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9618Paper 3 · Advanced Theory§14.1, §14.2

14. Communication and Internet Technologies

Protocols (TCP/IP stack, HTTP, FTP, SMTP, POP3, IMAP, BitTorrent), circuit and packet switching in depth.

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Statometer49RegularNext Paper 392%
Marks a paper7.6 · 10%Rank#6 of 8 · #4 on P3Trend · last 12→Oct/Nov 24 · 31: 9 marksOct/Nov 24 · 32: 14 marksOct/Nov 24 · 33: 9 marksMay/Jun 25 · 31: 9 marksMay/Jun 25 · 32: 13 marksMay/Jun 25 · 33: 9 marksOct/Nov 25 · 31: 10 marksOct/Nov 25 · 32: 10 marksOct/Nov 25 · 33: 10 marksMay/Jun 26 · 31: 4 marksMay/Jun 26 · 32: 4 marksMay/Jun 26 · 33: 4 marks9 in 10 chance in the next paper

Everything for this topic — study hub

A2 Level · 9618 · Paper 3

Statometer — what 32 real papers say about this topic and each of its 2 syllabus bullets

Regular · #6 of 8 in A2 Level · recomputed with every new session

49REGULAR
Regular#6 of 8 in A2 Level#4 on Paper 3→ Steady

Comes up most sessions for a few marks — know the definitions and one worked example.

Next Paper 3
92%
9 in 10 chance it is set
Marks a paper
7.6 / 75
10% of Paper 3 · fair share 17%
Appeared in
31 / 32
Paper 3 sittings 2021–2026
Last set
May/Jun 2026
9618/33 · Q2 · 4 marks · 11-series streak
Marks in each of the last 12 Paper 3 sittingsOct/Nov 24 → May/Jun 26
Oct/Nov 24 · 31: 9 marksOct/Nov 24 · 32: 14 marksOct/Nov 24 · 33: 9 marksMay/Jun 25 · 31: 9 marksMay/Jun 25 · 32: 13 marksMay/Jun 25 · 33: 9 marksOct/Nov 25 · 31: 10 marksOct/Nov 25 · 32: 10 marksOct/Nov 25 · 33: 10 marksMay/Jun 26 · 31: 4 marksMay/Jun 26 · 32: 4 marksMay/Jun 26 · 33: 4 marks

What the papers say

  • Set in 31 of 32 Paper 3 sittings on the current syllabus — treat it as certain.
  • Worth about 7.6 marks a paper (10% of Paper 3).
  • Last set May/Jun 2026 · 9618/33 · Q2 for 4 marks — in the most recent series.
  • Set in each of the last 11 series without a miss.
  • Steady at around 7.7 marks a paper year on year.
  • Lives on “Describe” and “State” — 57% of its questions: full sentences with a reason, not one-word answers.
  • Its biggest question so far: 10 marks (Oct/Nov 2025 · 9618/31 · Q3).
  • Inside the topic, §14.1 Protocols carries the most marks (55%) and §14.2 Circuit switching and packet switching the least (45%).
  • It is examined almost entirely as AO1 (Knowledge & understanding, 93%) — definitions and descriptions in syllabus words score.
  • The examiner has commented on 21 of its questions — read “What the examiner said” before you practise.

Command words

Share of questions using the word (a question can use several). What each wants →

Question shapes

  • ≤ 6 mk29
  • 7–9 mk10
  • 10–12 mk3
  • 13–15 mk0
  • 16+ mk0

Average 5.9 marks a question · 19% with a figure or table · 10% with code · biggest 10 marks

Assessment objectives — how it is examined

Every part of every current-syllabus question filed under Cambridge's AO1 / AO2 / AO3 (from its command word and what it asks you to do), so you know whether this topic pays for definitions, for applying, or for judging and building.

  • AO1 Knowledge & understanding
  • AO2 Apply & analyse
  • AO3 Design, program & evaluate

Paper 3 as a whole

Paper 3SyllabusMeasured
AO1 Knowledge & understanding60%54%
AO2 Apply & analyse40%46%
AO3 Design, program & evaluate0%0%

Syllabus = Cambridge's grid; measured = the bank's current-syllabus papers.

Inside the topic — every syllabus bullet, measured

Each part of each question is filed under the bullet it examines; the numbers are per Paper 3 sitting, exactly like the topic's. Open a bullet for its own Statometer.

  • 14.1Protocols#5 of 14 on Paper 3Core · 6882% next paper4.7 marks24/32 sittings↗ May/Jun 2026

    A regular earner inside the topic — most papers touch it.Syllabus: why protocols are essential; protocol stacks; the four-layer TCP/IP suite and what happens when a message crosses the internet; HTTP, FTP, POP3, IMAP, SMTP and BitTorrent

    Next Paper 3
    82%
    8 in 10
    Marks a paper
    4.7
    6% of the paper · 55% of the topic
    Asked in
    24 / 32
    Paper 3 sittings · 27 questions
    Last asked
    May/Jun 2026
    9618/33 · Q2 · 4 marks · 6-series streak
    • Asked in 24 of 32 Paper 3 sittings — about 8 papers in 10.
    • About 4.7 marks a paper (6% of Paper 3; 55% of the topic's marks across its 2 bullets).
    • Last asked May/Jun 2026 · 9618/33 · Q2 (4 marks) — in the most recent series.
    • Asked in each of the last 6 series.
    • Rising: 2.5 → 5.5 marks a paper.
    • Usually “Describe”: full sentences with a reason, not one-word answers.
    • Biggest chunk of marks so far: 8 in May/Jun 2022 · 9618/32 · Q3.
    • It is examined almost entirely as AO1 (Knowledge & understanding, 94%) — definitions and descriptions in syllabus words score.
    Last 12 sittings↗ Rising
    Oct/Nov 24 · 31: 4 marksOct/Nov 24 · 32: 7 marksOct/Nov 24 · 33: 4 marksMay/Jun 25 · 31: 5 marksMay/Jun 25 · 32: 9 marksMay/Jun 25 · 33: 5 marksOct/Nov 25 · 31: 6 marksOct/Nov 25 · 32: 6 marksOct/Nov 25 · 33: 6 marksMay/Jun 26 · 31: 4 marksMay/Jun 26 · 32: 4 marksMay/Jun 26 · 33: 4 marks

    Assessment objectives

    • AO1 Knowledge & understanding
    • AO2 Apply & analyse
    • AO3 Design, program & evaluate
    • Describe44%
    • Outline30%
    • Explain26%
    • Complete22%
    Practise its 27 questionsBiggest: 8 marks · May/Jun 2022
  • 14.2Circuit switching and packet switching#8 of 14 on Paper 3Regular · 4354% next paper2.8 marks18/32 sittings↘ Oct/Nov 2025

    Set most sessions for a few marks; know the definition and one example.Syllabus: benefits, drawbacks and where each applies; the router's role in packet switching; how packets are passed across a network

    Next Paper 3
    54%
    5 in 10
    Marks a paper
    2.8
    4% of the paper · 45% of the topic
    Asked in
    18 / 32
    Paper 3 sittings · 20 questions
    Last asked
    Oct/Nov 2025
    9618/33 · Q3 · 4 marks · 1 series ago
    • Asked in 18 of 32 Paper 3 sittings — about 6 papers in 10.
    • About 2.8 marks a paper (4% of Paper 3; 45% of the topic's marks across its 2 bullets).
    • Last asked Oct/Nov 2025 · 9618/33 · Q3 (4 marks), 1 series ago.
    • Easing: 4.1 → 2.3 marks a paper.
    • Usually “Describe” or “State”: full sentences with a reason, not one-word answers.
    • Biggest chunk of marks so far: 8 in May/Jun 2022 · 9618/31 · Q3.
    • It is examined almost entirely as AO1 (Knowledge & understanding, 91%) — definitions and descriptions in syllabus words score.
    Last 12 sittings↘ Easing
    Oct/Nov 24 · 31: 5 marksOct/Nov 24 · 32: 7 marksOct/Nov 24 · 33: 5 marksMay/Jun 25 · 31: 4 marksMay/Jun 25 · 32: 4 marksMay/Jun 25 · 33: 4 marksOct/Nov 25 · 31: 4 marksOct/Nov 25 · 32: 4 marksOct/Nov 25 · 33: 4 marksMay/Jun 26 · 31: 0 marksMay/Jun 26 · 32: 0 marksMay/Jun 26 · 33: 0 marks

    Assessment objectives

    • AO1 Knowledge & understanding
    • AO2 Apply & analyse
    • AO3 Design, program & evaluate
    • Describe45%
    • State40%
    • Explain25%
    • Give25%
    Practise its 20 questionsBiggest: 8 marks · May/Jun 2022

3% of the topic's marks sit in question parts that belong to another topic (scenario questions cross sections) or that no bullet claims; they count for the topic, not for a bullet.

Marks a paper, year by year

212223242526

By exam series

  • May/Jun17/18 · 6.3 mk
  • Oct/Nov14/14 · 9.5 mk
Practise 42 real questions Smart Notes Quiz Flashcards Every topic on the Statometer

What you need to know2syllabus §14.1, §14.2

  1. 14.1Protocols — why protocols are essential; protocol stacks; the four-layer TCP/IP suite and what happens when a message crosses the internet; HTTP, FTP, POP3, IMAP, SMTP and BitTorrent
  2. 14.2Circuit switching and packet switching — benefits, drawbacks and where each applies; the router's role in packet switching; how packets are passed across a network

Video lectures11ZAK's YouTube channel · play here

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Open in the video library ZAK's channel

Infographics3draw these the way the examiner expects · download as PNG

Circuit switching vs packet switchingBoth get data from A to B across a network of routers. The difference is whether a path is reservedfirst.Circuit switchingAR1R2R3R4B1. A dedicated end-to-end path is set up before any data is sent.2. Every bit follows the same route, in order, at a guaranteed rate.3. The path is held (and paid for) until the call ends — even if idle.Used for: traditional telephone calls.Packet switchingAR1R2R3R4B1. Data is split into packets, each with a header (addresses, no.).2. Routers forward each packet independently — routes can differ.3. Packets may arrive out of order; re-ordered by packet number.Used for: the internet (IP), email, web, streaming.Circuit switchingPacket switchingSet-uppath reserved first (delay before start)none — send immediatelyReliability / orderguaranteed, in orderpackets can be lost or arrive out of orderEfficiencywastes capacity when idlelinks shared; copes with node failurecswithzak.com

Circuit vs packet switching

A2O Level
TCP/IP protocol stackData moves down the layers when sent (encapsulation) and up when received.ApplicationHTTP · HTTPS · FTP · SMTP · POP3 · IMAP · DNSuser services, dataTransportTCP (reliable, ordered) · UDP (fast, no guarantee)segments, portsInternetIP · routing between networkspackets, IP addressesLink (Network access)Ethernet · Wi-Fi · MAC addressesframes, physical mediasend ↓receive ↑Each layer adds its own header. TCP numbers segments and re-sends lost ones; IP just delivers packets best-effort.cswithzak.com

TCP/IP protocol stack

A2
Application-layer protocols & BitTorrentA protocol = agreed rules for communication. Name it, what it carries, and the direction: send = SMTP,receive = POP3/IMAP.ProtocolPurposeDetailHTTP/HTTPSrequest and deliver web pagesS = encrypted with TLS; GET / POSTFTPupload / download files to a serveranonymous or login; separate control + dataSMTPSEND email: client → server, server → serverpush protocol, port 25/587POP3RECEIVE: download mail, delete from serverone device; offline readingIMAPRECEIVE: mail stays on server, folders syncedmany devices; needs connectionThe journey of an emailSenderSender's mail serverRecipient's mail serverRecipientSMTPSMTPPOP3/IMAPBitTorrent — peer-to-peer file sharingTrackerwho has which piecesSeedPeerPeerLeechThe .torrent file points to a tracker. The swarm =all peers sharing the file, in pieces. A seed has thewhole file; a leech downloads without uploading.Pieces are downloaded from many peers at once, thenuploaded to others — the more peers, the faster.No central server; hard to shut down; used legallyfor Linux ISOs and illegally for copyrighted media.cswithzak.com

Application protocols & BitTorrent

A2

Browse all infographics →

Key terms13use these exact words in the exam

protocolTCP/IPapplication layertransport layerinternet layerlink layerHTTPFTPSMTPPOP3IMAPBitTorrentcircuit switching

Dotted terms are defined in the glossary.

Code help1referenced to the Cambridge pseudocode guide

Packet reassembly by sequence number

pseudocode §3, §7.1 Run in Playground
DECLARE Seq : ARRAY[1:4] OF INTEGER
DECLARE Payload : ARRAY[1:4] OF STRING
DECLARE Msg : STRING
DECLARE i, Want : INTEGER
Seq[1] ← 3
Payload[1] ← "ZAK"
Seq[2] ← 1
Payload[2] ← "CS "
Seq[3] ← 4
Payload[3] ← "!"
Seq[4] ← 2
Payload[4] ← "with "
Msg ← ""
FOR Want ← 1 TO 4
   FOR i ← 1 TO 4
      IF Seq[i] = Want THEN
         Msg ← Msg & Payload[i]
      ENDIF
   NEXT i
NEXT Want
OUTPUT Msg

Test yourself

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Every round is a fresh random draw, weak cards come back until you get them right, and past-paper questions come with their mark schemes. Marks earn XP on your dashboard.

Quiz: Communication & Internet Technologies (42)🃏 Flashcards: mix this topic (39)📶 Protocols & the TCP/IP stack (24)🔀 Circuit & packet switching, routing (15)Past-paper questions (42)🧅 TCP/IP layers & encapsulation📦 Packet vs circuit switching
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