The presentation layer is mainly responsible  for the delivery of the information and formatting of information for the further processing of data display or manipulation purpose.

It relieves the application layer of concern regarding syntactical differences in data representation within the end-user systems.

The presentation layer is the lowest layer at which application programmers consider data structure and presentation, instead of simply sending data in the form of datagrams or packets between hosts.

Presentation Layer Functions

Here are some of the specific types of data handling issues that the presentation layer handles:

• Translation: . Networks can connect hetrogenous terminals together. Macintoshes, UNIX systems.The presentation layer handles the job of hiding the differences between machines.

• Compression:  Compression is done to improve the throughput of the data.
   
• Encryption: Some types of encryption  are performed at the presentation layer. This ensures the security of the data as it travels down the protocol stack.

The reason that the presentation layer is not always used in network communications is that the jobs mentioned above are simply not always needed. Compression and encryption are usually considered exceptional, and translation features are also only needed in certain circumstances.

Another reason why the presentation layer is sometimes not mentioned is that its functions may be performed as part of the application layer.