Half-duplex data transmission

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Quick Questions

Shade in the A or B circle for each question.

1. Which statement describes half-duplex transmission?

A Data travels in both directions at the same time

B Data travels in both directions, but only one direction at a time

2. Which device is an example of half-duplex transmission?

A A telephone call

B A walkie-talkie

3. Two devices use half-duplex. Device A is sending data. What must Device B do?

A Wait until Device A has finished sending

B Send its own data at the same time

4. True or false: half-duplex data can travel in only ONE direction ever.

A False: it can travel both ways, but not at the same time

B True: it only ever travels one way

5. What is the key idea behind half-duplex transmission?

A Devices take turns to send and receive

B Devices send and receive at the same moment

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1half-duplex		AData can travel in both directions, but only one direction at a time, so devices take turns
2walkie-talkie		BA half-duplex example: one person speaks while the other listens, then they swap
3Half-duplex lets two devices send data both ways, but never at the same moment		Cif channel_busy: wait()
4In half-duplex, a device must wait for its turn before it can send		DThis describes full-duplex, not half-duplex. In half-duplex, data goes both ways but only one direction at a time.
5Half-duplex: A <-> B at the same time		EThis describes simplex, not half-duplex. Half-duplex can send in both directions, just not at once.
6Half-duplex: A -> B only, never B -> A		FA -> B, then B -> A (one at a time)

Definitions

half-duplex

Fill in the Blanks

Complete each line of code by filling in the missing parts.

mode ← "___________"

maxSenders ← _

IF channelBusy THEN ____ ENDIF

IF mode _ "half-duplex" THEN takeTurns() ENDIF

IF channelFree THEN SEND(data) ____ WAIT ENDIF

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A mode ← "half-duplex"

B directions ← 1

C sendAtOnce ← FALSE

Question 2

A type ← "half-duplex"

B bothDirections ← TRUE

C simultaneous ← TRUE

Question 3

A IF talking = "A" THEN

B A sends data to B

C ELSE

D A sends data to B

E ENDIF

Question 4

A direction1 ← "A to B"

B direction2 ← "B to A"

C usedAtOnce ← 2

D // one direction at a time

Question 5

A transmission ← "full-duplex"

B devices take turns to send

C walkie-talkie is an example

Answer Key

Half-duplex data transmission

Section A: Quick Questions

B — Data travels in both directions, but only one direction at a time

B — A walkie-talkie

A — Wait until Device A has finished sending

A — False: it can travel both ways, but not at the same time

A — Devices take turns to send and receive

Section B: Match the Pairs

half-duplex → Data can travel in both directions, but only one direction at a time, so devices take turns

walkie-talkie → A half-duplex example: one person speaks while the other listens, then they swap

Half-duplex lets two devices send data both ways, but never at the same moment → A -> B, then B -> A (one at a time)

In half-duplex, a device must wait for its turn before it can send → if channel_busy: wait()

Half-duplex: A <-> B at the same time → This describes full-duplex, not half-duplex. In half-duplex, data goes both ways but only one direction at a time.

Half-duplex: A -> B only, never B -> A → This describes simplex, not half-duplex. Half-duplex can send in both directions, just not at once.

Section C: Definitions

half-duplex — Data can travel in both directions, but only one direction at a time, so devices take turns, like a walkie-talkie.

Section D: Fill in the Blanks

mode ← "half-duplex"

maxSenders ← 1

IF channelBusy THEN
  WAIT
ENDIF

IF mode = "half-duplex" THEN
  takeTurns()
ENDIF

IF channelFree THEN SEND(data)
ELSE WAIT
ENDIF

Section E: Spot the Error

B — Half-duplex data can travel in both directions, so directions should be 2. A value of 1 describes simplex.

C — In half-duplex the two directions are never used at the same time. Devices take turns, so simultaneous should be FALSE.

D — When it is not A's turn (the ELSE branch), B should send data to A. Having A send in both branches means the devices never swap turns.

C — Half-duplex has two directions available, but only one can be used at any moment. usedAtOnce should be 1, not 2.

A — The program describes devices taking turns, which is half-duplex. Full-duplex lets both devices send at the same time.