Examhaus — Achieve with confidence.

IB Computer Science A2.2: Network architecture

New IB Computer Science syllabus · first exams May 2027 · Theme A · SL & HL (A2.2.2 HL only)

A2.2 is about how networks are structured: how devices are arranged, what servers do, how networking models differ, and how networks are divided up for performance and security.

StatementTopicCommand term
A2.2.1Network topologiesDescribe
A2.2.2 (HL)Function of serversDescribe
A2.2.3Networking modelsCompare and contrast
A2.2.4Network segmentationExplain
⚠️ Command term alert: A2.2.3 uses Compare and contrast. Give both similarities and differences, point by point, not two separate descriptions.

Key points

A2.2.1 Topologies: star, mesh and hybrid

Judge every topology on the five factors the guide lists: reliability, transmission speed, scalability, data collisions and cost.

FactorStarFull meshHybrid (star-mesh)
ReliabilityOne device failing doesn't matter, but the central switch is a single point of failureNo single point of failureResilient backbone with isolated segments
ScalabilityEasy, up to the number of switch portsVery hard: n(n−1)/2 linksEasy: add new star segments
CostModerateVery highHigh, but justified at enterprise scale
Typical useHomes, offices, schoolsInternet backbone, critical systemsCorporations, campuses, government

A2.2.2 Servers (HL only)

  • Web server: responds to HTTP(S) requests.
  • File server: stores shared files.
  • Mail server: sends email with SMTP and delivers it with IMAP or POP3.
  • DNS server: converts domain names into IP addresses.
  • DHCP server: assigns IP settings automatically.
  • Proxy server: sits between users and the internet; caches and filters content and hides client IP addresses.

Evaluate each one on function, scalability, reliability and security.

A2.2.3 Client-server vs peer-to-peer

  • Client-server: a dedicated server provides the services and clients request them. It centralises security, backups and control, but costs more, and the server can be a single point of failure. Examples: web browsing, email, online banking, a school learning platform.
  • Peer-to-peer: every device is both a client and a server. It's cheap and easy to set up, with no central point of failure, but security and backups are harder to manage. Examples: BitTorrent, blockchain, small home networks.

A2.2.4 Network segmentation

Segmentation divides a network into smaller parts to reduce congestion, improve performance and security, and manage resources efficiently.

  • Subnetting: splits an IP network into smaller subnets with smaller broadcast domains. Traffic between subnets passes through a router, which can enforce access rules.
  • VLANs: separate devices logically, for example staff and guest Wi-Fi, without separate physical switches.

Exam-style question

Explain why a hospital might use VLANs rather than separate physical networks for its staff and patient Wi-Fi. [4]

Mark scheme

Award [1] for each point, up to [4]:

  • VLANs separate traffic logically without needing separate physical switches;
  • This reduces hardware cost while still isolating staff and patient traffic;
  • Patient devices on a separate VLAN cannot access confidential medical systems;
  • Traffic within each VLAN is isolated, reducing the risk from compromised devices;
  • Broadcast domains are smaller, improving network performance;

Common mistakes that cost marks

  • Ignoring the scenario. A hospital that values reliability needs a mesh or hybrid topology; a home user focused on cost needs a star.
  • Missing the five topology factors. Use reliability, speed, scalability, collisions and cost.
  • Treating "compare and contrast" as two separate descriptions. Write direct comparisons, using words like "whereas".

Frequently asked questions

Which topologies do I need to know?
Star, mesh and hybrid.

Do I need to know subnetting and VLANs?
Yes. The guide says network segmentation must include segmenting, subnetting and VLANs.

Go further