The open system interconnection

The open system interconnection (OSI) model defines a networking frame to implement protocols in seven layers. Use this helpful guide to distinguish other layer of the OSI model and understand how they interact  with each other. The history of growth of the OSI model is, for some excuse, a little known story, most of the work of OSI made by honeywell, with expert product planning and the desaign and growth of prototype systems. OSI works by sending data from top layer necessarily to be passed down and in input the capacity of a PDU in bottom layer. In the real world, the process of encapsulation (adding a header ) doesn't always occur at all layers and sometimes things get chopped into smaller pieces so they will be easier to send and receive . OSI layer is created by the OSI in 1970 as it was before OSI protocols that there is a named Dod but only used by government departments of defences.  Then OSI model has seven layers with the bottom layer of the sequence is the physical, data link, network, transport, session, presentation and user application .

            Definition of the OSI model is a network device used to implement protocols in seven layers. The control usage is passed from one layer to the next.

            History of OSI is initiated at the end of 1970’s, two projects started independently, with the same purpose to define standards. The network system architecture is given by the international organization for standardization (ISO), while others are conducted by international telegraph and telephone consultations Steering Comittee, or CCIT (the abbreviation of the French version) .These two international standards bodies were each developed a document that defined the same model network . In 1983 the two documents are merged to form a so-called standard model of elementary reference to standard OSI usually referred to a model OSI reference, the OSI reference model or models of OSI are only published in 1984 by the ISO, as standard ISO 7498 and renamed CCITT (or now called the telecommunication standardization sector of international telecommunication union or ITU-T) as standard x 200.

            The work method of the OSI is started from the top layer should be lowered and put into a payload of the PDU to the layer below it, in the real world, the process of encapsulation (add header) does not always occurs in all walks of life and sometimes things that can be cut into small so they will be easier to sent and receiving data passes through the internet, so it gets the first header of the application, then on the Transmission Control Protocol (TCP), the Internet Protocol (IP) to add headers and shared to the physical connection.

            The difference between OSI and DOD is the layers. DOD has only 4 layers but DOD models also have the same functionality as the OSI session layer. DOD is combining and presentating layer in the OSI application layer while to differentiate into specific layers.

            The main purpose of usage of the OSI model is to help network designers understand the function of each layer associated with the flow of data communication. The bottom layer is the physical layer that used to define the network transmission medium, signaling method, bit synchronization, network architecture, network topology and cabling. The next layer is the data link layer that used to determine how the data bits are grouped to format called frames. Data link layer after that layer is a layer that used in Networking to define IP addresses, create a header for packets, and perform routing through internetworking with using routers and layer 3 switches Networking layer. The next layer is the transport layer that serves to break down the data into the data packets and provide the serial number to those packages that can be rearranged on the side of the goal after receipt. Then the next layer is the Session layer which serves to define how the connection can be made, kept, or destroyed. Then the next layer is the presentation layer that serves to translate the data to be transmitted by the application into a format that can be transmitted over the network. Then the last layer is the application layer which serves to explain specifically to the scope in which network applications communicate with network services and provide services for the user application or can be used to interface with applications to network functionality, set how applications can access the network and create error messages .

            In general, the protocol has a function to connect the receiver side and to communicate and exchange information in shipping, OSI Data send it step by step depending the sequence 7 layers exist.