Why data is broken down into packets

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Quick Questions

Shade in the A or B circle for each question.

1. Why is a large file split into packets before it is sent across a network?

A So it can be sent in small, manageable pieces

B So it can be sent as one single block

2. A 20 MB video is sent over a network. What happens to the video?

A It is sent whole as a single packet

B It is split into many numbered packets

3. Which statement about packets and the network is correct?

A Small packets from many users can share the network at the same time

B One large file must use the whole network until it has finished

4. One packet of a file is lost on the way. What needs to be resent?

A Only the lost packet

B The whole file from the start

5. Why is each packet given a number?

A So the packet travels faster than the others

B So the pieces can be put back in order and a missing one can be spotted

Match the Pairs

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

Left column		Right column
1packet		ANumbers a piece of the file so the pieces can be put back in order at the destination
2packet_number = 3		Bpacket 7 lost -> resend packet 7
3A large file is split into numbered pieces before it is sent		CA small piece of a larger file, sent across the network on its own
4If one packet is lost, only that packet is resent, not the whole file		Dfile (12 MB) -> packet 1, packet 2, packet 3 ... packet 12
5packet 5 lost -> resend whole file		EOnly the lost packet needs to be resent. Resending the whole file wastes time and network capacity.
6One 500 MB file sent as one piece, so it takes over the network until it is done		FA large file sent as a single piece blocks other users. Packets let many users share the network.

Definitions

packet

Fill in the Blanks

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

packets ← _____(file, 100)

FOR number ← 1 TO 5 SEND(packets[______]) NEXT number

IF packetLost = TRUE THEN ______(packetNumber) ENDIF

totalPackets ← fileSize ___ packetSize

WHILE packetNumber <= totalPackets SEND(packets[packetNumber]) packetNumber ← packetNumber _ 1

Spot the Error

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

Question 1

A total ← 1200

B size ← 100

C packets ← total * size

D OUTPUT packets

Question 2

A FOR n ← 1 TO 5

B packet.number ← n

C packet.data ← piece[n]

D SEND file

E NEXT n

Question 3

A FOR n ← 1 TO 10

B IF ack[n] = FALSE THEN

C lostCount ← lostCount + 1

D RESEND file

E ENDIF

F NEXT n

Question 4

A IF fileSize < packetSize THEN

B SPLIT file INTO packets

C SEND each packet

D ENDIF

Question 5

A FOR n ← 1 TO count

B packet[n].number ← 1

C SEND packet[n]

D NEXT n

Answer Key

Why data is broken down into packets

Section A: Quick Questions

A — So it can be sent in small, manageable pieces

B — It is split into many numbered packets

A — Small packets from many users can share the network at the same time

A — Only the lost packet

B — So the pieces can be put back in order and a missing one can be spotted

Section B: Match the Pairs

packet → A small piece of a larger file, sent across the network on its own

packet_number = 3 → Numbers a piece of the file so the pieces can be put back in order at the destination

A large file is split into numbered pieces before it is sent → file (12 MB) -> packet 1, packet 2, packet 3 ... packet 12

If one packet is lost, only that packet is resent, not the whole file → packet 7 lost -> resend packet 7

packet 5 lost -> resend whole file → Only the lost packet needs to be resent. Resending the whole file wastes time and network capacity.

One 500 MB file sent as one piece, so it takes over the network until it is done → A large file sent as a single piece blocks other users. Packets let many users share the network.

Section C: Definitions

packet — A small piece of a larger file. Data is split into numbered packets so they share the network and a lost packet can be resent instead of the whole file.

Section D: Fill in the Blanks

packets ← SPLIT(file, 100)

FOR number ← 1 TO 5
   SEND(packets[number])
NEXT number

IF packetLost = TRUE THEN
   RESEND(packetNumber)
ENDIF

totalPackets ← fileSize DIV packetSize

WHILE packetNumber <= totalPackets
   SEND(packets[packetNumber])
   packetNumber ← packetNumber + 1

Section E: Spot the Error

C — The number of packets is the file size divided by the packet size, so it needs DIV (1200 DIV 100 = 12). Multiplying gives a meaningless number.

D — Each loop should send one small numbered packet, not the whole file. The line should be SEND packet.

D — Only the lost packet needs to be sent again, which is the benefit of using packets. It should be RESEND packet[n], not the whole file.

A — A file only needs splitting when it is larger than the packet size, so the comparison should be >, not <.

B — Each packet needs its own number so the pieces can be put back in order. The number should be n, not 1 for every packet.