Networking - The OSI Seven-Layer Model - The Presentation Layer

The purpose of the Presentation layer is to make sure that information sent by one system can be understood by another system, even if the two use different internal representations. Where the lower layers are concerned with getting bits and frames and packets delivered, the Presentation layer is concerned with the meaning and format of the data.

In particular, the Presentation layer is responsible for:

Translating data between the formats used by applications and the common formats used on the wire,
Compressing data so that it can be transmitted more efficiently, and
Encrypting and decrypting data to provide confidentiality and, in some cases, integrity.

There are few, if any, hardware devices that operate purely at the Presentation layer. Instead, Presentation layer functions are usually built into software libraries, protocol stacks, and application frameworks. Some security appliances and accelerators, however, offload encryption and compression tasks that conceptually belong here.

The Presentation layer is responsible for several processes, each of which is responsible for a series of methods:

Data Representation and Translation
- Character set translation
  - Converting between different codes for text (for example, ASCII and EBCDIC),
  - Handling international character sets and encodings.
- Data structure representation
  - Agreeing on common formats for complex data (records, objects, and so on), and
  - Using description languages and tagging systems so that fields can be interpreted correctly.
Compression
- Reducing the number of bits required to represent information without changing its meaning (lossless compression), and
- In some applications, trading off a small loss of fidelity for much higher compression (lossy compression), as is common with audio and video.
Encryption and Security Services
- Encrypting data before it is passed to the lower layers so that only authorized parties can read it,
- Decrypting received data before it is handed to the Session or Application layers, and
- Supporting the use of digital certificates, keys, and message authentication codes to verify identity and integrity.

Let us move on to layer 7, the Introduction

Data Link (Layer 2)

Transport (Layer 4)

Presentation (Layer 6)

Conclusion