Advantages and disadvantages of simplex, half-duplex and full-duplex

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Quick Questions

Shade in the A or B circle for each question.

1. Which is an advantage of simplex transmission?

A The receiver can reply at the same time

B No collisions, because data only travels one way

2. Which is a disadvantage of simplex transmission?

A The receiver cannot send anything back

B Both devices must take turns to send

3. Why is half-duplex slower than full-duplex for a two-way conversation?

A Devices must take turns, so only one can send at a time

B Data can only ever travel in one direction

4. Which is an advantage of half-duplex over simplex?

A Data can travel in both directions

B Data travels in both directions at the same time

5. Which is an advantage of full-duplex transmission?

A It is the cheapest and simplest method to set up

B Both devices can send and receive at the same time, so it is fastest for two-way

Match the Pairs

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

Left column		Right column
1simplex		AData travels both ways but only one direction at a time, so devices must take turns and it is slower
2half-duplex		BData travels one way only, so there are no collisions but the receiver cannot reply
3Full-duplex lets both devices send and receive at the same moment, which is fastest for two-way use but needs more capacity and costs more		CSimplex is one-way only, so the receiver cannot reply. Its advantages are that it is simple and has no collisions.
4A trade-off comparison: simplex = one-way only, half-duplex = two-way by turns, full-duplex = two-way at once		Dfull-duplex
5Simplex is best because the receiver can reply at any time		EIn half-duplex the devices cannot send together. They take turns, so it is slower than full-duplex.
6Half-duplex is as fast as full-duplex because both send together		Fsimplex < half-duplex < full-duplex

Definitions

direction trade-off

Fill in the Blanks

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

IF direction = "one-way only" THEN method ← "_______" ENDIF

IF devicesTakeTurns = TRUE THEN method ← "___________" ENDIF

IF bothWaysAtOnce = TRUE THEN method ← "___________" ENDIF

IF method = "simplex" THEN collisions ← _____ ENDIF

IF method = "full-duplex" THEN channels ← _ ENDIF

Spot the Error

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

Question 1

A Simplex: two-way at once

B Pro: no collisions

C Con: receiver cannot reply

Question 2

A Half-duplex: two-way

B Devices take turns to send

C Pro: no waiting for a turn

Question 3

A Full-duplex: two-way at once

B Pro: fastest for two-way use

C Con: needs less capacity

Question 4

A Simplex: TV broadcast

B Half-duplex: walkie-talkie

C Full-duplex: phone call

D Phone call: take turns

Question 5

A Half-duplex: walkie-talkie

B Pro: one-way on one channel

C Con: only one talks at a time

Answer Key

Advantages and disadvantages of simplex, half-duplex and full-duplex

Section A: Quick Questions

B — No collisions, because data only travels one way

A — The receiver cannot send anything back

A — Devices must take turns, so only one can send at a time

A — Data can travel in both directions

B — Both devices can send and receive at the same time, so it is fastest for two-way

Section B: Match the Pairs

simplex → Data travels one way only, so there are no collisions but the receiver cannot reply

half-duplex → Data travels both ways but only one direction at a time, so devices must take turns and it is slower

Full-duplex lets both devices send and receive at the same moment, which is fastest for two-way use but needs more capacity and costs more → full-duplex

A trade-off comparison: simplex = one-way only, half-duplex = two-way by turns, full-duplex = two-way at once → simplex < half-duplex < full-duplex

Simplex is best because the receiver can reply at any time → Simplex is one-way only, so the receiver cannot reply. Its advantages are that it is simple and has no collisions.

Half-duplex is as fast as full-duplex because both send together → In half-duplex the devices cannot send together. They take turns, so it is slower than full-duplex.

Section C: Definitions

direction trade-off — Simplex is one-way only but simple and has no collisions. Half-duplex is two-way by turns, so slower. Full-duplex is two-way at once and fastest, but needs more capacity and costs more.

Section D: Fill in the Blanks

IF direction = "one-way only" THEN
  method ← "simplex"
ENDIF

IF devicesTakeTurns = TRUE THEN
  method ← "half-duplex"
ENDIF

IF bothWaysAtOnce = TRUE THEN
  method ← "full-duplex"
ENDIF

IF method = "simplex" THEN
  collisions ← FALSE
ENDIF

IF method = "full-duplex" THEN
  channels ← 2
ENDIF

Section E: Spot the Error

A — Simplex sends data in one direction only. The first line should be 'Simplex: one-way only', which is why the receiver cannot reply.

C — Half-duplex devices must take turns, so there is waiting. Its drawback is that it is slower than full-duplex, so the line should be 'Con: slower than full-duplex'.

C — Sending both ways at the same time needs more capacity (bandwidth or channels), so the drawback is 'needs more capacity', not less.

D — A phone call is full-duplex, so both people can talk and hear at the same time. Taking turns describes half-duplex.

B — Half-duplex is two-way, with devices taking turns on one channel. Saying it is one-way describes simplex.