A topology is the shape of a network: which device is connected to which. The shape decides how a packet travels from one host to another and what happens when something breaks. Then meet the boxes that make a LAN work, from the NIC to the router.
In a bus topology every device shares one backbone cable, so every packet reaches every device. In a star each device has its own cable to a central switch, which sends each packet only to its destination. In a mesh devices are linked to several others, so packets can take more than one route. A hybrid combines two or more topologies. A LAN is built from NICs/WNICs, cables, switches, WAPs, servers, bridges and repeaters; a router connects the LAN to other networks and forwards packets using IP addresses.
In the lab, choose a topology and click a computer, a cable or the switch to break it. The panel counts how many pairs of working computers can still communicate.
| Topology | Benefits | Drawbacks |
|---|---|---|
| Bus | little cable, cheap; easy to add a device | a break in the backbone stops the whole network; only one device can transmit at a time, so collisions increase and performance falls as devices are added; every device sees every packet, a security risk |
| Star | a broken cable affects only one device; the switch sends packets only to the destination, so fewer collisions and better security; easy to add devices | more cable than a bus; if the central switch fails, the whole network fails |
| Mesh | many routes, so no single point of failure; traffic can avoid busy or broken links | lots of cabling or links, expensive and complex to set up and manage |
| Hybrid | combines the strengths of each part, e.g. several stars joined by a backbone; easy to extend | complex to design and manage; a failure of a link joining the parts can split the network |
A mesh is not "every computer connected to every other" by definition; that is a full mesh. A partial mesh, like the internet's core, still gives several routes between nodes.
The syllabus asks how packets are transmitted between two hosts for a given topology. Describe the journey, not just the shape.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the lab, which part of a star network, if broken, stops every computer communicating?
In a bus topology, which devices receive a packet sent along the backbone?
What does a repeater do?
Which device connects a LAN to the internet and forwards packets using IP addresses?
Learn one clear sentence for what each device does. In the lab, click the router and the devices to see the addresses each uses.
| Device | Purpose |
|---|---|
| NIC (network interface card) | connects a device to a wired network; has a unique MAC address |
| WNIC (wireless NIC) | connects a device to a wireless network, using radio waves via an antenna |
| WAP (wireless access point) | lets wireless devices join a wired network; sends and receives radio signals |
| Switch | connects devices in a star; reads the destination MAC address and forwards the frame only to that device |
| Server | a computer that provides a service: file, print, email, web, authentication |
| Cables | copper (twisted pair, coaxial) or fibre-optic links between devices |
| Repeater | receives a weakened signal and regenerates (boosts) it, so a cable or wireless link can cover a longer distance |
| Bridge | joins two LAN segments that use the same protocol, so they act as one network; it only passes on frames meant for the other segment, which reduces traffic |
| Router | connects different networks, e.g. a LAN to the internet; forwards packets towards their destination using IP addresses |
Do not mix up a switch and a router. A switch works within one network and uses MAC addresses; a router works between networks and uses IP addresses.
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
Which is a drawback of a bus topology?
How does a switch decide where to send a frame?
Which hardware lets a laptop with a WNIC join a wired LAN?
Why is a mesh topology used for the core of the internet?
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