Notes on Presentation Layer

The Sixth layer of the OSI model is the presentation layer. The presentation layer controls two aspects of the data exchange between the communicating systems, and those two aspects are syntax and semantics. Data is to be converted into syntax and semantics.

Syntax And Semantics

So, what are syntax and semantics? Data is converted into syntax and semantics. The syntax is the structuring or arrangement of the data or information arranged in an ordered way. Next is semantics; semantics is referred to as adding logical meaning to the data or information. This gives the functions of the presentation layer: 

1. i) First is translation; it is an important function as many device node systems are manufactured with different functions, and they have different operating systems. For example, a device with an operating system has to communicate with a device with an operating system; or a device with an upgraded operating system and upgraded features have to communicate with a device with the old technology. In that case, the data translator for the network comes into play which is done by the presentation layer. It allows different devices with different features, operating systems, application features or upgraded features to communicate with one another. It allows interoperability of the various computer systems. So what happens is that in the process of data exchange, be it anything numbers, alphabets, image, audio and video process application. The presentation layer at the sender side, the device in which data translator for the network or information, the presentation layer at the sender side converts that data from the sender supported format, the format in which it is supported in the sender’s device, into a common format.
2. ii) Next feature is encryption and decryption. For encryption and decryption, data is formed at this stage. It generally involves converting simple data into a coded form to maintain secrecy. So this is generally done when sharing sensitive, confidential information over the Internet. The encryption-decryption process is used, so encryption converts the simple data into a coded form, and decryption performs the reverse process, that is, it converts the code into the original data. Here another concept that is used is the code that is used as this cypher. You understand that the presentation layer performs encryption and decryption, converting simple data into the coded form and again coded data into a simple original form for the next task.

The presentation layer performs compression. Compression generally is used to reduce the size of the data for easier transmission without exploiting a large portion of the transmission. The bandwidth of the channel is done by reducing the number of bits in the data without compromising the quality of the data, and that is called data compression. This is the process of encryption and decryption; the sender’s device converts the original data into the coded form using a cypher, and again at the receiver side, the coded data is again converted into original data through this process.

The data packet structure in the presentation layer, as usual, consists of two portions: first is the header portion, which is used for identification of the sender and receivers address, and it stands for header 6 because it is the sixth layer of the OSI model. These are the data bits of the data which is to be transmitted, so again there are arrowheads in both directions because the data transmission and reception innovation model is bi-directional both from sender to receiver and from receiver to sender.

Conclusion

There’s more than just one layer in the iOS model, so if you have an interest in this mechanism, do make sure to learn of them as well.