SRI LANKAN SONGS
InIntroduction to Internet
A network is a collection of computers interconnected through some physical medium so that they can communicate. This physical medium can be a copper cable, fiber optic cable, or a wireless medium such as electromagnetic waves (light, radio waves, etc..). We cab classify these networks depending on their geographical extent; a Local Area Networks (LAN) spreads over a limited geographical area and in contrast a Wide Area Network (WAN) connects computers over a much larger geographic area.
An internetwork connects independent LANs and WANs to form one large network. Such a network is called an internet. There is one such global internet that stemmed from an experimental network started by the advanced research project agency of the United States Department of Defense in 1960s. Now this network spans over political and geographical boundaries. That particular internet is called the Internet. When we refer to this particular internetwork we always capitalize the first letter “I”. The individual networks on the internet are administered and owned by different persons and organizations and they use different technologies to connect computers. The internet uses different technologies to connect these networks together; some networks are connected to each other over a public telephone networks while others are connected over satellite links.
It is wonder that computers communicate over this widely diverse and most often incompatible collection of networks. This is possible because of a common set of rules that they all adhere to despite the differences in the individual LAN or WAN technologies. Such a set of rules used for communication is called a protocol and the protocol used in the internet is called the TCP/IP protocol suite.
that they all adhere to despite the differences in the individual LAN or WAN technologies. Such a set of rules used for communication is called a protocol and the protocol used in the internet is called the TCP/IP protocol suite.
The internet is a giant network spread thorugh out the world by connecting different types/levels of computers (from personal computers to high end work-stations) Although these computers are at homes, offices, schools/universities and government departments, it apperars as an information retrieval system with communication facilities to all users of the Internet. At the same time, it is a system which is available on demand at all times.
Not like the telephone system which has very limited number of services (voice phone, fax etc..), the internet has unlimited number of services. At the same time, these services can be offered simultaneously (multi tasking environment) based on the users demand. Applications which run (execute) at computers connected to the internet can provide these services.
Early years of the Internet
In the early years of the internet, by the late 1970s many independent LAN networks were emerged due to two reasons. First is due to the introduction of the inexpensive minicomputers. Second reason is introduction ot the inexpensive easy to install LAN technologies. LAN technologies solve the problem of computer communication in a way that is inexpensive and reliable.
LAN technology changed the way people worked by enabling resource sharing. Before LAN technologies, each computer had specific input/output devices like printers and one copy of the data or software. But with the introduction of the LAN technology a set of computers could share resources like printers. As there were many different LAN technologies companies installed the LAN technology that best met their needs. Most large organizations had several LAN technology in use in different departments.
Suppose an organization has two LANs one in the accounting department and one in the Human Resource division. If one needs to transfer information that is stored on a computer in the HR division to a computer in the accounting department connecting the two cables may not make it possible if the two LANs are using different technologies. So there was a problem in sharing information between different LANs.
Emergence of WANs
It is not always possible to connect multiple LANs together as different LAN technologies can be incompatible. In 1960s and 1970s scientists came out with WANs that connected multiple computers across large geographical distances. So with this a company with offices in several cities can install a WAN that links computers in each city. All attached computers can communicate with each other. However WANs cost much more than LANs. Hence LANs were much popular than WANs Engineers invented many WAN technologies most of them were incompatible with one another.
A single Network
Still there were many problems in accessing resources. For example, say in an organization if one computer attaches to a LAN and another attaches to a Wan, neither has access to all resources in the organization. The goal was to all resources, with some restrictions on the resources a given computer or user can access.
By the late 1970s, the U.S. department of Defense through Advanced Research Project Agency (ARPA) had several computer networks to pass technology on to the military. Its goal was to support military research about how to build a network that could continue to function in the midst of partial outages that could be caused by bomb attacks. It included a WAN called ARPANET. ARPA also had the same problem in sharing resources. ARPA research examined how to interconnect all machines to form a large single network.
Internet Standards: TCP/IP
Internet standards forms an important part of the technology that makes it possible to interconnect networks. Two pieces of the Internet standards are, The Internet Protocol software which provides basic communication, Transmission Control Protocol software which provides additional facilities that applications need.
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