The shape of the lesson
By the end of the lesson, learners can
- Four topologies: In the lab, choose a topology and click a computer, a cable or the switch to break it.
- Packets between two hosts: The syllabus asks how packets are transmitted between two hosts for a given topology.
- LAN hardware: Learn one clear sentence for what each device does.
- Bus: every device sees every packet; one backbone, terminators, one break stops all.
- Star: switch forwards only to the destination; the switch is the single point of failure.
- Mesh: many routes, no single point of failure, expensive.
- Switch vs router: MAC within a network vs IP between networks.
One picture every idea returns to
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.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, How the wires run.. A topology is the shape of a network: which device is connected to which. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Four topologies | In the lab, choose a topology and click a computer, a cable or the switch to break it. Project tab 6 of the lab (Topologies: break a link) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Packets between two hosts | The syllabus asks how packets are transmitted between two hosts for a given topology. Model the worked example Justify a topology on the board, one line at a time. Your turn: A small office wants a cheap network that is easy to extend and where one faulty cable will not stop everyone working. Bus or star? | Pairs |
| 21 to 30 min | Teach and check: LAN hardware | Learn one clear sentence for what each device does. Project tab 3 of the lab (Router, NIC and addresses) and let a student drive it while the class predicts. | Corners |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 22 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in LAN hardware, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| 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. |
| 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. |
Network topologies and hardware: worksheet
6 questions, 22 marks. Written in the style of the papers; no past paper question is reproduced.
Describe how a packet is transmitted from host A to host D in a star topology.
Describe how a packet is transmitted between two hosts on a bus network.
A college is building a network across three buildings. Each building has its own switch with 30 computers. Name a suitable topology and justify your choice.
State the purpose of each device: (a) WNIC (b) bridge (c) repeater (d) wireless access point.
Describe the role and function of a router in a network.
Compare a switch and a router.
Answer key and marking notes
- Host A sends the packet along its own cable to the central switch.
- The switch reads the destination (MAC) address in the packet/frame.
- The switch looks up which port host D is connected to.
- The switch forwards the packet only along the cable to host D (no other host receives it).
- The sending host checks the backbone is free and transmits the packet onto it.
- The signal travels along the whole backbone and reaches every device.
- Each device checks the destination address; only the addressed host accepts it, and terminators absorb the signal at the ends.
- Hybrid topology.
- Each building is a star: a broken cable affects only one computer, and the switch sends packets only to the destination.
- The three switches are joined by a backbone (or mesh of links) between the buildings.
- It is easy to extend, and buildings can be added without redesigning the whole network.
- (a) Allows a device to connect to a wireless network (sends and receives radio signals).
- (b) Connects two LAN segments using the same protocol so they act as one network.
- (c) Regenerates/boosts a signal so it can travel a longer distance.
- (d) Lets wireless devices connect to a wired network.
- Connects different networks together, e.g. a LAN to the internet / a WAN.
- Receives packets and reads the destination IP address.
- Uses a routing table to decide the next hop / best route and forwards the packet.
- Translates between private and public IP addresses (NAT) / may assign IP addresses using DHCP.
- A switch connects devices within one network (LAN); a router connects different networks.
- A switch uses MAC addresses to forward frames; a router uses IP addresses to forward packets.
- A router chooses a route between networks (routing table); a switch forwards only to the device on the correct port.
6 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
In a star network, what does the central switch do with a frame sent from one computer to another?
- AIt reads the destination MAC address and forwards the frame only to that computer
- BIt sends the frame to every computer, and each one checks whether it is the destination
- CIt reads the destination IP address and sends the frame on to the internet
- DIt stores the frame until the destination computer asks the switch for it
In which network does a single faulty component stop every device communicating?
- AA star network whose central switch fails
- BA star network in which one computer's cable is cut
- CA full mesh network in which one link is cut
- DA bus network in which one computer is switched off
What is the purpose of a bridge?
- ATo join two LAN segments that use the same protocol so they act as one network
- BTo connect a LAN to the internet and route packets using IP addresses
- CTo regenerate a weakened signal so that it can travel further
- DTo let devices with wireless network cards join a wired network
Which statement correctly compares a router with a switch?
- AA router forwards packets between networks using IP addresses; a switch forwards frames within one network using MAC addresses
- BA router forwards frames within one network using MAC addresses; a switch forwards packets between networks using IP addresses
- CA router and a switch both send every packet to all connected devices, but a router is faster
- DA router is needed only for wireless devices; a switch is needed only for wired devices
A company keeps adding computers to its bus network, and the network becomes noticeably slower. What is the main reason?
- AOnly one device can transmit on the shared backbone at a time, so more devices cause more collisions and waiting
- BEach new computer needs its own cable to a central switch, which overloads the switch
- CThe terminators absorb more of the signal as more computers are attached
- DEach packet must now be copied by every computer and sent on to the next one
A hybrid network has two star segments. Switch A serves the PCs in building 1 and switch B serves the PCs in building 2; the two switches are joined by a backbone cable. Which route does a packet take from PC1 in building 1 to PC9 in building 2?
- APC1 to switch A, along the backbone to switch B, then only to PC9
- BPC1 directly along the backbone to PC9, missing out both switches
- CPC1 to switch A, along the backbone to switch B, then to every PC in building 2
- DPC1 to switch A, which sends it to every PC in both buildings
Quiz key
A switch looks up the destination MAC address in its table and sends the frame only down that port, which cuts collisions and improves security. Sending to every device is what happens on a bus (or with an old hub). Using IP addresses to forward between networks is a router's job. A switch forwards frames straight away; it does not hold them waiting for a request.
Every packet in a star passes through the central switch, so its failure stops the whole network. A cut cable in a star isolates only the computer on that cable. A mesh has other routes round a cut link. On a bus, a switched-off computer simply stops reading the backbone; the others carry on (it is a break in the backbone itself that stops a bus).
A bridge joins two segments of a LAN that use the same protocol and passes on only frames meant for the other segment, which reduces traffic. Connecting to the internet using IP addresses is a router. Regenerating a signal is a repeater. Letting wireless devices join a wired LAN is a wireless access point.
A router reads the destination IP address and uses its routing table to send packets towards another network; a switch works inside a LAN, forwarding frames to the port with the matching MAC address. The second option swaps the two roles. Neither device broadcasts every packet to every device. Both handle wired traffic; wireless devices join through a WAP.
On a bus every device shares the backbone, so only one can transmit at a time; with more devices there are more collisions and more time spent waiting, so performance falls. A central switch belongs to a star, not a bus. Terminators simply stop the signal reflecting at the ends; their effect does not grow with the number of devices. Devices on a bus read the signal as it passes; they do not copy and resend each packet.
In a hybrid the packet follows each part's rules: star to switch A, the backbone to switch B, then star again, where switch B forwards it only to PC9's port. PCs in a star are not attached to the backbone directly, so the packet cannot skip the switches. A switch forwards to the destination port only, so it does not send the packet to every PC in a building, let alone in both.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.