Network Model Illustration



Network Model :: Session Layer


The services provided by the first three layers (physical, data link, and network layers in a network model) are not sufficient for some processes. The session layer in a network model is the network dialog controller. It establishes, maintains, and synchronizes the interaction among communicating systems.

The session layer in a network model is responsible for dialog control and synchronization.

Session layer in a network model
Figure 2.12

Session layer

Specific responsibilities of the session layer in a network model include the following:

Dialog control.

The session layer in a network model allows two systems to enter into a dialog. It allows the communication between two processes to take place in either half-duplex (one way at a time) or full-duplex (two ways at a time) mode.


The session layer in a network model allows a process to add checkpoints, or synchronization points, to a stream of data. For example, if a system is sending a file of 2000 pages, it is advisable to insert checkpoints after every 100 pages to ensure that each 100-page unit is received and acknowledged independently. In this case, if a crash happens during the transmission of page 523, the only pages that need to be resent after system recovery are pages 501 to 523. Pages previous to 501 need not be resent. Figure 2.12 illustrates the relationship of the session layer to the transport and presentation layers of a network model.



Network Model

Layered Tasks in a Network Model

Network Model: THE OSI MODEL

Network Model :: Physical Layer

Network Model :: Data Link Layer

Network Model :: Network Layer

Network Model :: Transport Layer

Network Model :: Session Layer

Network Model :: Presentation Layer

Network Model :: Application Layer

TCP/IP protocol suite in a Network Model

Addressing system in a Network Model

Important Points about Network Model

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