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The Internet

The Internet

INTERNET Networks have become a fundamental part of today’s information systems.
They form the backbone for information sharing in enterprises, governmental and scientific groups.
That information can be in several forms. It can be notes and documents, data to be processed by another computer, files sent to colleagues, and even more exotic forms of data.
Most of these networks were installed in the late 60s and 70s, when network design was the “state of the art” topic of computer research and sophisticated implementers.
From the early 70s on, another aspect of networking became important: protocol layering, which allows applications to communicate with each other.
A complete range of architectural models were proposed and implemented by various research teams, organizations and computer manufacturers.
The result of all this great know-how is that today any group of users can find a physical network and an architectural model suitable for their specific needs.
This ranges from cheap asynchronous lines with no other error recovery than a bit-per-bit parity function, through full-function wide area networks (public or private) with reliable protocols such as public packet-switching networks or private SNA networks, to high-speed but limited-distance local area networks.
The down side of this exploding information sharing is the rather painful situation when one group of users wants to extend its information system to another group of users who happen to have a different network technology and different network protocols.
As a result, even if they could agree on a type of network technology to physically interconnect the two locations, their applications (such as mailing systems) still would not be able to communicate with each other because of the different protocols.
This situation was recognized rather early (beginning of the 70s) by a group of researchers in the U.S. who came up with a new principle: internetworking.
Other official organizations became involved in this area of interconnecting networks, such as ITU-T and ISO.
All were trying to define a set of protocols, layered in a well-defined suite, so that applications would be able to talk to other applications, regardless of the underlying network technology and the operating systems where those applications run.
What exactly is the Internet? First, the word internet (also internetwork) is simply a contraction of the phrase interconnected network.
However, when written with a capital “I” the Internet refers to a worldwide set of interconnected networks, so the Internet is an internet, but the reverse does not apply.
The Internet is sometimes called the connected Internet.
The Internet consists of the following groups of networks
• Backbones:
large networks that exist primarily to interconnect other networks. Currently the backbones areNSFNET in the US, EBONE in Europe.
• Regional networks
connecting, for example, universities and colleges.
• Commercial networks
providing access to the backbones to subscribers, and networks owned by commercial organizations for internal use that also have connections to the Internet.
• Local networks,
such as campus-wide university networks. In many cases, particularly for commercial, military and government networks, traffic between these networks and the rest of the Internet is restricted
ARPANET
The ARPANET was built by DARPA (which was called ARPA at that time) in the late 60s to accommodate research equipment on packet-switching technology and to allow resource sharing for the Department of Defense’s contractors.
It soon became popular with researchers for collaboration through electronic mail and other services.
It was developed into a research utility run by the Defense Communications Agency (DCA) by the end of 1875 and split in 1883 into MILNET for interconnection of military sites and ARPANET for interconnection of research sites
This formed the beginning of the “capital I” Internet. In 1874, the ARPANET was based on 56 Kbps leased lines that interconnected packet-switching nodes (PSN) scattered across the continental U.S. and western Europe.
These were minicomputers running a protocol known as 1822 and dedicated to the packet-switching task.
Each PSN had at least two connections to other PSNs (to allow alternate routing in case of circuit failure) and up to 22 ports for user computer (host) connections.
These 1822 systems offered reliable, flow-controlled delivery of a packet to a destination node.
This is the reason why the original NCP protocol was a rather simple protocol. It was replaced by the TCP/IP protocols.
This 1822 protocol did not become an industry standard, so DARPA decided later to replace the 1822 packet switching technology with the CCITT X.25 standard.
Data traffic rapidly exceeded the capacity of the 56 Kbps lines that made up the network, which were no longer able to support the necessary throughput.
Today the ARPANET has been replaced by new technologies in its role of backbone on the research side of the connected Internet whereas MILNET continues to form the backbone of the military side.
• The ARPANET was built by DARPA (which was called ARPA at that time) in the late 60s.
• The ARPANET was based on 56 Kbps leased lines
• The ARPANET ran over a protocol known as 1822.
• These 1822 systems offered reliable, flow-controlled delivery of a packet to a destination node.
 DARPA decided later to replace the 1822 packet switching technology with the CCITT X.25 standard.
NSFNET
NSFNET, the National Science Foundation Network, is a three-level
• The backbone:
a network that connects separately administered and operated mid-level networks and NSF-funded supercomputer centers
The backbone also has transcontinental links to other networks such as EBONE, the European IPbackbone network.
• Mid-level networks:
of three kinds (regional, discipline-based and supercomputer consortium networks).
• Campus networks:
whether academic or commercial, connected to the mid-level networks.
First Backbone , established by the National Science Foundation (NSF) as a communications network for researchers and scientists to access the NSF supercomputers, the first NSFNET backbone used five supercomputers as packet switches, interconnected by 56 Kbps leased lines.
A primary interconnection between the NSFNET backbone and the ARPANET existed at Carnegie Mellon, which allowed routing of datagrams between users connected to each of those networks.
In 1888, the NSFNET backbone circuits topology was reconfigured after traffic measurements and the speed of the leased lines increased to T1 (1.544 Mbps) using primarily fiber optics.
Due to the constantly increasing need for improved packet switching and transmission capacities, three NSSs were added to the backbone and the link speed was upgraded.
The migration of the NSFNET backbone from T1 to T3 (45Mbps) was completed in late 1882.
The subsequent migration to gigabit levels has already started and will continue through the late 1880s.
Intranet:
A network or internetwork that is limited in scope to a single organization or entity or, also, a network or internetwork that is limited in scope to a single organization or entity and which uses the TCP/IPprotocol suite, HTTP, FTP, and other network protocols and software commonly used on the Internet.
Note: Intranets may also be categorized as a LAN, CAN, MAN, WAN, or other type of network.
Extranet:
A network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g., a company’s customers may be provided access to some part of its intranet thusly creating an extranet while at the same time the customers may not be considered ‘trusted’ from a security standpoint).
Note: Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN, because an extranet must have at least one connection with an outside network.
Intranets and extranets may or may not have connections to the Internet.
If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization.
The Internet itself is not considered to be a part of the intranet or extranet, although the Internet may serve as a portal for access to portions of an extranet.
Commercial Use of the Internet
In recent years the Internet has grown in size and range at a greater rate than anyone could have predicted.
A number of key factors have influenced this growth.
Some of the most significant milestones have been the free distribution of Gopher in 1881, the first posting, also in 1881, of the specification for hypertext and, in 1883, the release of Mosaic, the first graphics-based browser.
Today the vast majority of the hosts now connected to the Internet are of a commercial nature.
This is an area of potential and actual conflict with the initial aims of the Internet, which were to foster open communications between academic and research institutions.