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IB Computer Science A2.1: Network fundamentals

New IB Computer Science syllabus · first exams May 2027 · Theme A · SL & HL (A2.1.5 HL only)

Guiding question: What are the principles and concepts that underpin how networks operate?

A2.1 is the first sub-unit of A2 Networks (11 hours SL, 18 hours HL). It covers how computers communicate: network types, digital infrastructure, devices, protocols and, at HL, the TCP/IP model.

StatementTopicCommand term
A2.1.1Purpose and characteristics of networksDescribe
A2.1.2Modern digital infrastructuresDescribe
A2.1.3Function of network devicesDescribe
A2.1.4Transport and application protocolsDescribe
A2.1.5 (HL)The TCP/IP modelDescribe

Key points

A2.1.1 Types of network

  • LAN: a small area, such as one building. Fast, and owned by the organisation.
  • WAN: a large geographic area, such as the internet. Slower, with higher latency, and uses leased infrastructure.
  • PAN: about 10 m around one person, using Bluetooth or NFC (for example a phone, earbuds and smartwatch).
  • VPN: an encrypted tunnel across a public network that makes a remote user appear to be on site. It is a logical network, not a physical one.

A2.1.2 Digital infrastructure

  • The internet: universal access, but security risks.
  • Cloud computing: scalable and low upfront cost, but vendor lock-in, latency and privacy concerns.
  • Distributed systems (such as blockchain): no single point of failure, but complex to synchronise.
  • Edge computing: processing near the source gives low latency, but limited local power.
  • Mobile networks: connectivity everywhere, at a high infrastructure cost.

The IB's own examples: the worldwide web (built on the internet), cryptocurrency blockchains (distributed systems), smart traffic lights (edge computing) and a school (cloud computing).

A2.1.3 Network devices

  • NIC: connects a device to a network; has a unique MAC address.
  • Switch: connects devices within a LAN, using MAC addresses.
  • Router: forwards packets between networks, using IP addresses and a routing table.
  • Wireless access point: extends a wired LAN over Wi-Fi.
  • Modem: converts between digital signals and the ISP's signal.
  • Hardware firewall: filters traffic by rules.
  • Gateway: translates between different protocols.

The guide also requires you to map devices to the TCP/IP model: NICs, switches, access points and modems work at the Network Interface layer, and routers at the Internet layer.

A2.1.4 Protocols

  • TCP: reliable and ordered. It sets up a connection, acknowledges packets and resends lost ones. Used for web, email and file transfer.
  • UDP: fast, with no acknowledgement, so packets may be lost or arrive out of order. Used for streaming, gaming and voice calls.
  • HTTP / HTTPS: web pages. HTTPS adds TLS encryption and uses port 443.
  • DHCP: automatically assigns IP addresses in four steps: Discover → Offer → Request → Acknowledge.

A2.1.5 The TCP/IP model (HL only)

LayerProtocolsWhat it adds
ApplicationHTTP(S), DHCP, DNSThe data itself
TransportTCP, UDPPort numbers: the data becomes segments
InternetIPIP addresses: segments become packets
Network InterfaceEthernet, Wi-FiMAC addresses: packets become frames, then signals

Each layer adds a header as data goes down the stack when sending (encapsulation) and removes it as data goes up when receiving.

Exam-style question

Explain why an online video streaming service would use UDP rather than TCP. [3]

Mark scheme

Award [1] for each point, up to [3]:

  • UDP does not require acknowledgement of each packet, which reduces overhead and latency;
  • A few lost packets only cause a brief glitch, which is acceptable for video, whereas TCP retransmission would cause buffering or freezing;
  • Continuous delivery matters more than perfect accuracy for streaming;

Common mistakes that cost marks

  • Confusing switches and routers. A switch works within a LAN using MAC addresses. A router works between networks using IP addresses.
  • Calling a VPN a physical network. It is an encrypted tunnel over an existing network.
  • Saying UDP is "unreliable, so it's bad". Explain why speed matters more than accuracy in the given scenario.

Frequently asked questions

Is the TCP/IP model on the SL syllabus?
A2.1.5 (the TCP/IP model) is HL only. However, A2.1.3, which all students study, asks how devices map to the layers of the TCP/IP model.

Which protocols do I need for A2.1.4?
TCP, UDP, HTTP, HTTPS and DHCP.

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