What are various design issues of session layer?

Design Issues of Session Layer:-  

The session layer is level five of the seven level OSI model. It responds to service requests from the presentation layer and issues service requests to the transport layer.

The session layer provides the mechanism for opening, closing and managing a session between end-user application processes, i.e. a semi-permanent dialogue. Communication sessions consist of requests and responses that occur between applications.

Session layers are commonly used in application environments that make use of remote procedure calls (RPCs).

An example of a session layer protocol X.225 or ISO 8327.

In case of a connection loss this protocol may try to recover the connection. If a connection is not used for a long period, the session layer protocol may close it and re-open it.

It provides for either full duplex or half-duplex operation and provides synchronization points in the stream of exchanged messages.

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List of Session layer services

• Authentication
• Permissions
• Session restoration (checkpointng and recovery) 

Authentication:

Authentication  is the act of establishing or confirming something (or someone) as authentic, that is, that claims made by or about the thing are true. This might involve confirming the identity of a person, the origins of an artifact, or assuring that a computer program is a trusted one.

Permissions or Access control

One familiar use of authentication and authorization is access control. A computer system supposed to be used only by those authorized must attempt to detect and exclude the unauthorized. Access to it is therefore usually controlled by insisting on an authentication procedure to establish with some established degree of confidence the identity of the user, thence granting those privileges as may be authorized to that identity.

In some cases, ease of access is balanced against the strictness of access checks. For example, the credit card network does not require a personal identification number, and small transactions usually do not even require a signature. The security of the system is maintained by limiting distribution of credit card numbers, and by the threat of punishment for fraud.

Checkpoints

Session layer is responsible for creating several checkpoints, checkpoints are also treated as recovery points i.e. in case of failure the system rollback to its previous checkpoint configuration or action.