Fundamentals of computer networks: free AQA GCSE Computer Science practice questions

Mistakes to avoid

Most of these mix up two things that section 3.5 keeps apart.

• Confusing a MAC address with IP. A MAC address is the physical address embedded in a device's network adapter. IP is a protocol, not an address: it works at the internet layer, which addresses and packages data for transmission and routes the packets across the network.
• Saying HTTPS stops hackers. It encrypts data in transit so intercepted traffic cannot be read. It does nothing about a weak password or malware on your machine.
• Confusing SMTP with IMAP. SMTP sends email. IMAP retrieves it from the server while leaving it there, so every device shows the same mailbox.
• Saying wireless is always slower than wired. It is usually slower, and distance, obstacles and interference can reduce its performance further.
• Mixing up the layers of the TCP/IP model. HTTP, HTTPS, SMTP and IMAP work at the application layer, TCP at the transport layer and IP at the internet layer.
• Treating MAC address filtering as encryption. Filtering decides which devices may join the network. Encryption stops intercepted data from being read.

What a network is and what it costs

A network is two or more computers connected so they can share data and resources. The benefits are sharing files, sharing hardware such as printers, central backup and central management of software and users. The costs are the equipment and cabling, the need for someone to manage it, and the fact that one attack or one failure can reach many machines at once. A LAN usually covers a relatively small geographical area, such as one site, and is often owned and managed by one person or organisation. A WAN usually covers a wide geographic area and is often under collective or distributed ownership. The Internet is the biggest example of a WAN.

Wired against wireless

Wired connections use copper or fibre optic cable. They are usually faster and more reliable than wireless, and they are generally harder to intercept, because there is no radio signal to pick up. Wireless is usually more convenient and often cheaper to install in an existing building, but its performance is more affected by distance, obstacles and interference, and its signal can be picked up by anyone within range.

Protocols and layering

A protocol is an agreed set of rules for how devices communicate. Without shared protocols, devices from different manufacturers could not talk to each other. The TCP/IP model has four layers. The application layer is where network applications such as web browsers and email programs operate, and HTTP, HTTPS, SMTP and IMAP work there. The transport layer, where TCP works, sets up communication between the two hosts. The internet layer, where IP works, addresses and packages data for transmission and routes the packets across the network. The link layer is where the network hardware, such as the network interface card, is located.

The protocols you have to name

HTTP transfers web pages. HTTPS is HTTP with encryption, so data sent to and from the site cannot be read if it is intercepted. SMTP sends email. IMAP retrieves email from a server while leaving it there, so the same mailbox looks the same on every device. Encryption on a network scrambles data so that anyone intercepting it cannot read it without the key. On wireless networks that is essential, because the signal is available to anyone in range.

Addresses and hardware

A MAC address is the physical address embedded in a device's network adapter, and MAC address filtering uses it to let a device onto a network or block it. IP works at the internet layer, which addresses and packages data for transmission and routes the packets across the network. A network interface card connects a device to a network and sits at the link layer, where the network hardware is.