Presentation layer is the sixth layer in the OSI reference model, which deals with the syntax (structure format) and semantics (meaning) of the data exchanged and how data is presented to the user.
Following are functions performed by the presentation layer :
Translation - As data types, formats and encoding methods are different for various operating systems, presentation layer translates it into common dependent format.
Compression - Reduces the size of data to be transferred and increases the throughput of the data.
Encryption and Decryption - Secret or confidential or important data is first encrypted using algorithm (protocol) and then transferred over the network. Decryption is done at the receiving end to get back the original form of data.