Packet switching

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Quick Questions

Shade in the A or B circle for each question.

1. Which statement about packet switching is correct?

A A message is always sent as one single block

B A message is split into packets that are sent separately

2. How is each packet routed in packet switching?

A All packets must follow the same fixed route

B Each packet is routed on its own

3. What passes packets across the network from one point to the next?

A Routers pass packets on from router to router

B The receiving computer picks every packet's route

4. What happens to the packets when they reach the destination?

A They are joined back together in the right order

B They are kept apart and read separately

5. Which is the correct order of the packet switching process?

A Split into packets, send separately, rejoin at destination

B Send as one block, split at destination, rejoin at router

Match the Pairs

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

Left column		Right column
1packet switching		APacket switching splits the message into separate packets. It does not send one block, and each packet is routed on its own.
2Packet 3 of 8 reaches the destination		BData is split into packets that are sent separately across a network, each routed on its own from router to router.
3In packet switching, a message is broken into packets before it is sent		Cmessage -> [packet 1][packet 2][packet 3]
4Each packet is passed from router to router and is routed on its own		DOne of the separate packets has arrived, and it will be joined back together with the others in the right order.
5Packet switching sends the whole message as one single block along one fixed route.		EPacket 2: Router A -> Router C -> Router D
6Packets arrive at the destination and stay in separate pieces, so the message is never rebuilt.		FThe packets are joined back together in the right order at the destination to rebuild the original message.

Definitions

packet switching

Fill in the Blanks

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

packets ← _____(message, 4)

FOR EACH p IN packets ____(p, router)

ordered ← ____(received, packetNumber)

message ← ____(ordered)

total ← LENGTH(packets) IF count = _____ THEN message ← JOIN(ordered)

Spot the Error

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

Question 1

A message ← "HELLO WORLD"

B packets ← SPLIT(message, 4)

C FOR EACH p IN message

D SEND(p)

Question 2

A p1 ← "HELL"

B p2 ← "O WO"

C SEND(p1 + p2, route1)

D SEND(p2, route2)

Question 3

A packet ← RECEIVE()

B next ← BEST_ROUTE(packet)

C FORWARD(message, next)

Question 4

A received ← FIRST_PACKET()

B SORT(received, BY number)

C message ← JOIN(received)

D OUTPUT message

Question 5

A message ← "GOOD MORNING"

B packets ← JOIN(message, 4)

C OUTPUT LENGTH(packets)

Answer Key

Packet switching

Section A: Quick Questions

B — A message is split into packets that are sent separately

B — Each packet is routed on its own

A — Routers pass packets on from router to router

A — They are joined back together in the right order

A — Split into packets, send separately, rejoin at destination

Section B: Match the Pairs

packet switching → Data is split into packets that are sent separately across a network, each routed on its own from router to router.

Packet 3 of 8 reaches the destination → One of the separate packets has arrived, and it will be joined back together with the others in the right order.

In packet switching, a message is broken into packets before it is sent → message -> [packet 1][packet 2][packet 3]

Each packet is passed from router to router and is routed on its own → Packet 2: Router A -> Router C -> Router D

Packet switching sends the whole message as one single block along one fixed route. → Packet switching splits the message into separate packets. It does not send one block, and each packet is routed on its own.

Packets arrive at the destination and stay in separate pieces, so the message is never rebuilt. → The packets are joined back together in the right order at the destination to rebuild the original message.

Section C: Definitions

packet switching — Data is split into packets that are sent separately, each routed on its own from router to router, then joined back together in the right order at the destination.

Section D: Fill in the Blanks

packets ← SPLIT(message, 4)

FOR EACH p IN packets
    SEND(p, router)

ordered ← SORT(received, packetNumber)

message ← JOIN(ordered)

total ← LENGTH(packets)
IF count = total THEN
    message ← JOIN(ordered)

Section E: Spot the Error

C — In packet switching the loop must go through the packets, not the whole message. It should be FOR EACH p IN packets, so each packet is sent separately.

C — Packets are sent separately, not stuck together. Line 3 should be SEND(p1, route1), and p2 is sent on its own in the next line.

C — A router passes on one packet at a time and never sees the whole message. It should forward the packet: FORWARD(packet, next).

A — The destination needs all the packets to join the message back together. It should collect them all with ALL_PACKETS(), not only the first packet.

B — At the sender the message is broken into packets, so it must use SPLIT, not JOIN. The correct line is packets ← SPLIT(message, 4).