Introduction

Communication between two computers over the telephone lines begun around 1968. Previously, to transfer information between equipments or computers, a vendor or a company had to rent the interface equipment from the telephone company. As this causes the delayed procedure and led to monopolizing of telephone company, the Federal communications commission (FCC) produced a rule 67, by which a vendor can directly connect an equipment to telephone company network. The device Modem was developed which converts the serial digital data form produced by a computer to a form of analog signal that can be sent through the telephone voice circuits. Thus, a communication networks enable users to transfer information in the form of voice, video, E-mail and computer files.

When a network is to transfer a stream of data from a source to destination, it must assign to the data stream a route, that is, a sequence of links or channels connecting the source to the destination. The network should also allocate the data stream a portion of the capacity or BW in each channel along the route to be used. These decisions are performed by switches (or sometimes routers) in telephone exchanges. The process is called switching. There are three types of switching namely message switching, circuit switching and packet switching. The circuit and message switching were explained in the section 4.7. The packet switching is explained in the section 11.3.

In 1978, the International Organization for Standards (ISO) was asked to come up with a solution that would allow the transparent communication and data transfer between and among systems regardless of manufacturer. The model developed by ISO is the OSI reference model. OSI stands for the open systems interconnect reference model. This model allows any two different systems to communicate regardless of their underlying architecture. The purpose of the OSI model is to open communication between different systems without requiring changes to the logic of the underlying hardware and software. In this chapter, the OSI model is described in the section 11.4.

Till 1980's, OSI model was widespread and dominated the entire networking, commercially as well as by architecture. In 1990's TCP/IP has become firmly established as the dominant commercial architecture. Now the TCP/IP is the protocol of choice in many LAN-to-WAN environments. The concepts of TCP/IP is explained in the section 11.5. LAN technologies become almost a necessity for small offices. Experts predicts that within a few years, LAN setups will find their way into homes. Various LAN technologies are explained in the section 11.6.

Asynchronous transfer mode (ATM) is a high performance, cell oriented switching and multiplexing technology that uses fixed length packets to carry different types of traffic. ATM is defined as a transport and switching method in which information does not occur periodically with some reference (hence the name asynchronous). The ATM concept is described in the section 11.7.

The internet is a social as well as a technological phenomenon. Internet is the world's largest computer network. It was created nearly twenty five years ago as ARPA net. Its goal was to create a method for widely separated computers to transfer data efficiently even in the event of nuclear attack. The internet is a network formed by the co-operative interconnection of various computing networks.

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