2.6.Layer 5: The Session Layer

• The session layer, as shown in Figure below , is responsible for setting up, maintaining, and tearing down sessions.

• A session can be thought of as a conversation that needs to be treated separately from other sessions to avoid intermingling of data from different conversations.

1.Setting up a session:

• Examples of the procedures involved in setting up a session include :

  • Checking user credentials (for example, username and password)

  • Assigning numbers to a session’s communications flows to uniquely identify each flow

  • Negotiating services required during the session

  • Negotiating which device begins sending data

2.Maintaining a session:

• Examples of the procedures involved in maintaining a session include :

  • Transferring data

  • Reestablishing a disconnected session

  • Acknowledging receipt of data

3.Tearing down a session:

• A session can be disconnected based on mutual agreement of the devices in the session.

• Alternatively, a session might be torn down because one party disconnects (either intentionally or because of an error condition).

• In the event that one party disconnects, the other party can detect a loss of communication with that party and tear down its side of the session.