Star and mesh topologies

A network's topology is the way its devices are connected to each other: its layout. The specification has two: star and mesh.

Choosing a topology is a trade-off between cost and reliability. The key question is: what happens if one connection, or one device, fails?

In a star topology, every device has its own connection to a central switch.

Advantages:

• If one cable or device fails, only that device is affected.
• It's fast and reliable: the switch sends data only to the device it's for, so there's less traffic.
• It's easy to add a new device: connect it to the switch.

Disadvantages:

• If the central switch fails, the whole network stops: it's a single point of failure.
• Every device needs its own cable to the switch, so a wired star can need a lot of cable.

Most school and office LANs are star networks.

In a mesh topology, devices are connected directly to each other. In a full mesh, every device connects to every other; in a partial mesh, some do. Data can take several routes to reach where it's going.

Advantages:

• If one connection or device fails, data takes another route: there's no single point of failure.
• Busy connections can be avoided by sending data a different way.

Disadvantages:

• A wired mesh needs a lot of cable, so it's expensive.
• It's harder to set up and maintain.

The internet's main routers are linked like a mesh. Wireless mesh networks, such as home mesh Wi-Fi systems, avoid the cabling cost.

Which would you choose?

• A small office on a budget: star. It's cheaper and easy to extend, and if one computer's cable fails, only that one is cut off.
• A hospital's network for patient monitors: mesh. It must keep working even if a link fails.