OSI Model - Presentation Layer

Layer 2 - Presentation Layer

Presentation layer ensures that the data transmitted by the application layer of one system will be readable by the application layer on the another system. It gives the standard format for transmitting information across various systems, so that the data can be understood regardless of the type the system involved. The presentation layer is concerned with only the format and representation of the data but also with the data structure used by the programs.

The Presentation layer is concerned with the conversion of protocol such as encryption, decryption and graphic expansion of the application. It is also concerned with data compression, which can be used to reduce the size of the data packets. And cryptography, which is essential for privacy and authentication.

The Presentation Layer establishes context between Application Layer entities, in which the higher-layer entities may use different syntax and semantics if the presentation service provides a mapping between them. If a mapping is available, presentation service data units are encapsulated into session protocol data units, and passed down the stack.

This layer provides independence from data representation (e.g., encryption) by translating between application and network formats. The presentation layer transforms data into the form that the application accepts. This layer formats and encrypts data to be sent across a network. It is sometimes called the syntax layer.

Presentation layer provides

• Data Conversion : The sending device can converts text or data into general format (ASCII) for transmission over a network. The receiving computer converts this format (ASCII) to a format required by the destination applications.
• Data Encryption : Data is converted into encoded form, which can't be read by unauthorized persons
• Protocol Translation : Data is converted from one form to another and it is transmitted between dissimilar operating systems.

Some of the standard Graphical image formats are :- TIFF (Tagged Image File Format ) & JPEG ( Joint Photographic Expert Group )

Some of standard visual image representations are :- MIDI ( Musical Instrument Digital Interface ) used for digitized music. MPEG ( Moving Picture Experts Group )