What is the Session Layer?

The Open System Interconnect (OSI) model in computer networking has seven layers, each of which is assigned a set of functions. Layer 5, or the session layer, is essential in initiating requests and responses of dialogue within systems. The model helps establish, manage, and terminate communication. Learn what the OSI session layer is, its primary functions and protocols, and how it fits into the OSI model.

What is the Session Layer?

In the Open Systems Interconnection (OSI) model, the session layer is the fifth layer, which controls the connections between multiple computers. The session layer tracks the dialogs between computers, which are also called sessions. This layer establishes, controls, and ends the sessions between local and remote applications.

How does it work?

The session layer relays information between the presentation layer and the transport layer, so it needs a stable connection. It must do the following things to establish and maintain a connection between entities:

• Map the session address to the shipping address
• Select Quality of Service (QoS) parameters
• Handle negotiations between session parameters
• Transmit limited transparent user data
• Monitor the data transfer phase

Functions of the Session Layer

• Session Establishment: It establishes connections between devices which is known as sessions. The session which is created allows users to share data, remote access, and file management. When the session is released, the transport connection is mapped. The ways in which transport connection maps are one-to-many, one-to-one, and many-to-one.
• Data Transfer: It is the very basic function of the session layer, which handles the exchange of data between systems in a full-duplex or half-duplex mode of transmission. The session layer allows only one user to transmit data in half-duplex as well as exchange data in full-duplex mode.
• Dialog Management: The session layer keeps log data on which connections are established to transmit and receive data, which is called dialog management. It is accountable for establishing, synchronizing, preserving, and ending the conversation between the sender and the receiver. It uses a token mechanism in which the user sharing the data is given a token in case of half duplex mode and, after the exchange, transfers it to another device. The token method maintains the efficiency of the connection.
• Synchronization: The session maintains proper connectivity between systems, and if any error occurs, then it provides a recovery option which is called a known state. The session layer adds synchronization bits to the message to use the known state in the event of an error. These bits can be used as checkpoints. It adds synchronization points or checkpoints to the data stream for longer communication. It ensures that the data streams are successfully received and acknowledged up to the checkpoints. In case of any failure, only the stream needs to be retransmitted after the checkpoints.
• Authentication: The process of identification is known as authentication. It takes a guarantee from the user to permit them access to the data. Authentication is very important because it provides security.
• Authorization: It grants privileges after authentication of the user. Authorization means providing access to the data that is authorized to the specific user.

Session layer protocols

There are several different protocols, including the following:

• AppleTalk Data Stream Protocol (ADSP) and AppleTalk Session Protocol (ASP) (Deprecated).
• H.245.
• ITU X.225.
• Layer 2 Forwarding (L2F) and Layer 2 Tunneling Protocol (L2TP).
• Network Basic Input/Output System (NetBIOS).
• Point-to-Point Tunneling Protocol (PPTP).
• Real-time Transport Control Protocol (RTCP).
• Remote Procedure Call (RPC).
• Session Control Protocol (SCP).
• SIP
• SOCKS Proxy.

Conclusion

In this article, you have gained knowledge of the session layer in the OSI model. It is the fifth layer of the OSI model. The work of this layer is to open, maintain, and end the session for safe and secure communication. You have studied the various functions of the session layer in the OSI model, such as session establishment, dialog management, data transfer, synchronization, authentication, and authorization.