Done by: Mardonov B

SERVICE AND INTERFACE
Service-is a set of primitives that
the level grants the level above it.
The service determines which operations a given
the level is intended to be completed on behalf of
its users, but it doesn't say anything about
how these operations are implemented.
Service refers tointerfacebetween
levels.
The lower layer is the service provider,
and the overlying one is the service user.
A certain set of functions performed by a given layer for a higher layer, as well as the formats of messages exchanged between two neighboring layers during their interaction, is called interface
DEFINITION of model OSI
Seven-layer OSI Model - description form informational
system, its structures included in its components, as well as
rules and procedures interaction of elements of information
systems in work process
THE BASIS OF THE BASIC REFERENCE MODEL
Four basic elements:

• open systems;
• objects (activities) of the level;
• connections that connect objects and allow them to exchange information;
• physical means of connection.

Application process due to the existence of functions of seven
levels receives a variety of services. Along with the,
level organization provides relative
subsystem independence
THE BASIS OF THE BASIC REFERENCE MODEL
ISO documents for each level
determine:

• level assignment;
• the service provided by this layer to the layer above it;
• functions performed by the layer
• service received from the underlying layer.

The application layer provides access to application processes
users to the resources and service of the information system (network).
These may include programs that:

• receiving or sending files
• network management
• database access
• transmission of mail

The main task of this level is to provide a convenient interface for
user.
Examples of application layer protocols:NCP- protocols
kernels in the OSNovell NetWare,SMB MS Windows NT, FTPand
TFTP(StackTCP/IP), X.400, NFS (UNIX).
On this unit of data is considered asMessage(message).