This layer is responsible for opening and closing the communication, also called sessions.
The session layer ensures sessions stay open long enough to transfer all communicated data.
It also uses checkpoints, this ensures that a file download can be resumed even if the connection is lost halfway through.

The session layer helps to setup and manage connections. It enables the sending and receiving and data which is followed by the terminations of sessions. The session layers has helpers which are called API’s (Application Programmer Interfaces). Such an example is NETBIOS (Network Basic Input Output Systems). It enables applications on different devices to communicate with each other.

Just before a connection is established the server performs an authentication function. This is a process to verify who you are. Such as username and password, if these match, a session is established between your device and the receiving device. After the authentication, the authorisation is checked. Authorisation is the process used by the server to identify if you have the right permissions to access information.

Both these functions, authentication and authorisation, are performed by the session layer.
The session layer keeps track of the files that are being downloaded. For example, if a web server contains images these are stored as separate files on the server. When a request to these images is made the web browser opens a separate session to the server to download such files separately. These files are received as data packets. The session layer keeps track of what packet belongs to what file. It also tracks where this packet is supposed to go, e.g. the browser. So, the session layer helps in session management, authentication and authorization.

The web browser performs all functions of the application, presentation and session layer!

List of protocols running in the presentation layer:

  • ZIP
  • RPC
  • PAP
  • RPC
  • SCP
  • SDP

Exam Question

Explain the working of Synchronisation within the Session Layer

The session layer implements checkpoints . These are considered synchronisation points into the stream of data. For example, if a server is sending a large file (1000 pages) it is beneficial to have checkpoints at an X amount of pages. This ensures that if a crash happens during the transmission there is no need to start the process from scratch again.

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