Session Layer of OSI Model - MetaTutorials

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Session Layer of OSI Model

In this networking article, you will learn about the session layer of the OSI reference model in detail with its diagram and functions. We will also discuss the protocols used by the session layer. 

What is the Session layer of OSI model?

The Session layer of the OSI model is the fifth layer from the bottom which is responsible for establishing, controlling, and terminating the dialogs (connections) between the end-user local and remote applications.
It controls one or more than one connection for each application and directly interacts with the presentation layer as well as the transport layer. This layer uses all the services provided by the transport layer for maintaining and synchronizing sessions. 
It implements the sessions on web browsers using AppleTalk Protocol, Session Control Protocol, and Zone Information Protocol. The session layer also synchronizes the information from the different sources. 
The various protocols of this layer manage the session restoration through checkpoint and recovery. 
Now, we will discuss the functions of the session layer.

Functions of Session layer 

Following are the important functions of the session layer which help in establishing, maintaining, and terminating the connection between two remote and local applications:

1. Dialog (Connection) control: This layer acts as the dialog controller in the OSI model which lets the systems interact either in half-duplex or full-duplex mode for the data transmission.  

2. Synchronization: The session layer lets the processes add the checkpoints into the stream of data. The checkpoints are referred to as the synchronization points in the communication of data over the network. 
This feature is beneficial when the data is lost due to crash and damage. If the checkpoints have been added to the stream of data, then there will be no need to transmit the data again from the beginning. 

3. Token Management: Token Management is also another responsibility of the session layer, through which this layer prevents two end-users from accessing the same critical operation at one time.

Protocols of Session layer 

Following are some protocols used in the session layer for safe and secure communication between two end-user local and remote applications:
1. ADSP
2. ASP
3. PAP
4. PPTP
5. RPCP
6. RTCP
7. SCP

ADSP (AppleTalk Data Stream Protocol)

ADSP was developed by Apple Inc in 1985. It is a connection-oriented protocol which transfers the stream of data in the full-duplex mode through the AppleTalk internet. 
In the session layer, it establishes the connection for data transmission between multiple networking devices. 

ASP (AppleTalk Session Protocol)

AppleTalk Session Protocol in the session layer allows more than one ASP workstation to set up a connection with the same server simultaneously. 

PAP (Password Authentication Protocol)

Password Authentication Protocol is used by the PPP (Point-to-Point Protocol) links for validation. This protocol is compatible with almost all network operating systems and remote servers. 

PPTP (Point-to-Point Tunneling Protocol)

PPTP is also another protocol which was created in the 1990s for establishing the connection with virtual private networks. This protocol enhances the own VPN over the public network through tunnels. 
It is fast and easy to establish because it does not require any special software to use.

RPCP (Remote Procedure Call Protocol)

RPCP is basically a type of client-server communication. In this protocol, one computer requests a service from another computer on the network without having the network's information.

RTCP (Real-Time Transport Control Protocol)

RTCP is a protocol of session layer which performs its functionality with the real-time protocol for monitoring the data transmission for large multi-cast networks. 

SCP (Session Control Protocol)

Session Control Protocol is a simple protocol which establishes the multiple light-duty connections over a single TCP (Transmission Control Protocol) connection.