Definition of a network : A network is a wide variety of systems interconnected components. A computer network is a system for communication among two or more computers. These networks may be fixed (cabled, permanent) or temporary (as via modems).
OSI stands for Open System Interconnection, an ISO standard for worldwide communications that defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
At one time, most vendors agreed to support OSI in one form or another, but OSI was too loosely defined and proprietary standards were too entrenched. Except for the OSI-compliant X.400 and X.500 e-mail and directory standards, which are widely used, what was once thought to become the universal communications standard now serves as the teaching model for all other protocols.
Most of the functionality in the OSI model exists in all communications systems, although two or three OSI layers may be incorporated into one.
OSI is also referred to as the OSI Reference Model or just the OSI Model.
Click on the link to get more informations about this subject:
A network topology is the pattern of links connecting pairs of nodes of a network. A given node has one or more links to others, and the links can appear in a variety of different shapes. The simplest connection is a one-way link between two devices. A second return link can be added for two-way communication. Modern communications cables usually include more than one wire in order to facilitate this, although very simple bus-based networks have two-way communication on a single wire.
Network topology is determined only by the configuration of connections between nodes; it is therefore a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types are not a matter of network topology, although they may be affected by it in an actual physical network.
Commonly use with 10baseT technology, the bus topology is most of the time used in industry for linking their machine together. (deprecate)
The ring topology is a widely used for “token ring” network and FDDI. It provide security in case one of the computer is offline using 2 differents route directions.