The OSI (Open Systems Interconnection) networking model has been developed by ISO as a standard and universal set of specifications that would help and simplify communication between computers through the network.
The OSI networking model is splitting network communication into seven layers. Each layer has different protocols designed to perform specific tasks while interacting only with layers below and above.While top layer is interacting with the software, the bottom layer is used for sending and receiving signal through the cable. The protocols for each layer are simply pre-defined sets of rules and tasks that should be performed.
The network layers are designed in a way that every network process could be assigned to the layer. The layers are: Physical, Data Link, Network, Transport, Session, Presentation, and Application. The model does not specify hardware requirements for network communication as well as software necessary for two computer interaction.
Figure 1. OSI networking model
How the signal is going from software on Computer A to Computer B is shown in Figure 1. The signal sent by software goes all the way down from Application layer to Physical layer before being sent to another workstation. Each of the layers of Computer A are adding a “message” to the transmitted data, that could be only read by the same layer on Computer B. More specifically, the “message” from Network layer can only be read by the Network layer, the “message” from Transport layer – by Transport layer, and so on. When data is being received from Computer A by Physical layer of Computer B, it is being forwarded up the OSI until it reaches Application layer. All this process is taking milliseconds to be done.
Note that OSI networking model is not perfect. It is not always essential to have “messages” from all the layers, also sometimes network services require use of multiple layers for one “message”.
More in details each Layer of OSI Networking Model is described in following posts:
