|Modern computer networks are designed in a
highly structured way. To reduce their design complexity, most
networks are organized as a series of layers, each one built
upon its predecessor.
The OSI Reference Model is based on a proposal developed by
the International Organization for Standardization (ISO). The
model is called ISO OSI (Open Systems Interconnection)
Reference Model because it deals with connecting open systems
- that is, systems that are open for communication with other
The OSI model has seven layers. The principles that were
applied to arrive at the seven layers are as follows:
- A layer should be created where a different level of
abstraction is needed.
- Each layer should perform a well defined function.
- The function of each layer should be chosen with an eye
toward defining internationally standardized protocols.
- The layer boundaries should be chosen to minimize the
information flow across the interfaces.
- The number of layers should be large enough that
distinct functions need not be thrown together in the same
layer out of necessity, and small enough that the
architecture does not become unwieldy.