The OSI model

In 1978, for open systems interconnection, available for communication with other systems, ISO (International Standard Organization) released specifications. All systems can now use the same protocols and standards for the exchange of information. In 1984, ISO released a new version of its model the OSI model (Open System Interconnection), which has become the international standard. The OSI model does not describe the services and protocols, but determines that it needs to do each level. By itself, it only serves to protocol classification. Protocol is considered to be a set of specifications defining the implementation of one or more layers of the OSI model.

The OSI model has seven levels

The OSI model has seven levels. Each level corresponds to different network operations, equipment and protocols. Certain network functions performed at each level, only interact with the functions of adjacent levels.

Each layer OSI model performs a number of operations in preparation for delivery of data over the network to another computer. All requests from one level to another is transmitted through the interface. The lowest levels determine the physical environment in the transmission of data bits through the network adapter card and cable. The uppermost levels determine how access is implemented applications to communications services.

In the OSI model, before sending a data network are divided into packets transmitted as a unit between the network devices. The package passes successively from the application to the physical level, while each level is added to the packet formatting, or address information.

On the receiving side of the package also passes through all the levels, but in reverse order. The software analyzes each level packet information, delete the information that is added to the package at the same level by the sender, and forwards the packet to the next level. Information on the computer, the sender and the receiving computer must pass all the levels, starting with the one with which it is sent, and ending with the appropriate level of the computer to which it was adopted.

The OSI model consists of the following levels. Application level manages shared access to the network, data flow and data recovery after a connection failure.

The presentation level defines the format used to exchange data between networked computers. The presentation layer is responsible for protocol conversion, translation, and data encryption.

The session level of OSI model allows two applications to different computers to establish, use and terminate the connection, called a session.

The transport level of OSI model receives the data from the session level, splits them if necessary into small parts and sends to the network level.

The network level of OSI model controls the operations of the subnet. It is responsible for addressing messages and translating logical addresses and names into physical addresses and names.

The data link level transforms the ability of the physical level to transmit data in a reliable link, free of undetected errors in terms of the higher network level.

The physical level of OSI model transmits unstructured bit stream on the physical environment (eg, network cable). The physical level generates signals which are transferred to the data received from all higher levels.