← IGCSE Computer Science Paper 1

Simplex data transmission

Data transmission in one direction only, from sender to receiver, with no reply possible. Example: a keyboard sending key presses to a computer.

Part of: IGCSE Computer Science 0478 — 2.1 Data Transmission Types and Methods — Module 28, WA Computer Science ATAR Year 11 — Network Communications — Module 20

Understanding Simplex data transmission in IGCSE Computer Science Paper 1

What it does: The single arrow shows data moving one way only, so no reply is possible. Data flows from the computer to the printer and the printer does not send data back, which makes it simplex. Simplex means one direction only. Sending in both directions, one way at a time, is half-duplex. Simplex has no reply route, so the receiver cannot confirm receipt or ask for data to be resent. Simplex never allows data to flow both ways, so a double arrow is a mistake.

Common mistakes: Simplex sends data in one direction only. The direction should be 'one way', not 'two way'. In simplex transmission no reply is possible, so reply_possible must be FALSE.

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This module's key terms are also in a printable crossword (Modules 131–141) and word search (Modules 121–141).

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Learning

Duo

Which statement describes simplex transmission?

Data travels in one direction only, from sender to receiverData travels in both directions, but only one way at a time

Matches

simplex: sender <-> receiver

↓

The two-way arrow is wrong. Simplex is one direction only, so it should be sender -> receiver. Two-way arrows show duplex.

Applying

Meanings

Term

simplex

Meaning

Data transmission in one direction only, from sender to receiver, with no reply possible. Example: a keyboard sending key presses to a computer.

Practice

sender ← "keyboard"

Testing

Gaps

mode =

Check Answer

Spots

1mode ← 'simplex'

2direction ← 'two way'

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Quick Questions

1. Which statement describes simplex transmission?

A. Data travels in both directions, but only one way at a time

B. Data travels in one direction only, from sender to receiver ✓

Simplex means one direction only. Sending in both directions, one way at a time, is half-duplex.

2. A keyboard sends key presses to a computer. Which type of transmission is this?

A. Simplex ✓

B. Full-duplex

The keyboard only sends data to the computer and never receives data back through that link, so it is simplex.

3. In simplex transmission, can the receiver send a reply back to the sender along the same link?

A. Yes, it can reply at any time

B. No, no reply is possible ✓

Simplex is one-way only, so the receiver cannot send data back along the same link.

4. A computer sends a document to a printer. Which description fits the data flow if only the computer sends data?

A. Simplex: data goes from computer to printer only ✓

B. Full-duplex: both devices send at the same time

If data only flows from the computer to the printer, it is simplex. Full-duplex needs both devices to send at the same time.

5. Which direction does data travel in simplex transmission?

A. Sender to receiver only ✓

B. Sender to receiver and receiver to sender

Simplex is a single direction. Two directions would be half-duplex or full-duplex.

Match the Pairs

simplex → Data travels in one direction only, from sender to receiver

keyboard -> computer → Simplex example: key presses go to the computer and nothing comes back

In simplex transmission, the receiver cannot send a reply to the sender → sender -> receiver

Sending a document to a printer in one direction only is an example of simplex → computer -> printer

simplex: sender <-> receiver → The two-way arrow is wrong. Simplex is one direction only, so it should be sender -> receiver. Two-way arrows show duplex.

simplex: keyboard <- computer → The arrow points the wrong way. Key presses go from the keyboard to the computer, so it should be keyboard -> computer.

Key Term

simplex

Data transmission in one direction only, from sender to receiver, with no reply possible. Example: a keyboard sending key presses to a computer.

Fill in the Blanks

1. mode = SIMPLEX

Hint: Type the constant naming the transmission mode where data travels in one direction only.

2. SEND keypress FROM keyboard TO computer

Hint: Type the device that receives the data from the keyboard.

3. SEND document FROM computer TO printer

Hint: Type the device that receives the data and cannot reply.

4. IF mode = SIMPLEX THEN reply = FALSE

Hint: Type the Boolean value showing that the receiver cannot send a reply.

5. mode = SIMPLEX directions = 1

Hint: Type the number of directions data can travel in this mode.

Spot the Error

Question 1

A mode ← 'simplex'

B direction ← 'two way'

C sender ← 'keyboard'

D receiver ← 'computer'

Line B — Simplex sends data in one direction only. The direction should be 'one way', not 'two way'.

Question 2

A IF mode = 'simplex' THEN

B sender ← 'keyboard'

C receiver ← 'computer'

D reply_possible ← TRUE

E ENDIF

Line D — In simplex transmission no reply is possible, so reply_possible must be FALSE.

Question 3

A sender ← 'computer'

B receiver ← 'printer'

C SEND document TO sender

Line C — Data travels from the sender to the receiver. The document must be sent TO the receiver (the printer), not back to the sender.

Question 4

A sender ← 'keyboard'

B receiver ← 'computer'

C SEND key TO receiver

D mode ← 'half-duplex'

Line D — A keyboard only sends key presses one way to the computer. That is simplex, not half-duplex, which allows both directions at different times.

Question 5

A IF direction = 'both ways' THEN

B OUTPUT 'simplex'

C ELSE

D OUTPUT 'not simplex'

E ENDIF

Line A — Simplex means data goes one way only. The test should check for 'one way', otherwise the program labels two-way transmission as simplex.

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