The Languages of the Internet
An internet (with a lower-case i) is simply an network of networks. But the
Internet (uppercase I) is the global internetwork that we all think of when
we hear about internetworking. This document explores mechanisms which make
interaction between computers on an internetwork possible.
The OSI model of networking
The International Standards Organization (ISO) has devised the Open Systems Interconnect
(OSI) network model.
The OSI model divides network functionality into seven layers. One may think
of each of these layers as being a separate software process or task, running on the
host machine. This organization allows each layer (or process) to communicate only
with its surrounding layers within a given host. Between hosts, each layer communicates
to its corresponding layer on the other machine, but only through the lower layers on
both machines.
This implies that several interfaces must be implemented at each layer - inter-layer interfaces
on a single host, and host to host communication of layers at the same level. For example,
the Transport layer must communicate with both the Session and Presentation layers within the
local host, as well as exchange data with the Session layers on remote hosts.
Discussion
It should be noted that the OSI reference model is only a guideline. An actual protocol
may or may not assume all responsibilities of one particular OSI layer. Indeed, a protocol
may also take on functions which span several layers. However, we may use the OSI model
to help us understand and classify the various functions that make up a particular implementation.
References.