In the early years of computer and network research and development many systems were designed by a number of companies. Although each system had its rights and were sold across the world, it became apparent as network usage grew, that it was difficult, to enable all of these systems to communicate with each other. In the early 1980s, the International Organization for Standardization (ISO) recognized the need for a network model that would help companies create common network implementations. The OSI reference model, released in 1984, addresses this need. The OSI reference model became the primary architectural model for communications. Although other architectural models have been created, most network vendors relate their network products to the OSI reference model. The OSI model describes the processes necessary for effective communication in terms of a seven layered model. The seven layers are : Physical Layer
The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and physical connectors, are defined by physical layer specifications. Data Link Layer
The data-link layer provides error-free transfer of data frames from one computer to another over the physical layer. The layers above this layer can assume virtually error-free transmission over the network. The data-link layer provides the following functions. - Establishing and terminating a logical link between two computers identified by their unique network interface card. - Controlling frame flow by instructing the transmitting computer not to transmit frame buffers - Sequentially transmitting and receiving frames
- Providing and expecting frame-acknowledgment, and detecting and recovering from...
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