Data loss

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Quick Questions

Shade in the A or B circle for each question.

1. A device sends 8 bytes of data but the receiver only gets 7 bytes. Which type of error is this?

A Data loss

B Data gain

2. Which statement describes data loss?

A Some bits or bytes that were sent never arrive

B Extra bits or bytes arrive that were never sent

3. The message HELLO is sent. The receiver gets HELO. What has happened?

A A byte was gained, so the message is longer

B A byte was lost, so the message is shorter

4. After a message is received, how can you spot data loss by comparing it with the message that was sent?

A The received message is longer

B The received message is shorter

5. A packet is sent as 10 bytes. Which received size would show data loss?

A 9 bytes

B 11 bytes

Match the Pairs

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

Left column		Right column
1Sent: 01001000 01101001 \| Received: 01001000		AData loss: one character (byte) went missing in transmission
2Sent: CAT \| Received: CT		BData loss: the second byte never arrived, so the message is shorter than the one sent
3Data loss means the received message is shorter than the sent message		CThe received message is longer, not shorter. An extra character means data gain, not data loss.
4Data loss happens when a byte that was sent never arrives		DSent: 11110000 10101010 00001111 \| Received: 11110000 00001111
5Sent: HELLO \| Received: HELLOO (data loss)		EIf all 8 bytes arrived, nothing is missing. Data loss needs the received message to be shorter than the sent one.
6Sent: 8 bytes \| Received: 8 bytes, but two bytes arrived missing, so data loss		Fsent = 5 bytes, received = 3 bytes

Definitions

data loss

Fill in the Blanks

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

sent ← "HELLO" received ← "HELO" OUTPUT ______(sent) - LENGTH(received)

sentCount ← 5 receivedCount ← 4 lostBytes ← sentCount _ receivedCount

IF LENGTH(received) _ LENGTH(sent) THEN OUTPUT "Data loss" ENDIF

IF lostBytes > 0 ____ OUTPUT "Byte missing" ENDIF

sent ← "A1B2C3" received ← "A1B2C" lostBytes ← LENGTH(sent) - LENGTH(________)

Spot the Error

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

Question 1

A sent <- "HELLO"

B got <- "HELO"

C IF LEN(got) > LEN(sent) THEN

D OUTPUT "Data loss"

E ENDIF

Question 2

A bytesSent <- 5

B bytesGot <- 4

C lost <- bytesGot - bytesSent

D OUTPUT lost

Question 3

A sent <- "DOG"

B got <- "DOGS"

C OUTPUT LEN(sent) - LEN(got)

Question 4

A sent <- MESSAGE

B got <- "MESAGE"

C shortBy <- LEN(sent) - LEN(got)

D OUTPUT shortBy

Question 5

A sent <- "HELLO"

B got <- "HLLO"

C lost <- LEN(sent) - LEN(got)

D IF lost < 0 THEN

E OUTPUT "Data loss"

F ENDIF

Answer Key

Data loss

Section A: Quick Questions

A — Data loss

A — Some bits or bytes that were sent never arrive

B — A byte was lost, so the message is shorter

B — The received message is shorter

A — 9 bytes

Section B: Match the Pairs

Sent: 01001000 01101001 | Received: 01001000 → Data loss: the second byte never arrived, so the message is shorter than the one sent

Sent: CAT | Received: CT → Data loss: one character (byte) went missing in transmission

Data loss means the received message is shorter than the sent message → sent = 5 bytes, received = 3 bytes

Data loss happens when a byte that was sent never arrives → Sent: 11110000 10101010 00001111 | Received: 11110000 00001111

Sent: HELLO | Received: HELLOO (data loss) → The received message is longer, not shorter. An extra character means data gain, not data loss.

Sent: 8 bytes | Received: 8 bytes, but two bytes arrived missing, so data loss → If all 8 bytes arrived, nothing is missing. Data loss needs the received message to be shorter than the sent one.

Section C: Definitions

data loss — When some bits or bytes that were sent never arrive, so the message that is received is shorter than the one that was sent.

Section D: Fill in the Blanks

sent ← "HELLO"
received ← "HELO"
OUTPUT LENGTH(sent) - LENGTH(received)

sentCount ← 5
receivedCount ← 4
lostBytes ← sentCount - receivedCount

IF LENGTH(received) < LENGTH(sent) THEN
  OUTPUT "Data loss"
ENDIF

IF lostBytes > 0 THEN
  OUTPUT "Byte missing"
ENDIF

sent ← "A1B2C3"
received ← "A1B2C"
lostBytes ← LENGTH(sent) - LENGTH(received)

Section E: Spot the Error

C — Data loss means the received message is shorter than the one sent. The test should be LEN(got) < LEN(sent), not >.

C — The number of bytes lost is the bytes sent minus the bytes received. The subtraction is the wrong way round and gives -1 instead of 1.

B — In data loss the received message is shorter than the sent one, so got should be "DO" (the G never arrived). "DOGS" is longer, which would be data gain.

A — The text that was sent is a string, so it must be written in quotes: sent <- "MESSAGE". Without quotes MESSAGE looks like a variable.

D — A positive value in lost means bytes went missing, so data loss is detected when lost > 0. Checking for < 0 would only be true if the message grew.