← IGCSE Computer Science Paper 1

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

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.

Part of: IGCSE Computer Science 0478 — 2.1 Data Transmission Types and Methods — Module 31

Understanding Advantages and disadvantages of simplex, half-duplex and full-duplex in IGCSE Computer Science Paper 1

What it does: Sending both ways at once is the advantage of full-duplex. The extra capacity needed is its disadvantage. Simplex is one-way only, so two devices never send at once and cannot collide. The trade-off is that the receiver cannot reply. Half-duplex is two-way, but not at the same time. Waiting for the other device's turn slows the exchange.

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

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Learning
Duo
Which is an advantage of simplex transmission?
No collisions, because data only travels one wayThe receiver can reply at the same time
Matches
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.
Applying
Meanings
Term
direction trade-off
Meaning
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.
Practice
SIMPLEX: one-way only, no collisions, no reply
Testing
Gaps
method ← ""
Check Answer
Spots
1Simplex: two-way at once
2Pro: no collisions

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Quick Questions

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 ✓
Simplex is one-way only, so two devices never send at once and cannot collide. The trade-off is that the receiver cannot reply.
2. Which is a disadvantage of simplex transmission?
A. The receiver cannot send anything back ✓
B. Both devices must take turns to send
Turn-taking belongs to half-duplex. The weakness of simplex is that there is no reply path at all.
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
Half-duplex is two-way, but not at the same time. Waiting for the other device's turn slows the exchange.
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
Half-duplex allows two-way transmission, but only by turns. Sending both ways at once is full-duplex.
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 ✓
Full-duplex gives the fastest two-way communication. It is not the cheapest, because it needs more capacity.

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.

Key Term

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.

Fill in the Blanks

1. IF direction = "one-way only" THEN method ← "simplex" ENDIF
Hint: Type the direction method that is simple and has no collisions but allows no reply.
2. IF devicesTakeTurns = TRUE THEN method ← "half-duplex" ENDIF
Hint: Type the two-way method that is slower because devices must wait for their turn.
3. IF bothWaysAtOnce = TRUE THEN method ← "full-duplex" ENDIF
Hint: Type the fastest two-way method, which sends and receives at the same time.
4. IF method = "simplex" THEN collisions ← FALSE ENDIF
Hint: Type the Boolean value that shows whether data collisions can happen when only one side sends.
5. IF method = "full-duplex" THEN channels ← 2 ENDIF
Hint: Type the number of channels needed so data can travel both ways at once, which is why it costs more.

Spot the Error

Question 1
A Simplex: two-way at once
B Pro: no collisions
C Con: receiver cannot reply
Line A — Simplex sends data in one direction only. The first line should be 'Simplex: one-way only', which is why the receiver cannot reply.
Question 2
A Half-duplex: two-way
B Devices take turns to send
C Pro: no waiting for a turn
Line 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'.
Question 3
A Full-duplex: two-way at once
B Pro: fastest for two-way use
C Con: needs less capacity
Line C — Sending both ways at the same time needs more capacity (bandwidth or channels), so the drawback is 'needs more capacity', not less.
Question 4
A Simplex: TV broadcast
B Half-duplex: walkie-talkie
C Full-duplex: phone call
D Phone call: take turns
Line D — A phone call is full-duplex, so both people can talk and hear at the same time. Taking turns describes half-duplex.
Question 5
A Half-duplex: walkie-talkie
B Pro: one-way on one channel
C Con: only one talks at a time
Line B — Half-duplex is two-way, with devices taking turns on one channel. Saying it is one-way describes simplex.

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