Network Model Illustration



Network Model :: Application Layer


The application layer in a network model enables the user, whether human or software, to access the network model. It provides user interfaces and support for services such as electronic mail, remote file access and transfer, shared database management, and other types of distributed information services.

Figure 2.14 shows the relationship of the application layer in a network model to the user and the presentation layer. Of the many application services available, the figure shows only three: X.400 (message-handling services), X.500 (directory services), and file transfer, access, and management (FTAM). The user in this example employs X.400 to send an e-mail message.

Application layer in a network model
Figure 2.14

Application layer in a network model

The application layer in a network model is responsible for providing services to the user.

Specific services provided by the application layer in a network model include the following:

Network virtual terminal.

A network virtual terminal is a software version of a physical terminal, and it allows a user to log on to a remote host. To do so, the application creates a software emulation of a terminal at the remote host. The user's computer talks to the software terminal which, in turn, talks to the host, and vice versa. The remote host believes it is communicating with one of its own terminals and allows the user to log on.

File transfer, access, and management.

This application allows a user to access files in a remotehost (to make changes or read data), to retrieve files from a remote computer for use in the local computer, and to manage or control files in a remote computer locally.

Mail services.

This application provides the basis for e-mail forwarding and storage.

Directory services.

This application provides distributed database sources and access for global information about various objects and services.

Summary of Network Model Layers

Summary of Network Model Layers
Figure 2.15

shows a summary of duties for each layer.



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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