Layer 7: The Application Layer

The Application layer of the OSI model supports these services:

File services  Store, move, control access to, and retrieve files

Print services  Send data to local or networked printers

Message services  Transfer text, graphics, audio, and video over a network

Application services  Process applications locally or through distributed processing

Database services  Use the local computer to access a network server for database storage and retrieval functions.

Note 

Applications such as Microsoft Word and Excel do not directly interface with the Application layer of the OSI model. However, the Application layer provides those applications with underlying services, such as file and print services.

In addition, the Application layer of the OSI model advertises any services that are being offered and determines whether requests made by the client should be serviced locally or remotely.

Service Advertisement

Service advertisement means that the computer is making its resources available over the network. For example, any Windows XP/.NET Server computer running the server service automatically advertises any file or print resources that it is sharing.

Service Processing

Service processing determines whether a request should be processed locally or remotely.

Assume, as an example, that you have two computers: computer A and computer B. If computer A makes a request to its local hard drive, the I/O manager (which handles all input and output) will direct the request to be handled locally. If the computer makes a network request-in this case, computer A is using the drive letter F to represent a shared folder on computer B-the I/O manager will process the request and redirect it to the network.

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Note 

At the Application layer of the OSI model, data is referred to as a message or simply data.




MCSA. MCSE 2003 JumpStart. Computer and Network Basics
MCSA/MCSE 2003 JumpStart
ISBN: 078214277X
EAN: 2147483647
Year: 2003
Pages: 203
Authors: Lisa Donald

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