Introduction to Computer Network Topology

Are home networks star topology?

Five types of network topology, illustrated: Mesh, Ring, Star, Tree, Bus

Lifewire / Joshua Lees

In computer networking, topology refers to the layout of connected devices. This article introduces the standard topologies of networking.

Topology in Network Design

Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home network may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.

Network topologies are categorized into the following basic types:

  • Bus
  • Ring
  • Star
  • Tree
  • Mesh

More complex networks can be built as hybrids of two or more of these basic topologies.

Bus Topology

Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. The backbone is a single cable that functions as a shared communication medium that devices attach or tap into with an interface connector. A device that wants to communicate with another device on the network sends a broadcast message to the wire that the other devices see, but only the intended recipient can accept and process the message.

Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 (ThinNet) and 10Base-5 (ThickNet) were popular Ethernet cabling options for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems result. In addition, if the backbone cable fails, the network is unusable.

Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either clockwise or counterclockwise). A failure in any cable or device breaks the loop and can take down the network.

Ring networks are implemented using FDDI, SONET, or Token Ring technology. Ring topologies are found in office buildings and school campuses.

Star Topology

Many home networks use star topology. A star network features a central connection point called a hub node that is either a network hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable only takes down network access for one computer, not the entire LAN. If the hub fails, however, the entire network fails.

Tree Topology

A tree topology joins multiple star topologies together onto a bus. In its simplest form, only hub devices connect to the tree bus, and each hub functions as the root of a tree of devices. This bus/star hybrid approach supports future expansion of the network better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points).

Mesh Topology

Mesh topology introduces the concept of routes. Unlike the other topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (In a ring, although two cable paths exist, messages only travel in one direction.) Some WANs, most notably the internet, employ mesh routing.

A mesh network in which every device connects to every other is called a full mesh. Partial mesh networks also exist in which some devices connect only indirectly to others.

Summary

Topology remains an important part of network design theory. It's possible to build a home or small business computer network without understanding the difference between a bus design and a star design, but becoming familiar with the standard topologies provides a better understanding of networking concepts such as hubs, broadcasts, and routes.