Data change

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Sent: 01000001. Received: 01000011. What type of error is this?

A Data change

B Data loss

2. Which statement describes data change?

A The same amount of data arrives, but some bits have wrong values

B Fewer bits arrive than were sent

3. A 0 flips to a 1 during transmission. This is an example of:

A Data change

B Data gain

4. Sent: 1100 0011. Received: 1100 0111. How many bits have changed?

A 2

B 1

5. Sent character: A. Received character: C. What has most likely happened?

A The character was lost on the way

B Some bits changed, so a different character arrived

Match the Pairs

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

Left column		Right column
1Sent: 01000001 Received: 01000011		ASent: 11001100 (8 bits) Received: 11001000 (8 bits)
2Sent: 'A' Received: 'C'		BSent: 1 0 1 1 0 0 1 0 Received: 1 0 1 0 0 0 1 0
3Comparing the sent and received bits position by position shows which bit was altered		CThe sent and received bits are identical, so nothing has changed and the data arrived correctly.
4In data change the length stays the same: 8 bits are sent and 8 bits arrive, but one value is wrong		DOnly 3 bits arrived instead of 4, so a bit was lost. That is data loss, not data change.
5Sent: 1010 Received: 101 -> data change		EData change: one bit has flipped from 0 to 1, so the same number of bits arrived but one value is wrong
6Sent: 0110 Received: 0110 -> data change		FA changed character: the letter that arrived is different from the letter that was sent

Definitions

data change

Fill in the Blanks

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

Sent: 01000001 Received: 01000011 Error type: ___________

IF sent __ received THEN OUTPUT "Data change" ENDIF

IF LENGTH(sent) _ LENGTH(received) THEN OUTPUT "Same amount of data" ENDIF

Sent bit: 0 Received bit: _ Bit flipped from 0 to 1

FOR i ← 1 TO 8 IF sent[i] <> received[_] THEN OUTPUT "Bit changed"

Spot the Error

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

Question 1

A sent ← 01000001

B received ← 010000011

C IF sent ≠ received THEN

D OUTPUT "Data change"

E ENDIF

Question 2

A sent ← 10110010

B received ← 10100010

C IF sent = received THEN

D OUTPUT "Data change"

E ENDIF

Question 3

A count ← 0

B FOR i ← 1 TO 8

C IF S[i] = R[i] THEN

D count ← count + 1

E ENDIF

F NEXT i

Question 4

A sent ← A

B received ← "B"

C IF sent ≠ received THEN

D OUTPUT "Character changed"

Question 5

A sent ← "11011100"

B received ← "11011100"

C IF sent[4] ≠ received[4] THEN

D OUTPUT "Bit 4 flipped"

Answer Key

Data change

Section A: Quick Questions

A — Data change

A — The same amount of data arrives, but some bits have wrong values

A — Data change

B — 1

B — Some bits changed, so a different character arrived

Section B: Match the Pairs

Sent: 01000001 Received: 01000011 → Data change: one bit has flipped from 0 to 1, so the same number of bits arrived but one value is wrong

Sent: 'A' Received: 'C' → A changed character: the letter that arrived is different from the letter that was sent

Comparing the sent and received bits position by position shows which bit was altered → Sent: 1 0 1 1 0 0 1 0 Received: 1 0 1 0 0 0 1 0

In data change the length stays the same: 8 bits are sent and 8 bits arrive, but one value is wrong → Sent: 11001100 (8 bits) Received: 11001000 (8 bits)

Sent: 1010 Received: 101 -> data change → Only 3 bits arrived instead of 4, so a bit was lost. That is data loss, not data change.

Sent: 0110 Received: 0110 -> data change → The sent and received bits are identical, so nothing has changed and the data arrived correctly.

Section C: Definitions

data change — Bits arrive altered, such as a 0 flipping to a 1, so the same amount of data arrives but with wrong values. Comparing sent and received bits shows it.

Section D: Fill in the Blanks

Sent:     01000001
Received: 01000011
Error type: data change

IF sent <> received THEN
  OUTPUT "Data change"
ENDIF

IF LENGTH(sent) = LENGTH(received) THEN
  OUTPUT "Same amount of data"
ENDIF

Sent bit: 0
Received bit: 1
Bit flipped from 0 to 1

FOR i ← 1 TO 8
  IF sent[i] <> received[i] THEN
    OUTPUT "Bit changed"

Section E: Spot the Error

B — The received value has 9 bits, so an extra bit has arrived. That is data gain, not data change. Data change keeps the same number of bits, so it should be 01000011 (8 bits) with one bit flipped.

C — The test is the wrong way round. Data change is detected when the sent and received bits are NOT equal, so it should be IF sent ≠ received THEN.

C — This counts the bits that match, not the bits that changed. To count flipped bits, it should test IF S[i] ≠ R[i] THEN.

A — The character A must be written in quotes as a string. Without quotes, A is treated as a variable name. It should be sent ← "A".

A — The sent data must be 11001100 so that bit 4 is 0 when sent and 1 when received, which shows a flipped bit. With 11011100, nothing changed.