not encrypted.

e-mail messages have to go through intermediate

computers before reaching their destination, meaning

it is relatively easy for others to intercept and read

messages.

many Internet Service Providers (ISP) store copies ofe-mail messages on their mail servers before they are

delivered. The backups of these can remain for up to

several months on their server, despite deletion from

the mailbox.

the "Received:"-fields and other information in the e-

mail can often identify the sender, preventing

anonymous communication.

There are cryptography applications that can serve as a

remedy to one or more of the above. For example, Virtual

Private Networks or the Tor anonymity networkcan be

used to encrypt traffic from the user machine to a safer
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network while GPG, PGP, SMEmail [43] , orS/MIME can

be used forend-to-end message encryption, and SMTP

STARTTLS or SMTP overTransport Layer

Security/Secure Sockets Layer can be used to encryptcommunications for a single mail hop between the SMTP

client and the SMTP server.

Additionally, many mail user agents do not protect logins

and passwords, making them easy to intercept by an

attacker. Encrypted authentication schemes such as SASL

prevent this.

Finally, attached files share many of the same hazards as

those found inpeer-to-peer filesharing. Attached files maycontain trojans orviruses.

Tracking of sent mail

The original SMTP mail service provides limited

mechanisms for tracking a transmitted message, and none

for verifying that it has been delivered or read. It requires

that each mail server must either deliver it onward or returna failure notice (bounce message), but both software bugs

and system failures can cause messages to be lost. To

remedy this, the IETF introduced Delivery Status

Notifications (delivery receipts) and Message Disposition

Notifications (return receipts); however, these are not

universally deployed in production.

That sequence of events applies to the majority of e-mailusers. However, there are many alternative possibilities and

complications to the e-mail system:

Alice or Bob may use a client connected to a corporate

e-mail system, such as IBMLotus Notes orMicrosoft
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Exchange. These systems often have their own

internal e-mail format and their clients typically

communicate with the e-mail server using a vendor-

specific, proprietary protocol. The server sends orreceives e-mail via the Internet through the product's

Internet mail gateway which also does any necessary

reformatting. If Alice and Bob work for the same

company, the entire transaction may happen

completely within a single corporate e-mail system.

Alice may not have a MUA on her computer but

instead may connect to a webmail service. Alice's computer may run its own MTA, so avoiding

the transfer at step 1.

Bob may pick up his e-mail in many ways, for

example using the Internet Message Access Protocol,

by logging into mx.b.org and reading it directly, or

by using a webmail service.

Domains usually have several mail exchange serversso that they can continue to accept mail when the main

mail exchange server is not available.

E-mail messages are not secure ife-mail encryption is

not used correctly.

Many MTAs used to accept messages for any recipient on

the Internet and do their best to deliver them. Such MTAs

are called open mail relays. This was very important in theearly days of the Internet when network connections were

unreliable. If an MTA couldn't reach the destination, it

could at least deliver it to a relay closer to the destination.

The relay stood a better chance of delivering the message at
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a later time. However, this mechanism proved to be

exploitable by people sending unsolicited bulk e-mail and

as a consequence very few modern MTAs are open mail

relays, and many MTAs don't accept messages from openmail relays because such messages are very likely to be

spam.

Message format

The Internet e-mail message format is defined in RFC 5322

and a series ofRFCs, RFC 2045 through RFC 2049,

collectively called, Multipurpose Internet Mail Extensions,

orMIME. Although as of July 13, 2005, RFC 2822 istechnically a proposed IETF standard and the MIME RFCs

are draft IETF standards,[24] these documents are the

standards for the format of Internet e-mail. Prior to the

introduction ofRFC 2822 in 2001, the format described by

RFC 822 was the standard for Internet e-mail for nearly 20

years; it is still the official IETF standard. The IETF

reserved the numbers 5321 and 5322 for the updatedversions ofRFC 2821 (SMTP) and RFC 2822, as it

previously did with RFC 821 and RFC 822, honoring the

extreme importance of these two RFCs. RFC 822 was

published in 1982 and based on the earlierRFC 733

(see[25]).

Internet e-mail messages consist of two major sections:

Header Structured into fields such as summary,sender, receiver, and other information about the e-

mail.

Body The message itself as unstructured text;

sometimes containing a signature blockat the end.
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This is exactly the same as the body of a regular letter.

The header is separated from the body by a blank line.

Message header

Each message has exactly one header, which is structured

into fields. Each field has a name and a value. RFC 5322

specifies the precise syntax.

Informally, each line of text in the header that begins with a

printable characterbegins a separate field. The field name

starts in the first character of the line and ends before the

separator character ":". The separator is then followed bythe field value (the "body" of the field). The value is

continued onto subsequent lines if those lines have a space

or tab as their first character. Field names and values are

restricted to 7-bit ASCII characters. Non-ASCII values may

be represented using MIME encoded words.

Header fieldsThe message header should include at least the following

fields:

From: The e-mail address, and optionally the name ofthe author(s). In many e-mail clients not changeable

except through changing account settings.

To: The e-mail address(es), and optionally name(s) ofthe message's recipient(s). Indicates primary recipients(multiple allowed), for secondary recipients see Cc:

and Bcc: below.

Subject: A brief summary of the topic of the message.

Certain abbreviations are commonly used in the
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subject, including "RE:" and "FW:".

Date: The local time and date when the message was

written. Like theFrom: field, many email clients fill

this in automatically when sending. The recipient'sclient may then display the time in the format and time

zone local to him/her.

Message-ID: Also an automatically generated field;

used to prevent multiple delivery and for reference in

In-Reply-To: (see below).

Note that the To: field is not necessarily related to the

addresses to which the message is delivered. The actualdelivery list is supplied separately to the transport protocol,

SMTP, which may or may not originally have been

extracted from the header content. The "To:" field is similar

to the addressing at the top of a conventional letter which is

delivered according to the address on the outer envelope.

Also note that the "From:" field does not have to be the real

sender of the e-mail message. One reason is that it is veryeasy to fake the "From:" field and let a message seem to be

from any mail address. It is possible to digitally sign e-

mail, which is much harder to fake, but such signatures

require extra programming and often external programs to

verify. Some ISPs do not relay e-mail claiming to come

from a domain not hosted by them, but very few (if any)

check to make sure that the person or even e-mail address

named in the "From:" field is the one associated with theconnection. Some ISPs apply e-mail authentication systems

to e-mail being sent through their MTA to allow other

MTAs to detect forged spam that might appear to come

from them.
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RFC 3864 describes registration procedures for message

header fields at the IANA; it provides forpermanent and

provisional message header field names, including also

fields defined for MIME, netnews, and http, andreferencing relevant RFCs. Common header fields for

email include:

Bcc: Blind Carbon Copy; addresses added to the

SMTP delivery list but not (usually) listed in the

message data, remaining invisible to other recipients.

Cc: Carbon copy; Many e-mail clients will mark e-

mail in your inbox differently depending on whetheryou are in the To: or Cc: list.

Content-Type: Information about how the message is

to be displayed, usually a MIME type.

In-Reply-To: Message-ID of the message that this is a

reply to. Used to link related messages together.

Precedence: commonly with values "bulk", "junk", or

"list"; used to indicate that automated "vacation" or"out of office" responses should not be returned for

this mail, e.g. to prevent vacation notices from being

sent to all other subscribers of a mailinglist.

Received: Tracking information generated by mail

servers that have previously handled a message, in

reverse order (last handler first).

References: Message-ID of the message that this is a

reply to, and the message-id of the message theprevious was reply a reply to, etc.

Reply-To: Address that should be used to reply to the

message.

Sender: Address of the actual sender acting on behalf
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of the author listed in the From: field (secretary, list

manager, etc.).

Message body

Content encoding

E-mail was originally designed for 7-bit ASCII.[26] Much e-

mail software is 8-bit clean but must assume it will

communicate with 7-bit servers and mail readers. The

MIME standard introduced character set specifiers and two

content transfer encodings to enable transmission of non-

ASCII data: quoted printable for mostly 7 bit content with afew characters outside that range andbase64 for arbitrary

binary data. The 8BITMIME extension was introduced to

allow transmission of mail without the need for these

encodings but many mail transport agents still do not

support it fully. In some countries, several encoding

schemes coexist; as the result, by default, the message in a

non-Latin alphabet language appears in non-readable form(the only exception is coincidence, when the sender and

receiver use the same encoding scheme). Therefore, for

international character sets, Unicode is growing in

popularity.

Plain text and HTML

Most modern graphic e-mail clients allow the use of eitherplain text orHTML for the message body at the option of

the user. HTML e-mail messages often include an

automatically-generated plain text copy as well, for

compatibility reasons.
http://en.wikipedia.org/wiki/ASCIIhttp://en.wikipedia.org/wiki/E-mail#cite_note-25http://en.wikipedia.org/wiki/8-bit_cleanhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/Quoted_printablehttp://en.wikipedia.org/wiki/Base64http://en.wikipedia.org/wiki/8BITMIMEhttp://en.wikipedia.org/wiki/Mail_transport_agenthttp://en.wikipedia.org/wiki/Character_sethttp://en.wikipedia.org/wiki/Unicodehttp://en.wikipedia.org/wiki/E-mail_clienthttp://en.wikipedia.org/wiki/Plain_texthttp://en.wikipedia.org/wiki/HTMLhttp://en.wikipedia.org/wiki/ASCIIhttp://en.wikipedia.org/wiki/E-mail#cite_note-25http://en.wikipedia.org/wiki/8-bit_cleanhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/Quoted_printablehttp://en.wikipedia.org/wiki/Base64http://en.wikipedia.org/wiki/8BITMIMEhttp://en.wikipedia.org/wiki/Mail_transport_agenthttp://en.wikipedia.org/wiki/Character_sethttp://en.wikipedia.org/wiki/Unicodehttp://en.wikipedia.org/wiki/E-mail_clienthttp://en.wikipedia.org/wiki/Plain_texthttp://en.wikipedia.org/wiki/HTML


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Advantages of HTML include the ability to include in-line

links and images, set apart previous messages inblock

quotes, wrap naturally on any display, use emphasis such as

underlines and italics, and change font styles.Disadvantages include the increased size of the email,

privacy concerns about web bugs, abuse of HTML email as

a vector forphishing attacks and the spread ofmalicious

software.[27]

Some web based Mailing lists recommend that all posts be

made in plain-text[28][29] for all the above reasons, but also

because they have a significant number of readers using

text-basede-mail clients such as Mutt.Some Microsofte-mail clients allow rich formatting using

RTF, but unless the recipient is guaranteed to have a

compatible e-mail client this should be avoided.[30]

In order to ensure that HTML sent in an email is rendered

properly by the recipient's client software, an additional

header must be specified when sending: "Content-type:

text/html". Most email programs send this headerautomatically.
http://en.wikipedia.org/wiki/Block_quotehttp://en.wikipedia.org/wiki/Block_quotehttp://en.wikipedia.org/wiki/Underlinehttp://en.wikipedia.org/wiki/Italicshttp://en.wikipedia.org/wiki/Fonthttp://en.wikipedia.org/wiki/Web_bughttp://en.wikipedia.org/wiki/Phishinghttp://en.wikipedia.org/wiki/Malwarehttp://en.wikipedia.org/wiki/Malwarehttp://en.wikipedia.org/wiki/E-mail#cite_note-26http://en.wikipedia.org/wiki/Mailing_listhttp://en.wikipedia.org/wiki/E-mail#cite_note-27http://en.wikipedia.org/wiki/E-mail#cite_note-28http://en.wikipedia.org/wiki/Text_user_interfacehttp://en.wikipedia.org/wiki/E-mail_clienthttp://en.wikipedia.org/wiki/Mutt_(e-mail_client)http://en.wikipedia.org/wiki/Microsofthttp://en.wikipedia.org/wiki/E-mail_clienthttp://en.wikipedia.org/wiki/Rich_Text_Formathttp://en.wikipedia.org/wiki/E-mail_clienthttp://en.wikipedia.org/wiki/E-mail#cite_note-29http://en.wikipedia.org/wiki/Block_quotehttp://en.wikipedia.org/wiki/Block_quotehttp://en.wikipedia.org/wiki/Underlinehttp://en.wikipedia.org/wiki/Italicshttp://en.wikipedia.org/wiki/Fonthttp://en.wikipedia.org/wiki/Web_bughttp://en.wikipedia.org/wiki/Phishinghttp://en.wikipedia.org/wiki/Malwarehttp://en.wikipedia.org/wiki/Malwarehttp://en.wikipedia.org/wiki/E-mail#cite_note-26http://en.wikipedia.org/wiki/Mailing_listhttp://en.wikipedia.org/wiki/E-mail#cite_note-27http://en.wikipedia.org/wiki/E-mail#cite_note-28http://en.wikipedia.org/wiki/Text_user_interfacehttp://en.wikipedia.org/wiki/E-mail_clienthttp://en.wikipedia.org/wiki/Mutt_(e-mail_client)http://en.wikipedia.org/wiki/Microsofthttp://en.wikipedia.org/wiki/E-mail_clienthttp://en.wikipedia.org/wiki/Rich_Text_Formathttp://en.wikipedia.org/wiki/E-mail_clienthttp://en.wikipedia.org/wiki/E-mail#cite_note-29


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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 technologies. TheInternet carries a vast array ofinformation resources and

services, most notably the inter-linked hypertext documents

of the World Wide Web (WWW) and the infrastructure to

support electronic mail.

Most traditional communications media, such as telephone
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and television services, are reshaped or redefined using the

technologies of the Internet, giving rise to services such as

Voice over Internet Protocol (VoIP) and IPTV. Newspaper

publishing has been reshaped into Web sites,blogging, andweb feeds. The Internet has enabled or accelerated the

creation of new forms of human interactions through

instant messaging, Internet forums, and social networking

sites.

The origins of the Internet reach back to the 1960s when

the United States funded research projects of its military

agencies to build robust, fault-tolerant and distributed

computer networks. This research and a period of civilianfunding of a new U.S.backbone by theNational Science

Foundation spawned worldwide participation in the

development of new networking technologies and led to the

commercialization of an international network in the mid

1990s, and resulted in the following popularization of

countless applications in virtually every aspect of modern

human life. As of 2009, an estimated quarter of Earth'spopulation uses the services of the Internet.

The Internet has no centralized governance in either

technological implementation or policies for access and

usage; each constituent network sets its own standards.

Only the overreaching definitions of the two principal name

spaces in the Internet, the Internet Protocol address space

and the Domain Name System, are directed by a maintainer

organization, the Internet Corporation for Assigned Names

and Numbers (ICANN). The technical underpinning and

standardization of the core protocols (IPv4 and IPv6) is an

activity of the Internet Engineering Task Force (IETF), a

non-profit organization of loosely affiliated international
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participants that anyone may associate with by contributing

technical expertise.

History

Main article: History of the Internet

The USSR's launch ofSputnikspurred the United States to

create the Advanced Research Projects Agency (ARPA or

DARPA) in February 1958 to regain a technological lead.[2]

[3] ARPA created the Information Processing Technology

Office (IPTO) to further the research of the Semi AutomaticGround Environment (SAGE) program, which had

networked country-wide radarsystems together for the first

time. The IPTO's purpose was to find ways to address the

US Military's concern about survivability of their

communications networks, and as a first step interconnect

their computers at the Pentagon, Cheyenne Mountain, and

SAC HQ. J. C. R. Licklider, a promoter of universal

networking, was selected to head the IPTO. Licklidermoved from the Psycho-Acoustic Laboratory at Harvard

University to MIT in 1950, after becoming interested in

information technology. At MIT, he served on a committee

that established Lincoln Laboratory and worked on the

SAGE project. In 1957 he became a Vice President at BBN,

where he bought the first production PDP-1 computer and

conducted the first public demonstration oftime-sharing.

ProfessorLeonard Kleinrockwith one of the first

ARPANET Interface Message Processors at UCLA
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At the IPTO, Licklider's successorIvan Sutherland in 1965

got Lawrence Roberts to start a project to make a network,

and Roberts based the technology on the work ofPaulBaran,[4] who had written an exhaustive study for the

United States Air Force that recommendedpacket

switching (opposed to circuit switching) to achieve better

network robustness and disaster survivability. Roberts had

worked at the MIT Lincoln Laboratory originally

established to work on the design of the SAGE system.

UCLA professorLeonard Kleinrockhad provided the

theoretical foundations for packet networks in 1962, andlater, in the 1970s, forhierarchical routing, concepts which

have been the underpinning of the development towards

today's Internet.

Sutherland's successorRobert Taylorconvinced Roberts to

build on his early packet switching successes and come and

be the IPTO Chief Scientist. Once there, Roberts prepared a

report called Resource Sharing Computer Networks whichwas approved by Taylor in June 1968 and laid the

foundation for the launch of the working ARPANET the

following year.

After much work, the first two nodes of what would

become the ARPANET were interconnected between

Kleinrock's Network Measurement Center at the UCLA's

School of Engineering and Applied Science and Douglas

Engelbart's NLS system at SRI International (SRI) in

Menlo Park, California, on October 29, 1969. The third site

on the ARPANET was the Culler-Fried Interactive

Mathematics centre at the University of California at Santa

Barbara, and the fourth was the University of Utah
http://en.wikipedia.org/wiki/Ivan_Sutherlandhttp://en.wikipedia.org/wiki/Lawrence_Roberts_(scientist)http://en.wikipedia.org/wiki/Paul_Baranhttp://en.wikipedia.org/wiki/Paul_Baranhttp://en.wikipedia.org/wiki/Internet#cite_note-3http://en.wikipedia.org/wiki/United_States_Air_Forcehttp://en.wikipedia.org/wiki/Packet_switchinghttp://en.wikipedia.org/wiki/Packet_switchinghttp://en.wikipedia.org/wiki/Circuit_switchinghttp://en.wikipedia.org/wiki/MIT_Lincoln_Laboratoryhttp://en.wikipedia.org/wiki/Leonard_Kleinrockhttp://en.wikipedia.org/wiki/Hierarchical_routinghttp://en.wikipedia.org/wiki/Robert_Taylor_(computer_scientist)http://en.wikipedia.org/wiki/ARPANEThttp://en.wikipedia.org/wiki/Henry_Samueli_School_of_Engineering_and_Applied_Sciencehttp://en.wikipedia.org/wiki/Henry_Samueli_School_of_Engineering_and_Applied_Sciencehttp://en.wikipedia.org/wiki/Douglas_Engelbarthttp://en.wikipedia.org/wiki/Douglas_Engelbarthttp://en.wikipedia.org/wiki/SRI_Internationalhttp://en.wikipedia.org/wiki/Menlo_Park,_Californiahttp://en.wikipedia.org/wiki/University_of_Utahhttp://en.wikipedia.org/wiki/Ivan_Sutherlandhttp://en.wikipedia.org/wiki/Lawrence_Roberts_(scientist)http://en.wikipedia.org/wiki/Paul_Baranhttp://en.wikipedia.org/wiki/Paul_Baranhttp://en.wikipedia.org/wiki/Internet#cite_note-3http://en.wikipedia.org/wiki/United_States_Air_Forcehttp://en.wikipedia.org/wiki/Packet_switchinghttp://en.wikipedia.org/wiki/Packet_switchinghttp://en.wikipedia.org/wiki/Circuit_switchinghttp://en.wikipedia.org/wiki/MIT_Lincoln_Laboratoryhttp://en.wikipedia.org/wiki/Leonard_Kleinrockhttp://en.wikipedia.org/wiki/Hierarchical_routinghttp://en.wikipedia.org/wiki/Robert_Taylor_(computer_scientist)http://en.wikipedia.org/wiki/ARPANEThttp://en.wikipedia.org/wiki/Henry_Samueli_School_of_Engineering_and_Applied_Sciencehttp://en.wikipedia.org/wiki/Henry_Samueli_School_of_Engineering_and_Applied_Sciencehttp://en.wikipedia.org/wiki/Douglas_Engelbarthttp://en.wikipedia.org/wiki/Douglas_Engelbarthttp://en.wikipedia.org/wiki/SRI_Internationalhttp://en.wikipedia.org/wiki/Menlo_Park,_Californiahttp://en.wikipedia.org/wiki/University_of_Utah


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Graphics Department. In an early sign of future growth,

there were already fifteen sites connected to the young

ARPANET by the end of 1971.

The ARPANET was one of the "eve" networks of today'sInternet. In an independent development, Donald Davies at

the UK National Physical Laboratory also discovered the

concept of packet switching in the early 1960s, first giving

a talk on the subject in 1965, after which the teams in the

new field from two sides of the Atlantic ocean first became

acquainted. It was actually Davies' coinage of the wording

"packet" and "packet switching" that was adopted as the

standard terminology. Davies also built a packet switchednetwork in the UK called the Mark I in 1970. [5]

Following the demonstration that packet switching worked

on the ARPANET, the British Post Office, Telenet,

DATAPAC and TRANSPAC collaborated to create the first

international packet-switched network service. In the UK,

this was referred to as the International Packet Switched

Service (IPSS), in 1978. The collection ofX.25-basednetworks grew from Europe and the US to cover Canada,

Hong Kong and Australia by 1981. The X.25 packet

switching standard was developed in the CCITT (now

called ITU-T) around 1976.
http://en.wikipedia.org/wiki/Donald_Davieshttp://en.wikipedia.org/wiki/National_Physical_Laboratory_(United_Kingdom)http://en.wikipedia.org/wiki/Internet#cite_note-4http://en.wikipedia.org/wiki/General_Post_Office_(United_Kingdom)http://en.wikipedia.org/wiki/Telenethttp://en.wikipedia.org/wiki/DATAPAChttp://en.wikipedia.org/wiki/International_Packet_Switched_Servicehttp://en.wikipedia.org/wiki/International_Packet_Switched_Servicehttp://en.wikipedia.org/wiki/1978_in_sciencehttp://en.wikipedia.org/wiki/X.25http://en.wikipedia.org/wiki/Hong_Konghttp://en.wikipedia.org/wiki/ITU-Thttp://en.wikipedia.org/wiki/Donald_Davieshttp://en.wikipedia.org/wiki/National_Physical_Laboratory_(United_Kingdom)http://en.wikipedia.org/wiki/Internet#cite_note-4http://en.wikipedia.org/wiki/General_Post_Office_(United_Kingdom)http://en.wikipedia.org/wiki/Telenethttp://en.wikipedia.org/wiki/DATAPAChttp://en.wikipedia.org/wiki/International_Packet_Switched_Servicehttp://en.wikipedia.org/wiki/International_Packet_Switched_Servicehttp://en.wikipedia.org/wiki/1978_in_sciencehttp://en.wikipedia.org/wiki/X.25http://en.wikipedia.org/wiki/Hong_Konghttp://en.wikipedia.org/wiki/ITU-T


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A plaque commemorating the birth of the Internet at

Stanford University

X.25 was independent of the TCP/IP protocols that arose

from the experimental work of DARPA on the ARPANET,

Packet Radio Net and Packet Satellite Net during the same

time period.

The early ARPANET ran on theNetwork Control Program

(NCP), a standard designed and first implemented in

December 1970 by a team called the Network WorkingGroup (NWG) led by Steve Crocker. To respond to the

network's rapid growth as more and more locations

connected, Vinton Cerfand Robert Kahn developed the

first description of the now widely used TCP protocols

during 1973 and published a paper on the subject in May

1974. Use of the term "Internet" to describe a single global

TCP/IP networkoriginated in December 1974 with the

publication ofRFC 675, the first full specification of TCP

that was written by Vinton Cerf, Yogen Dalal and Carl

Sunshine, then at Stanford University. During the next nine

years, work proceeded to refine the protocols and to

implement them on a wide range of operating systems. The
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first TCP/IP-based wide-area network was operational by

January 1, 1983 when all hosts on the ARPANET were

switched over from the older NCP protocols. In 1985, the

United States'National Science Foundation (NSF)commissioned the construction of theNSFNET, a

history of networking

Documents