A topology is the physical layout of the cables and devices that connect the nodes of a network. The three basic topologies are bus, star, and ring. These topologies are so named because of the shape of the network they create. The less common type of physical topology is the mesh topology.
The bus network uses a single conduit to which all the network nodes and peripheral devices are attached. Each node is connected in series to a single cable.
At the cable's start and end points, a special device called a terminator is attached. A terminator stops the network signals so they do not bounce back down the cable.
The star network is the most common topology in use today. In a star network, a device called a hub is placed in the center of the network; that is, all nodes are connected to the central hub and communicate through it. Groups of data are routed through the hub and sent to all the attached nodes, thus eventually reaching their destinations. Some hubs known as intelligent hubs can monitor traffic and help prevent collisions. In a star topology, a broken connection (between a node and the hub) does not affect the rest of the network. If you lose the hub, however, all nodes connected to that hub are unable to communicate.
The ring topology connects the nodes of the network in a circular chain, with each node connected to the next. The final node in the chain connects to the first to complete the ring. With this methodology, each node examines data sent through the ring. If the data known as a token is not addressed to the node examining it, that node passes it along to the next node in the ring.
The mesh topology is the least used network topology and the most expensive to implement. In a mesh environment, a cable runs from every computer to every other computer. If you have four computers, you must have six cables – three coming from each computer to the other computers. The big advantage to this arrangement is that data can never fail to be delivered; if one connection goes down, there are other ways to route the data to its destination. The mesh topology is used for connecting routers on the Internet to make sure that data always gets through.