UK How star topology works
Star topology is a network layout in which each device has its own cable to one central device, and all traffic between devices passes through that centre. Drawn on paper it looks like a star or a hub with spokes, which is where the name comes from. A star network is the normal shape of a wired Ethernet LAN: every computer, camera and controller runs back to a switch.
Today the central device is an Ethernet switch. It learns which device sits on which port and forwards each frame only to the port that needs it, so every link runs at full speed in both directions. In older networks the centre was a hub, which repeated every frame to every port. Our comparison of a network hub vs a switch explains why hubs disappeared.
Star topology became the default when Ethernet moved from shared coax to twisted pair. The 10BASE-T standard in 1990 required a separate cable from each device to a central port, and every BASE-T Ethernet since has kept that shape.
Advantages and disadvantages of star topology
Its strengths and its main weakness both come from having one centre.
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Advantage: one fault, one device. A broken cable or failed device affects only its own link. Everything else keeps working.
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Advantage: easy to add and move devices. A new device needs one cable to a free port, with no break in anyone else’s connection.
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Advantage: easy to troubleshoot. Each port has its own link light, and a managed switch reports errors and traffic per port.
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Advantage: full speed per device. With a switch at the centre, each device gets its own full-duplex link.
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Disadvantage: a single point of failure. If the central switch or its power supply fails, every device connected to it loses the network.
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Disadvantage: more cable. Every device needs its own run back to the centre, which adds cable compared with a bus or ring along a line.
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Disadvantage: port count sets the size. A full switch means adding another switch, which turns the star into an extended star.
Star vs other topologies
The table compares a star with the other basic layouts on the points that usually decide the choice.
| Feature | Star | Bus | Ring | Mesh |
|---|---|---|---|---|
| Layout | All devices to one centre | All devices on one shared cable | Each device to two neighbours | Devices to several others |
| Effect of one cable fault | One device drops off | Whole segment can fail | Reroutes if protected | Reroutes |
| Single point of failure | The central switch | The backbone cable | None if protected | None |
| Cabling | One run per device | Least | Low along a line | Most |
| Typical use today | Office and cabinet LANs | Fieldbuses such as CAN and RS-485 | Industrial backbones | Network cores, wireless meshes |
Most real networks combine them, for example stars of devices around each switch, with the switches joined in a ring or a meshed core.
Extended star and tree layouts
An extended star joins several stars by linking their central switches to a higher-level switch. It is the normal layout of a building network: devices connect to access switches in each room or cabinet, and those switches connect to a core switch. A tree is the same idea drawn as a hierarchy.
The extended star keeps a star’s simplicity but adds more single points of failure, because losing an uplink cuts off a whole branch. Critical branches are usually given a second uplink, or their switches are joined in a ring, which needs managed switches to stop the extra links forming a loop.
Star networks in industrial systems
Inside a machine or control cabinet, the star is the natural layout: the PLC, HMI, drives and an edge computer each take one port on a DIN-rail switch. Unmanaged industrial switches suit a small star that needs no configuration, with wide-range DC input and wide operating temperatures.
Camera and sensor networks are stars too, often powered from the centre. Industrial PoE switches power each camera over its own cable. Copper twisted-pair links are limited to 100 m per run under IEEE 802.3, so longer spokes move to fibre. Our explainer on how twisted pair cable carries Ethernet covers the cable side, and our guide to choosing managed or unmanaged industrial switches helps decide which kind sits at the centre.
Setting up a star network
Start with a port count. List every device that needs a wired connection, add the uplink to the rest of the network and leave a few spare ports for later. Then decide whether any device needs power over the cable, and add up the PoE budget if so.
Place the switch where the cable runs to each device stay within 100 m, and label both ends of every cable with the port number, which makes faults quick to trace. Give the switch a reliable supply, because it is the one device every link depends on. Where downtime matters, a managed switch adds port monitoring and alarms, and a second power input removes one of the most common causes of a star going down.
Quick answers on star topology
Star topology: common questions
What is the central device in a star topology?
Usually an Ethernet switch. Older networks used hubs. In a home network the centre is the switch built into the router.
What happens if a cable breaks in a star topology?
Only that device loses its connection. The rest of the network carries on, which is one of the main reasons the star became the standard LAN layout.
What is an extended star topology?
Several stars joined together. Each group of devices connects to its own switch, and those switches connect to a central switch, forming a hierarchy.
Is star topology the most common?
Yes, for wired LANs. Every BASE-T Ethernet network is cabled as a star or extended star.
Can a star topology be wireless?
Yes. Devices connecting to one Wi-Fi access point form a logical star, with the access point at the centre.
We supply industrial and PoE switches sized to each installation and fit, cable and configure them with the computers and devices in every system we build.