The shape of the lesson
By the end of the lesson, learners can
- Serial or parallel: Send the same byte both ways in the lab.
- Which direction?: Switch the lab between simplex, half-duplex and full-duplex and send data from each end.
- Pick the method: A full answer names two things: serial or parallel, and simplex, half-duplex or full-duplex, each with a reason linked to the scenario.
- Serial: one bit at a time, one wire, long distances, no skew.
- Parallel: several bits at once, several wires, fast but short distances only (skew).
- Direction: simplex one way; half-duplex both ways in turn; full-duplex both ways at once.
- Scenario questions: name both parts and link each reason to the scenario.
One picture every idea returns to
Every connection is described in two ways. How many bits at once: serial sends one bit at a time down a single wire; parallel sends several bits at the same time down several wires. Which direction: simplex is one direction only; half-duplex is both directions but only one at a time; full-duplex is both directions at the same time. Parallel is faster over short distances but suffers skew (bits arriving at different times) over long ones, so serial is used for long distances.
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, One wire or many?. Data can travel one bit at a time down a single wire, or several bits at once down several wires. 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: Serial or parallel | Send the same byte both ways in the lab. Project tab 2 of the lab (Serial and parallel transmission) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Which direction? | Switch the lab between simplex, half-duplex and full-duplex and send data from each end. Project tab 2 of the lab (Simplex, half-duplex and full-duplex) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Pick the method | A full answer names two things: serial or parallel, and simplex, half-duplex or full-duplex, each with a reason linked to the scenario. Model the worked example Video call on the board, one line at a time. Your turn: A weather sensor on a mountain sends temperature readings 2 km down a cable to a computer, which never sends anything back. Which method? | 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, 16 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 Pick the method, 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 |
|---|---|
| "Parallel is faster" is only true over short distances. | If a question involves a long cable, the answer is serial, and the reason is skew. |
| Do not just name the method. | A justification such as "because data only needs to travel in one direction" is what earns the second mark. |
Serial and parallel, simplex, half-duplex and full-duplex: worksheet
6 questions, 16 marks. Written in the style of the papers; no past paper question is reproduced.
Describe how data is transmitted using parallel data transmission.
Give one advantage and two disadvantages of parallel transmission compared with serial transmission.
Describe the difference between simplex, half-duplex and full-duplex data transmission.
A school sends files from a server to a printer 80 metres away. The printer sends status messages back, such as "out of paper", but never while it is receiving a file. Identify the most suitable transmission method and justify your choice.
Explain why full-duplex transmission is used for an online multiplayer game.
A student says: "Parallel transmission is always better because it is faster." Evaluate this statement.
Answer key and marking notes
- Several bits are sent at the same time.
- Using several wires (one wire per bit).
- Advantage: faster over short distances because several bits are sent at once.
- Disadvantage: data can be skewed (bits arrive at different times) over long distances.
- Disadvantage: needs more wires so is more expensive; wires can interfere with each other.
- Simplex: data is sent in one direction only.
- Half-duplex: data is sent in both directions, but only one direction at a time.
- Full-duplex: data is sent in both directions at the same time.
- Serial.
- Because 80 m is a long distance and parallel data would suffer from skew.
- Half-duplex.
- Because data must travel both ways, but not at the same time.
- The player's moves must be sent to the server at the same time as game updates are received.
- Full-duplex allows data in both directions simultaneously, so there is no waiting / less lag.
- It is faster only over short distances, such as inside a computer.
- Over long distances skew corrupts the data, so serial is better (and cheaper, with fewer wires).
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.
Which description matches parallel data transmission?
- ASeveral bits are sent at once on several wires
- BOne bit is sent at a time down a single wire
- CData is sent in both directions at the same time
- DData is sent in one direction only
Two security guards use walkie-talkies. Only one guard can speak at a time; the other must wait until they have finished. Which method of transmission is this?
- AHalf-duplex
- BFull-duplex
- CSimplex
- DSerial only
What is meant by skew in data transmission?
- ABits sent at the same time arrive at slightly different times
- BBits are sent in the opposite direction to the one intended
- CBits are lost because the cable is too short
- DBits are sent one after another on a single wire
A computer sends data to a monitor. The monitor never sends data back. Which method of transmission is most suitable?
- ASimplex
- BHalf-duplex
- CFull-duplex
- DParallel half-duplex
A factory wants to send sensor data along a 300 m cable to a control room, and the control room must be able to send instructions back to the sensor unit at the same time. Which combination is most suitable?
- ASerial, full-duplex
- BParallel, full-duplex
- CSerial, simplex
- DParallel, half-duplex
Why is parallel transmission still used inside a computer, for example between the processor and memory, even though serial is used for long-distance links?
- AOver very short distances skew is negligible, so sending many bits at once is faster
- BParallel transmission can never suffer from skew inside a computer case
- CSerial transmission cannot carry data over distances shorter than one metre
- DParallel transmission needs fewer wires than serial transmission
Quiz key
Parallel transmission sends several bits simultaneously, each on its own wire. Sending one bit at a time on a single wire is serial. Both directions at once is full-duplex and one direction only is simplex: these describe direction, not how many bits are sent together.
Data travels in both directions but only one direction at a time, which is half-duplex. Full-duplex would let both guards talk at the same time, like a phone call. Simplex would allow only one guard ever to speak. Serial describes how many bits are sent at once, not the direction of the data.
Skew happens in parallel transmission: bits that left together on separate wires drift out of step and arrive at different times, corrupting the data. It has nothing to do with direction. Short cables reduce skew rather than cause loss. Sending bits one after another on one wire is serial transmission, which avoids skew.
Data only needs to go one way, from computer to monitor, so simplex is enough and is the simplest choice. Half-duplex and full-duplex both allow data to travel back, which the monitor never needs. 'Parallel half-duplex' still allows two-way traffic that is not needed.
Over 300 m, parallel transmission would suffer from skew, so serial is the reliable choice. Data must flow both ways at the same time, which needs full-duplex. Parallel, full-duplex has the right direction but the wrong method for long distances. Serial, simplex would stop the control room replying. Parallel, half-duplex has the skew problem and cannot send both ways at once.
Parallel sends several bits at the same time, so it is faster, and over a few centimetres the bits stay in step, so skew is not a problem. Skew can still occur in principle; it is just tiny over short distances. Serial works perfectly well over short distances (USB is an example). Parallel needs more wires than serial, not fewer: one per bit.
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.