A Guide to the Presentation Layer | OSI Model Layer 6

Understanding the layers of the Open Systems Interconnect (OSI) model can help users conceptualize data communication over a network. Layer 6 in the OSI model - the presentation layer - translates, compresses, and encrypts data across networks. In this article, we’ll explain what the presentation layer is, how it works, and its functions and protocols.

What is the presentation layer?

The presentation layer is the sixth layer in the OSI model. Known as a translator, it converts data into an accurate, well-defined, standard format after it receives it from the application layer.

The converted format varies, however, based on the type of data received. Some formats include:

  • EBCDIC (Extended Binary-Coded Decimal Interchange Code) and ASCII (American Standard Code for Information Interchange) for text files
  • MIDI, JPG, and QuickTime for audio files
  • GIF, JPEG, and TIFF for image files
  • MPEG, MOV, and AVI for movie files

The data from the application layer is changed into its proper form and then transmitted to other layers. If not for the presentation layer, the data would be sent as datagrams or data packets between hosts. This layer ensures a successful file transfer.

In computer networking, the OSI model layer 6 is sometimes referred to as the syntax layer because it maintains the proper syntax of transferred data. This layer also deals with the semantics of information transmitted over the network.

The presentation layer is the sixth layer in the OSI model.

Functions of the presentation layer

As the sixth layer in the OSI model, the presentation layer is thus responsible for three general functions: translation, compression, and encryption and decryption.

Translation

Layer 6 translates data based on the host’s needs. Different hosts represent data differently, especially when dealing with heterogeneous networks.

The data received from the application layer usually includes numbers and characters. The presentation layer then translates the data into a transportable and storable format that the receiving application can understand.

On the sender's end, the layer prepares data in the most common binary format. This subsequently benefits the recipient by ensuring proper structure and format of the data.

Compression

Data compression reduces data size by encoding the actual number of bits that require transmission on the network. Therefore, it helps speed up file transfer, save storage capacity, reduce bandwidth, and decrease storage hardware costs.

Compression in the presentation layer aims to reduce the number of bits needed to represent data; the aforementioned encoding can thus be achieved by inserting a single repeat character or removing all unneeded characters.

The process helps accelerate the rate at which data transmits to other layers. If you’re sending many files, the layer ensures that the files reach its destination quickly and without quality loss.

Encryption and decryption

Both encryption and decryption occur at the sixth layer. Encryption converts data from a readable format, plaintext, into an unreadable format, ciphertext. However, only the user with the correct encryption key can access the data. The correct key then decrypts the data for proper display on the next layer.

Encryption occurs at the transmitter, and decryption occurs at the receiver. Both tasks are crucial to data security. Encryption and decryption protect data, protect against file tampering, and increase trust.

Other functions of the presentation layer

In addition to the primary functions above, the presentation layer also allows and manages high-level data structures like banking records. It solves string representation issues, deals with the semantics and syntax of messages, performs character translation functions, and serializes by translating data into an easily-stored format.

Presentation layer protocols

To perform the necessary functions, the presentation layer utilizes certain protocols, including:

  • AFP (Apple Filing Protocol). AFP, a communication protocol designed for Mac-based platforms, specifically offers services to MacOS. The protocol allows computer users to share files easily over a network.
  • SSL (Secure Socket Layer). SSL is an Internet security protocol that safeguards sensitive data transferred between web browsers and servers. Its sole purpose is to encrypt Internet connections and link between web clients and servers. It ensures that data passing through the OSI model remains private.
  • NCP (NetWare Core Protocol). NCP is a network protocol designed for accessing files, messaging, printing, creating directories, synchronizing clocks, and executing remote commands, as well as other network service functions.
  • XDR (External Data Representation). XDR is the standard for encoding and decoding data. It allows data to transfer between systems.
  • NDR (Network Data Representation). NDR provides several types of data representation and various constructed data types. Therefore, it plays a vital role in implementing the presentation layer.

Who needs to understand the presentation layer?

Understanding the OSI model is essential for IT industry professionals. The model acts as a reference guide in developing communication products and software applications.

Understanding the presentation layer benefits network administrators who must troubleshoot network issues and software vendors who program software. It helps vendors create interoperable products.

Furthermore, understanding the sixth layer benefits cybersecurity professionals, as the presentation layer takes care of data encryption. Some common threats at this level include encoding attacks, encryption attacks, and decryption downgrade attacks. Therefore, professionals use the presentation layer to secure data transmitted over a network.

Frequently asked questions

Which three main functions are performed by the presentation layer?

The layer’s three main functions are data translation, data compression, and data encryption and decryption. Therefore, in this way, data becomes secure and compatible.

What is the primary purpose of the presentation layer?

Though it has many purposes, its main purpose is to translate data into an acceptable format that computer systems can understand.       

What technologies are used in the presentation layer?

The technologies used in the presentation layer are JavaScript, HTML, CSS, and jQuery.

What are the other layers in the OSI model?

Though an important layer, the presentation layer isn't the only layer in the OSI model. The other layers in the OSI model include the physical layer, the data link layer, the network layer, the transport layer, the session layer, and the application layer.