A network topology describes how devices are physically or logically arranged and connected in a network. OCR J277 requires knowledge of three topologies: star, mesh, and bus.
In a star topology, all devices connect to a central switch or hub. Data travels from a device to the central switch, which then forwards it to the destination device.
Star topology — all devices connected to a central switch
| Advantages | Disadvantages |
|---|---|
| Failure of one device does not affect others | If the central switch fails, the whole network fails |
| Easy to add new devices | More cable needed than bus topology |
| Easy to diagnose faults | Higher cost due to central switch |
| Good performance — dedicated connection to switch |
In a mesh topology, each device connects directly to some or all other devices. There are two types:
| Advantages | Disadvantages |
|---|---|
| Highly fault tolerant — data can take alternative routes if one path fails | Expensive — requires many cables |
| No single point of failure | Complex to set up and manage |
| Data can take the most efficient route | Many connections needed: n(n-1)/2 for full mesh |
| Good for critical infrastructure (internet backbone, military) |
The internet's backbone uses a mesh-like structure to ensure data can always find a route even if some links fail.
In a bus topology, all devices connect to a single shared cable (the "bus" or backbone). Data is sent along the cable and received by all devices, but only the intended recipient processes it.
Bus topology — all devices share a single backbone cable with terminators at each end
| Advantages | Disadvantages |
|---|---|
| Less cable required — cheap to install | Entire network fails if backbone cable breaks |
| Simple to set up — no central device needed | Performance degrades as more devices are added (all share one cable) |
| Difficult to diagnose faults | |
| Data collisions possible when two devices transmit simultaneously | |
| Less secure — all devices see all data |
Bus topology requires terminators at each end of the cable to prevent signal reflection.
| Feature | Star | Mesh | Bus |
|---|---|---|---|
| Single point of failure | Central switch | None (full mesh) | Backbone cable |
| Cable required | Medium | High (n(n-1)/2) | Low |
| Fault tolerance | Medium | High | Low |
| Ease of setup | Easy | Complex | Simple |
| Typical use | Schools, offices (LAN) | Internet backbone, military | Legacy/small networks |
8 questions · 21 marks
| Term | Definition |
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10 questions · 10 marks · 10 minutes