What does 4.8 Communication and networking cover?

It covers serial and parallel transmission and synchronous versus asynchronous transmission with bit rate, baud rate and bandwidth, LANs and WANs and the star and bus topologies, wired and wireless networking including CSMA/CA and the SSID, the internet and packet switching with the TCP/IP four-layer model, IP addressing and DNS, network security with firewalls, encryption and digital certificates, and the client-server, peer-to-peer and web models.

Why is serial transmission used over long distances rather than parallel?

Parallel transmission sends several bits at once down multiple wires and is faster over short distances, but over longer distances the wires suffer from skew (bits arriving at slightly different times) and crosstalk, which corrupts data. Serial sends bits one at a time down a single line, avoiding these problems, so it is preferred for long-distance and modern high-speed links such as USB.

What are the four layers of the TCP/IP model?

The application layer holds protocols programs use such as HTTP and SMTP; the transport layer (TCP) splits data into numbered packets and ensures reliable, in-order delivery; the network or internet layer (IP) adds source and destination addresses and routes packets; and the link layer handles the physical transmission on the local network hardware such as Ethernet or Wi-Fi.

What is the difference between client-server and peer-to-peer?

In client-server, clients request services from a central server that holds resources and manages security, making management and backup centralised but creating a dependence on the server. In peer-to-peer, every device is an equal peer acting as both client and server and sharing resources directly, so there is no single point of failure and no costly server, but security and consistency are harder to manage.

How do digital certificates build trust online?

A digital certificate is issued by a trusted certificate authority and binds a public key to an identity, so when you connect to a website you can trust that its public key really belongs to that organisation. This underpins HTTPS. A digital signature is different: it proves a message came from the claimed sender and was not altered, by signing a hash with the sender's private key.

EnglandComputer Science

AQA A-Level Computer Science 4.8 Communication and networking: transmission, networks, TCP/IP, security and the web

A deep-dive AQA A-Level Computer Science guide to 4.8 Communication and networking. Covers serial and parallel transmission, LANs, WANs and topologies, wireless networking, the internet and the TCP/IP model, network security and encryption, and the client-server, peer-to-peer and web models.

Generated by Claude Opus 4.818 min read4.8Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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What 4.8 actually demands
Transmission methods
Networks, topologies and wireless
The internet and TCP/IP
Security and the web
Check your knowledge

What 4.8 actually demands

This module is how computers talk to each other. AQA expects you to explain how data is transmitted, the types of network and topology, how the internet and TCP/IP work, how networks are secured, and the client-server, peer-to-peer and web models.

Transmission methods

Serial sends bits one at a time; parallel sends several at once but suffers skew over distance, so serial is used for long-distance links. Synchronous transmission shares a clock; asynchronous frames each byte with start and stop bits. Know bit rate (bits per second), baud rate (signal changes per second) and bandwidth (the frequency range that limits bit rate).

Networks, topologies and wireless

A LAN is local and owner-controlled; a WAN spans a large area using third-party infrastructure. A star topology centres on a switch; a bus shares one backbone cable. Wireless networks use an SSID to identify the network and CSMA/CA to avoid collisions on the shared radio channel.

The internet and TCP/IP

The internet is a network of networks using packet switching: data is split into independently routed packets and reassembled. The TCP/IP model has four layers (application, transport, network, link). Every device has an IP address, and DNS maps domain names to IP addresses; routers forward packets and gateways join networks using different protocols.

Security and the web

Firewalls filter traffic and proxy servers sit between clients and the internet. Encryption (symmetric shared key, or asymmetric public/private keys) protects data; digital signatures prove origin and integrity and digital certificates verify public keys. On the web, a browser requests pages from a web server built from HTML, CSS and JavaScript, and clients can be thin or thick.

Check your knowledge

State one reason serial transmission is preferred to parallel over long distances. (1 mark)
State the difference between bit rate and baud rate. (2 marks)
State the difference between a LAN and a WAN. (2 marks)
State why wireless networks use CSMA/CA. (2 marks)
Explain what packet switching is. (2 marks)
State the purpose of DNS. (1 mark)
State the purpose of a firewall. (2 marks)
State one advantage of the client-server model over peer-to-peer. (1 mark)

Solutions

Q1: Parallel transmission suffers from skew over distance (bits arriving out of step), so serial is more reliable over long distances.
Q2: Bit rate is the number of bits transmitted per second; baud rate is the number of signal changes per second, and each change can carry more than one bit.
Q3: A LAN covers a small area with owner-controlled hardware; a WAN covers a large geographic area, usually using third-party infrastructure.
Q4: Devices share a radio channel and cannot reliably detect collisions, so they avoid them by checking the channel is clear before transmitting.
Q5: Data is split into packets, each carrying source and destination addresses and routed independently across the network, then reassembled in order at the destination.
Q6: It translates human-readable domain names into the IP addresses used to locate devices.
Q7: It controls traffic between networks against a set of rules, blocking unauthorised or unwanted packets.
Q8: Centralised management, backup and security are easier because resources are held on the server.

Sources & how we know this

AQA A-level Computer Science (7517) specification — AQA (2015)