2.1 Networking Terminology  
  2.1.4 Network topology  
Network topology defines the structure of the network. One part of the topology definition is the physical topology, which is the actual layout of the wire or media. The other part is the logical topology, which defines how the media is accessed by the hosts for sending data. The physical topologies that are commonly used are as follows:
  • A bus topology uses a single backbone cable that is terminated at both ends. All the hosts connect directly to this backbone.
  • A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable.
  • A star topology connects all cables to a central point of concentration.  
  • An extended star topology links individual stars together by connecting the hubs and/or switches. This topology can extend the scope and coverage of the network.
  • A hierarchical topology is similar to an extended star. However, instead of linking the hubs and/or switches together, the system is linked to a computer that controls the traffic on the topology.
  • A mesh topology is implemented to provide as much protection as possible from interruption of service. The use of a mesh topology in the networked control systems of a nuclear power plant would be an excellent example. As seen in the graphic, each host has its own connections to all other hosts. Although the Internet has multiple paths to any one location, it does not adopt the full mesh topology.

The logical topology of a network is how the hosts communicate across the medium. The two most common types of logical topologies are broadcast and token passing.

Broadcast topology simply means that each host sends its data to all other hosts on the network medium. There is no order that the stations must follow to use the network. It is first come, first serve. Ethernet works this way as will be explained later in the course.

The second logical topology is token passing. Token passing controls network access by passing an electronic token sequentially to each host. When a host receives the token, that host can send data on the network. If the host has no data to send, it passes the token to the next host and the process repeats itself. Two examples of networks that use token passing are Token Ring and Fiber Distributed Data Interface (FDDI). A variation of Token Ring and FDDI is Arcnet. Arcnet is token passing on a bus topology.

The diagram in Figure shows many different topologies connected by network devices. It shows a network of moderate complexity that is typical of a school or a small business. It has many symbols, and it depicts many networking concepts that will take time to learn.   

 

Web Links

Network Topologies

http://www.icoe.k12.ca.us/support/ network/topology.htm