Application layer is considered to be an abstraction layer that specifies some of the interface methods and shared protocols used by communication network hosts. This is also used in both standardized computer networking models namely the Open System Interconnection or OSI model and the Internet Protocol Suite or the IP model. Despite the fact that these models are similar as far as their level layer is concerned, their detailed purposes and definitions are still completely different.
In IP model, the application layer is primarily consisted of interface methods and communication protocols which are thereby used in communication processes to the internet protocol computer networks. Their application layer can only standardize the communication. It will still depend on the underlying type of transport layer protocol. This will establish the host to be able to host information channel of transfer. This also helps manage some data exchange processes in a peer to peer or client-server networking model.
Despite the fact that IP mode doesn’t emphasize specified data formats or rules that application layer needs to consider during communication processes, its original specifications do not recommend or rely on the principle of robustness as far as the application design is concerned.
When it comes to the OSI model, application layer is even narrower in its scope. This defines application layer as an effective user interface. This is somehow responsible for the display of some received data and information to all users. In contrast with that, IP model is not concerned in such necessary details.
OSI also explicitly differentiates the additional functionality below the application layer and above the transport layers namely; the presentation layer and the session layer. OSI also emphasizes strict functional modular separation of these two layers. They also offer some protocol implementations in each of the different layer.
Layer 7 (The application)
Seven layers with respect to application layer can be separated into two different parts. Layers one to tree are considered to be the transportation set consisted of physical layer, network layer and data link layer. When it comes to the physical layer, this transmits raw bits over communication channels.
Now, the data link layer assures that the suitable physical protocols are assigned to the appropriate data. Network layers control subnet operations which are considered as identifiable network parts. These also decide just how the data will be sent to its recipient devices.
Transport layer which is also the forth application layer sustains the flow of the data. Recovery of data and error checking are also a part of that specific type of layer. This also accepts some data, split it into smaller units and ensures that all pieces of data arrived properly.
Layers five up to seven is considered to be the application layer set. Session layer allows users use different machines to be able to establish the best sessions between a user and a recipient. The presentation layer highlights semantics and syntax. This also converts the data sent at a standardized format.
The final layer is the application layer which contains different types of protocols. This is a layer that interfaces with all other types of applications and operating systems that communicate data between messages, files and other networking activities. Each application layer offers different functions that you must be aware of. This is also especially if you want to obtain a smooth flow of data in your system. More information can be found on Wikipedia here.