Packets arriving out of order

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Packets 1 to 6 are sent in order. Which statement is true about how they arrive?

A They always arrive in the order 1 to 6

B They may arrive in a different order

2. Why can packet 5 arrive before packet 4?

A Packet 5 took a faster route

B Packet 5 was sent before packet 4

3. Is the order of arrival of packets guaranteed?

A No, order is not guaranteed

B Yes, order is always guaranteed

4. What is the main reason packets arrive out of order?

A They take different routes to the destination

B They are all sent at the same time on one wire

5. Packets arrive in the order 1, 2, 3, 5, 4. What has happened?

A Packet 4 was lost and never sent

B Packet 5 arrived before packet 4

Match the Pairs

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

Left column		Right column
1Sent: 1, 2, 3, 4, 5 \| Arrived: 1, 2, 3, 5, 4		AThe packets arrived out of order because packet 5 reached the destination before packet 4
2Packet 4: Route A (busy) \| Packet 5: Route B (quiet)		BWrong: packet 4 has not necessarily been lost. It may have taken a slower route and still be on its way.
3The order in which packets arrive is not guaranteed, because each packet may take a different route		CPacket 5 can overtake packet 4 because it took a faster route
4The destination uses the packet number in each header to put out-of-order packets back into the correct order		Dsort(packets, by packet_number)
5Packets always arrive in the order they were sent		Earrival_order != sending_order
6Packet 5 arrived before packet 4, so packet 4 must be lost		FWrong: packets take different routes, so they may arrive in a different order. The order is not guaranteed.

Definitions

packets arrive out of order

Fill in the Blanks

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

Sent 1 2 3 4 5, arrived 1 2 3 _ 4

__ arrivalOrder != sentOrder THEN

SORT packets BY ____________

orderGuaranteed = _____

IF packet5Arrived AND ___ packet4Arrived

Spot the Error

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

Question 1

A # Packet 5 arrives before 4

B arrived = [1, 2, 3, 4, 5]

C print(arrived)

Question 2

A packets_sent = [1, 2, 3, 4]

B order_guaranteed = True

C if not order_guaranteed:

D print('Reorder needed')

Question 3

A route_4 = 'short'

B route_5 = 'short'

C # So packet 5 arrives first

Question 4

A arrived = [5, 4, 6]

B sent = [4, 5, 6]

C if arrived == sent:

D print('Out of order')

Question 5

A arrived = [3, 1, 2

B arrived.sort()

C print(arrived)

Answer Key

Packets arriving out of order

Section A: Quick Questions

B — They may arrive in a different order

A — Packet 5 took a faster route

A — No, order is not guaranteed

A — They take different routes to the destination

B — Packet 5 arrived before packet 4

Section B: Match the Pairs

Sent: 1, 2, 3, 4, 5 | Arrived: 1, 2, 3, 5, 4 → The packets arrived out of order because packet 5 reached the destination before packet 4

Packet 4: Route A (busy) | Packet 5: Route B (quiet) → Packet 5 can overtake packet 4 because it took a faster route

The order in which packets arrive is not guaranteed, because each packet may take a different route → arrival_order != sending_order

The destination uses the packet number in each header to put out-of-order packets back into the correct order → sort(packets, by packet_number)

Packets always arrive in the order they were sent → Wrong: packets take different routes, so they may arrive in a different order. The order is not guaranteed.

Packet 5 arrived before packet 4, so packet 4 must be lost → Wrong: packet 4 has not necessarily been lost. It may have taken a slower route and still be on its way.

Section C: Definitions

packets arrive out of order — Packets take different routes, so they may reach the destination in a different order from the one sent, e.g. packet 5 before packet 4. Order is not guaranteed.

Section D: Fill in the Blanks

Sent 1 2 3 4 5, arrived 1 2 3 5 4

IF arrivalOrder != sentOrder THEN

SORT packets BY packetNumber

orderGuaranteed = FALSE

IF packet5Arrived AND NOT packet4Arrived

Section E: Spot the Error

B — The comment says packet 5 arrives before packet 4, but this list has them in order. It should be [1, 2, 3, 5, 4].

B — Packets take different routes, so the order of arrival is not guaranteed. The variable should be False, which means the reorder step runs.

A — For packet 5 to arrive before packet 4, packet 4 must take the longer route. Packet 4's route should be 'long', not 'short'.

C — The packets are out of order when the arrival order is different from the sent order. The test should use != not ==.

A — The list is missing its closing square bracket. It should be arrived = [3, 1, 2], showing packets that arrived out of order.