Question

Give an example of possible information embedded in the header by the following layers:

1. Application layer.
2. Presentation layer
3. Session layer
4. Transport layer

Answer 1

Application Layer

Application layer interacts with an application program, which is the highest level of OSI model. The application layer is the OSI layer, which is closest to the end-user. It means OSI application layer allows users to interact with other software application.

Application layer interacts with software applications to implement a communicating component. The interpretation of data by the application program is always outside the scope of the OSI model.

Example of the application layer is an application such as file transfer, email, remote login, etc.

The function of the Application Layers are:

• Application-layer helps you to identify communication partners, determining resource availability, and synchronizing communication.
• It allows users to log on to a remote host
• This layer provides various e-mail services
• This application offers distributed database sources and access for global information about various objects and services.

Presentation Layer

Presentation layer allows you to define the form in which the data is to exchange between the two communicating entities. It also helps you to handles data compression and data encryption.

This layer transforms data into the form which is accepted by the application. It also formats and encrypts data which should be sent across all the networks. This layer is also known as a syntax layer.

The function of Presentation Layers:

• Character code translation from ASCII to EBCDIC.
• Data compression: Allows to reduce the number of bits that needs to be transmitted on the network.
• Data encryption: Helps you to encrypt data for security purposes — for example, password encryption.
• It provides a user interface and support for services like email and file transfer.

Session Layer

Session Layer controls the dialogues between computers. It helps you to establish starting and terminating the connections between the local and remote application.

This layer request for a logical connection which should be established on end user's requirement. This layer handles all the important log-on or password validation.

Session layer offers services like dialog discipline, which can be duplex or half-duplex. It is mostly implemented in application environments that use remote procedure calls.

Important function of Session Layer:

• It establishes, maintains, and ends a session.
• Session layer enables two systems to enter into a dialog
• It also allows a process to add a checkpoint to steam of data.

Transport Layer:

The transport layer builds on the network layer to provide data transport from a process on a source machine to a process on a destination machine. It is hosted using single or multiple networks, and also maintains the quality of service functions.

It determines how much data should be sent where and at what rate. This layer builds on the message which are received from the application layer. It helps ensure that data units are delivered error-free and in sequence.

Transport layer helps you to control the reliability of a link through flow control, error control, and segmentation or desegmentation.

The transport layer also offers an acknowledgment of the successful data transmission and sends the next data in case no errors occurred. TCP is the best-known example of the transport layer.

Important functions of Transport Layers:

• It divides the message received from the session layer into segments and numbers them to make a sequence.
• Transport layer makes sure that the message is delivered to the correct process on the destination machine.
• It also makes sure that the entire message arrives without any error else it should be retransmitted.