Presentation Layer

Shares information with the Application layer above it and the Session layer beneath it.

1. Converting information

Presentation Layer is a slightly confusing name, because this layer is not concerned with ‘presenting’ information to a person, but rather ‘presenting’ information to the various electronic devices in the correct format.

For example it will send video information in the right format to the graphics card \ monitor and the correct audio information to the sound card \ speakers.

It will take keyboard information coming down from the application layer and convert it into a format ready for the network.

So the main task of the presentation layer is to convert information into the correct format in both directions.

2. Keeping secrets

Another useful task for this layer is to be the ‘keeper of secrets’. The technical term is ‘encryption’. For example, say the Application layer is running a shopping application and you have just pressed the ‘Buy’ button. The job of the Presentation layer is to scramble the credit card number you have supplied so that only the store itself can read the number.

Note that the Presentation layer on the shop computer will be responsible for unscrambling the data back into the correct credit card number (decryption).

The presentation layer will scramble \ unscramble (encrypt \ decrypt) information if required.

3. Saving time and money.

Sometimes it is useful to only send the minimum amount of information into the network – bandwidth is expensive!

So the presentation layer will examine the information it needs to send through the network to see if it can be reduced (compressed) in some way. The technical term is ‘data compression’. There are many ways of doing this – for example ‘MP3’ for music files or ZIP files for other data.

When information streams in from the network, this layer has the task of uncompressing it if required..

The presentation layer may compress \ decompress information.