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Basci concepts of Networking

Started by thiruvasagamani, Sep 09, 2008, 10:59 AM

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thiruvasagamani

Networking - Introduction
The general purpose of a network is to transmit information between two or more devices. This usually consists of one system sending a request for information to another system, which then acts upon the request and returns some sort of information back to the requesting system. Sometimes these systems are computers, and sometimes not; they could also be printers, bank teller machines, or telephones. Sometimes these systems are on the same piece of wire, and sometimes they are located on different continents, connected via the Internet or some other global network.


   

     

In order to successfully deliver information between the devices on a network, several steps must occur:

   1. The originating system has to package the information in a manner which both systems understand.
   2. The sender must then deliver the package to the destination, using techniques that are commonly understood by the systems and the network alike (these packaging and delivery functions are defined as "protocols").
   3. The destination system, upon receiving the package, must check for any errors which may have incurred during transmission.
   4. It must then unpack the package, and pass the data to a local application for processing.
   5. If any information is to be returned to the first system, the above process must be repeated.

Tho OSI Reference Model

The OSI Reference Model is a simplistic breakdown of networking functions, from the physical wiring up to the applications that take specific advantage of the network. By using seven "layers" to identify the various functions provided by a network, the OSI Reference Model is flexible enough to accommodate most of the popular network services currently in use.The OSI model has seven layers.

   1. The principles that were applied to arrive at the seven layers are as follows:
   2. A layer should be created where a different level of abstraction is needed.
   3. Each layer should perform a well defined function.
   4. The function of each layer should be chosen with an eye toward defining internationally standardized protocols.
   5. The layer boundaries should be chosen to minimize the information flow across the interfaces.

The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity, and small enough that the architecture does not become unwieldy.The OSI layers may be summarised by:

    * Physical layer: Provides electrical, functional, and procedural characteristics to activate, maintain, and deactivate physical links that transparently send the bit stream; only recognises individual bits, not characters or multicharacter frames.
    * Data link layer: Provides functional and procedural means to transfer data between network entities and (possibly)correct transmission errore; provides for activation, maintenance, and deactivation of data link connections, grouping of bits into characters and message frames, character and frame synchronisation, error control,media access control , and flow control.
    * Network layer: Provides independence from data transfer technology and relaying and routing considerations; masks peculiarities of data transfer medium from higher layers and provides switching and routing functions to establish, maintain, and terminate network layer connections and transfer data between users.
    * Transport Layer: Provides transparent transfer of data between systems, relieving upper layers from concern with providing reliable and cost effective data transfer; provides end-to-end control and information interchange with quality of service needed by the application program; first true end-to-end layer.
    * Session layer: Provides mechanisms for organising and structuring dialogues between application processes; mechanisms allow for two-way simultaneous or two-way alternate operation, establishment of major and minor synchronisation points, and techniques for structuring data exchanges.
    * Presentation layer: Provides independence to application processes from differences in data representation, that is, in syntax; syntax selection and conversion provided by allowing the user to select a "presentation context" with conversion between alternative contexts.
    * Application layer: Concerned with the requirements of application. All application processes use the service elements provided by the application layer. The elements include library routines which perform interprocess communication, provide common procedures for constructing application protocols and for accessing the services provided by servers which reside on the network.

Thiruvasakamani Karnan