Cambridge A Level Information Technology (ICT): Communications technology (9626)

This guide teaches topic 14, Communications technology, of the Cambridge International AS & A Level Information Technology 9626 syllabus for examination in 2025, 2026 and 2027 (version 3), sections 14.1 to 14.10. It is A Level only, assessed in Paper 3 Advanced Theory (no calculator).

See the revision notes, the practice set, the course hub, the printable checklist and the diagnostics. Encryption and TLS/SSL were met at AS in topic 1, and malware in eSecurity.

What this topic covers

Section	Key content
14.1 Networks	Network types, topologies, uses, pros and cons
14.2 Components	Role and operation of NICs, hubs, switches, routers and others
14.3 Servers	Server types, request and response, server farms
14.4 Cloud computing	Shared resources, uses, pros and cons
14.5 Data transmission	Bandwidth, bit rate, streaming, transmission media
14.6 Protocols	Named protocols, switching, addressing, routing, layering, firewalls
14.7 Wireless	Methods, operation, uses, security
14.8 Mobile systems	Cellular networks, satellite systems
14.9 Network security	Threats, impacts, prevention
14.10 Disaster recovery	Risk identification, control, minimising risk

14.1 Networks

• LAN: devices on one site, owned by one organisation.
• WAN: networks linked over a wide area, usually through leased lines or the internet.
• Client-server: a central server holds files, security and services; clients request them. Easy to secure and back up centrally, but the server is a single point of failure.
• Peer-to-peer (P2P): every computer is equal and shares its own resources. Cheap, but no central back-up or security.
• VPN: a private, encrypted link across a public network, made by tunnelling (wrapping one packet inside another). Home workers reach the office LAN as if on site.
• Mobile networks: cellular voice and data for phones (14.8).

Characteristics. Physical topology is how devices are cabled; logical topology is how data flows. A star cabled round a hub is physically a star but logically a bus, because the hub sends every signal to every device. Architecture means client-server or P2P. Protocols differ by type: Ethernet or Wi-Fi in a LAN, IP across a WAN, tunnelling protocols in a VPN.

Uses: sharing and storing resources, sharing peripherals, exchanging data, internet services, telephony, tunnelling, and content delivery (streaming, software downloads). BitTorrent splits a large file into pieces; you download pieces from many peers at once while uploading pieces you hold, so no single server carries the load.

14.2 Components in a network

Component	Role and operation
NIC	Connects a device to a cabled network; holds its MAC address
Wireless NIC	Same job by radio, through an aerial
Repeater	Regenerates a weakened signal so it travels further
Hub	Sends incoming data out of every port; cannot read addresses
Switch	Learns which MAC address is on each port; sends each frame only to its destination port
Wireless access point	Connects wireless devices to a cabled LAN
Bridge	Joins two LAN segments using the same protocol; filters by MAC address
Router	Forwards packets between networks using IP addresses and a routing table
Gateway	Joins networks using different protocols, converting between them

Working together: PCs’ NICs cable to a switch; a WAP on the switch serves laptops; the switch connects to a router, which forwards outside traffic to the internet provider. Switches cut collisions and improve security compared with hubs, as frames are not broadcast.

14.3 Network servers

File (central storage with access rights), web (sends pages to browsers), mail (sends, receives, stores email), applications (runs software for clients), print (manages print queues), FTP (files for upload and download), proxy (sits between clients and the internet; filters content, caches pages, hides internal addresses) and virtual (a software server; several share one physical machine, saving hardware, but one hardware fault stops them all).

Servers use request and response: a client sends a request, the server processes it and replies. A server farm is a large group of servers. A load balancer shares requests between them, so heavy demand is handled and a failed server’s work moves to another. They need much power.

14.4 Cloud computing

Cloud computing uses shared computing resources (storage, processing, software) owned by a provider and reached over the internet; customers pay for use. Individuals store and sync photos and files and use online office software. Organisations host websites and databases, back up off site and collaborate on documents.

Advantages: no hardware to buy, capacity grows on demand, access from anywhere, provider handles maintenance. Disadvantages: needs reliable internet, ongoing fees, less control over where data is held, security depends on the provider.

14.5 Data transmission across networks

Bandwidth is the maximum rate a link can carry data, in bits per second (in signal terms, the range of frequencies a channel carries, in hertz). Bit rate is the number of bits actually sent per second, or that a media stream needs per second of playback. Bandwidth is capacity; bit rate is demand.

Streaming. A real-time stream (a live match) is sent as it happens. An on-demand stream (a stored film) plays when you choose. If available bandwidth is below the stream’s bit rate, the player buffers or switches to a lower-quality version. UHD TV needs a far higher bit rate than standard definition, so relies on high-bandwidth media and compression.

Medium	Properties	Typical use
Fibre optic	Light pulses; highest bandwidth; long distances; immune to electrical interference; costly	Backbones, links to buildings
Twisted pair	Cheap; bandwidth falls with distance; interference	Ethernet LANs
Coaxial	Shielded, so less interference than twisted pair; bulkier	Cable TV and broadband
Laser	Beam through air; needs line of sight; affected by fog	Links between nearby buildings

Worked example 1

A home has a 50 Mbit/s connection. Two UHD films stream at 20 Mbit/s each and a video call uses 4 Mbit/s. Can a third film be added? How long would a 1.5 GB download take on an idle line? (1 GB = 1000 MB.)

1. Demand now: 2 × 20 + 4 = 44 Mbit/s, below 50.
2. With a third film: 3 × 20 + 4 = 64 Mbit/s, above 50, so it will buffer or drop quality.
3. 1.5 GB = 1500 MB = 1500 × 8 = 12 000 Mbit.
4. Time = 12 000 ÷ 50 = 240 s (4 minutes).

14.6 Network protocols

A protocol is an agreed set of rules for formatting, addressing, sending and receiving data. Without them, different makers’ devices could not communicate.

Protocol	Purpose
TCP	Sets up a connection, numbers segments, acknowledges and resends lost data
IP	Addresses and routes packets between networks
ICMP	Error and status messages; used by ping
ARP / InARP	ARP finds a MAC address from an IP address; InARP finds an IP address from a link-layer address
DHCP	Assigns IP addresses and settings automatically
UDP	Datagrams with no connection or acknowledgement; fast, for live media
HTTP / HTTPS	Web pages; HTTPS encrypts with TLS
FTP	File upload and download
Tunnelling (L2TP)	Carries packets inside other packets for VPNs; often paired with IPsec
SMTP	Sends email
POP3	Downloads email to one device, usually removing it from the server
IMAP	Keeps email on the server; devices stay in sync
Telnet / SSH	Remote command line; Telnet unencrypted, SSH encrypted
IPsec	Encrypts and authenticates IP packets
TLS/SSL	Encrypts a client-server session

Packet switching. Data is split into packets, each with a header (source and destination addresses, sequence number), a payload and usually a trailer (error check). Packets may take different routes and are reassembled. Connection mode (frame relay, TCP) sets up a connection first, giving reliable, ordered delivery. Connectionless (datagram) mode (Ethernet, IP, UDP) sends each packet independently: faster, not guaranteed.

Circuit switching reserves a dedicated channel for the whole session, as in a traditional phone call. Message switching sends the whole message node to node; each stores it and forwards it when the next link is free.

Addressing. A MAC address is a 48-bit physical address on a NIC, used within a local network. An IP address is a logical address for routing between networks: IPv4 is 32 bits (four denary numbers, e.g. 192.168.1.20); IPv6 is 128 bits (eight groups of hexadecimal), introduced because IPv4 addresses were running out.

Routing. Routers choose paths from routing tables. Static routing: routes entered by hand; predictable and secure, but cannot adapt to a failed link. Dynamic routing: routers share information and update tables automatically; adapts to failures but uses bandwidth and processing. Interior gateway protocols route within one autonomous system; exterior gateway protocols route between autonomous systems; the Border Gateway Protocol does this across the internet.

Layering. OSI has seven layers: physical, data link, network, transport, session, presentation, application. TCP/IP has four: link, internet, transport, application. TCP/IP is the internet’s working model; OSI is a more detailed reference model. TCP/IP’s application layer spans OSI’s top three layers; its link layer spans the bottom two.

Firewalls allow or block packets by rules on IP address, port, protocol and direction. A secure configuration blocks everything by default and opens only what is needed.

Worked example 2

A doctor wants one inbox on phone and laptop. Choose protocols.

• Send with SMTP.
• Receive with IMAP, which keeps mail on the server so both devices match; POP3 would move each message onto one device.
• Run both over TLS for encryption.

14.7 Wireless technology

Wi-Fi (radio, medium range, wireless LANs, IEEE 802.11 protocols); Bluetooth (low-power radio over a few metres, devices pair first); infrared (line of sight, remote controls); microwave (line-of-sight links between masts, satellite links); radio (broadcast to many receivers); NFC (devices almost touching; contactless payment).

Wireless power transfer charges without a cable, for example on an inductive pad. Uses: data exchange, mobile communications and the Internet of Things.

Security. Signals can be intercepted outside the building. Use WPA2 or WPA3 (WEP is weak), a strong passphrase, changed default router passwords and updated firmware.

Pros: mobility, no cabling. Cons: slower than cable, interference, limited range, interception.

14.8 Mobile communication systems

A cellular network divides an area into cells, each with a base station. Neighbouring cells use different frequencies so frequencies can be reused further away. Moving between cells, sessions are handed over between base stations. 3G brought mobile internet; 4G faster all-IP data; 5G higher speeds, lower delay and many more devices, suiting IoT.

Satellites. Data is encoded and modulated, sent from a ground station on the uplink, amplified by the satellite’s transponder and returned on a downlink at a different frequency. Uses: GPS (position from the timing of signals from several satellites), global mapping from images, surveillance, broadcasting TV and radio including UHD TV, and telephones in remote areas.

14.9 Network security

Threats: brute force (trying many passwords), denial of service (flooding a server), botnets (infected machines controlled together), malware, malicious actors, SQL injection (database code typed into a web form) and poor network policies. Impacts: data destruction; manipulation, modification or theft; identity theft.

Prevention: barriers, locks, surveillance, alarms, guards; biometrics; anti-malware, anti-virus and anti-spyware; encryption; access rights; firewalls blocking unneeded ports. Drawbacks: biometrics are costly, anti-virus needs constant updates, stolen keys defeat encryption.

14.10 Disaster recovery management

Threats: natural disasters, equipment and power failures, cybercrime, malware, criminal activity, accidents. Risk analysis lists what could go wrong; perpetrator analysis asks who might attack and why; risk testing simulates a disaster to test the plan; quantifying the risk scores each one, often likelihood × impact.

Control: detect threats early, prevent them, and restore from back-ups using a tested plan. Strategies: UPS and surge protection, passwords and access controls, anti-malware, and regular back-ups kept off site.

Worked example 3

Risks scored 1 to 5. Power cut: likelihood 4, impact 3. Flood: 1, 5. Ransomware: 3, 5.

1. Scores: 4 × 3 = 12; 1 × 5 = 5; 3 × 5 = 15.
2. Priority: ransomware, then power cut, then flood.

Common errors

• Confusing a switch (MAC addresses, within a LAN) with a router (IP addresses, between networks).
• Treating bandwidth and bit rate as the same.
• Calling UDP unreliable without saying why: no acknowledgement or resending.

Official syllabus

Cambridge International AS & A Level Information Technology 9626, syllabus for examination in 2025, 2026 and 2027 (version 3), Cambridge University Press & Assessment: topic 14, Communications technology, sections 14.1 to 14.10.