1.3.2 Wired and wireless networks, protocols and layers — OCR GCSE Computer Science revision notes

Modes of connection

Figure: Wired against wireless

	Wired (Ethernet)	Wireless (Wi-Fi, Bluetooth)
Speed	Generally faster	Generally slower
Reliability	More reliable — not affected by interference	Affected by distance, walls and other devices
Security	More secure — physical access to the cable is needed	Signals travel through the air and can be intercepted
Convenience	Devices are tethered to a cable	Devices can move freely; no cabling to install
Cost	Cabling is expensive to install, especially in an existing building	Cheaper to set up; only access points are needed
Number of devices	Limited by the number of ports	Many devices can connect, though they share bandwidth

Bluetooth differs from Wi-Fi in range and purpose: short range, low power, for connecting a few devices directly — headphones, a keyboard — rather than joining a network.

You should be able to recommend one or more connections for a given scenario. The reasoning is usually: wired where speed, reliability and security matter and the device does not move — a desktop, a server, a games console. Wireless where mobility matters or cabling is impractical — phones, tablets, laptops, or a listed building where cables cannot be run.

Understanding how Ethernet, Wi-Fi and Bluetooth actually work is not required.

Encryption, addressing and standards

Encryption scrambles data before it is sent, so that anyone intercepting it cannot read it. Only a device with the correct key can decrypt it back into readable form. The principle is that the data is still intercepted — encryption does not prevent that — but what the interceptor gets is meaningless.

That matters most on wireless connections, where signals travel through the air and cannot be physically protected.

Figure: IP and MAC addresses

	IP address	MAC address
What it identifies	A device's location on a network	The specific piece of hardware — the NIC
Assigned by	The network, and it changes when the device joins a different network	The manufacturer, permanently, when the NIC is made
Format — IPv4	Four numbers 0–255 separated by dots, e.g. 192.168.1.14	Twelve hexadecimal digits, usually in six pairs separated by colons or dashes
Format — IPv6	Eight groups of four hexadecimal digits separated by colons	—
Used for	Routing data across networks, including the internet	Identifying devices within a local network

IPv6 exists because IPv4 has only about 4 billion possible addresses, which is no longer enough for the number of connected devices.

Standards are agreed rules covering an area of computing, so that hardware and software from different manufacturers can work together. Without them, a printer from one company might not work with a computer from another, and a file saved in one program could not be opened in a different one.

Knowledge of individual standards is not required — only the principle of what a standard is for.

Encryption: scrambling data before it is sent so that anyone intercepting it cannot read it; only a device with the correct key can decrypt it

Common protocols

A protocol is a set of rules for transferring data. Both ends of a communication must follow the same rules, or neither can make sense of what the other sends.

Different protocols exist because they do different jobs — sending a web page, transferring a file and delivering email have different requirements.

Figure: The protocols named in the specification

Protocol	Purpose and key features
TCP/IP	Transmission Control Protocol / Internet Protocol — the underlying rules for internet communication. TCP splits data into packets and reassembles them in order at the other end; IP handles addressing and routing
HTTP	Hyper Text Transfer Protocol — transfers web pages between a web server and a browser
HTTPS	The same as HTTP but encrypted, so data such as passwords and card details cannot be read if intercepted
FTP	File Transfer Protocol — used for sending and receiving files between computers
POP	Post Office Protocol — retrieves email from a server, and traditionally deletes it from the server once downloaded
IMAP	Internet Message Access Protocol — retrieves email while leaving it on the server, so it can be read from several devices
SMTP	Simple Mail Transfer Protocol — sends email, and transfers it between mail servers

The three email protocols split by direction: SMTP sends, POP and IMAP receive — and IMAP is the one that keeps mail on the server.

Protocol: a set of rules for transferring data, which both ends of a communication must follow

The concept of layers

Layers divide network communication into separate levels, each handling one part of the job and passing its result to the next. A protocol operates at one layer and does not need to know how the others work.

The benefits of using layers, which is what is actually examined:

• Each layer can be developed and changed independently, without rewriting the others. • Problems can be isolated to one layer, making faults far easier to find and fix. • Different manufacturers can work on different layers, provided each follows the agreed rules. • It breaks a complicated process into manageable parts. • Hardware and software from different sources can interoperate, because each only has to meet the interface of the layer above and below.

The specification uses the 4-layer TCP/IP model as a teaching example — but note that knowledge of the names and function of each TCP/IP layer is explicitly not required. You need to understand why layering is useful, not to memorise the four layers. That is a genuine saving of revision time, so it is worth knowing.

Worked example

A shopping website changes from HTTP to HTTPS. Explain what this changes and why it matters.

Identify the difference: HTTPS is HTTP with encryption added.
State what encryption does: the data is scrambled before transmission and can only be read with the correct key.
Identify what is at risk on a shopping site: passwords, addresses and payment card details.
Explain the consequence of interception without it: readable personal and financial data.
Note what does not change, so the answer is precise.

Answer: HTTPS encrypts the data sent between browser and server, so if it is intercepted it cannot be read. On a shopping site that protects passwords and card details. The data can still be intercepted — encryption does not prevent that — but what an attacker obtains is meaningless without the key.

Common mistake

An IP address identifies where a device is on a network and changes when it joins a different one; a MAC address identifies the hardware itself and never changes. Questions frequently test exactly this distinction.

Layers: the division of network communication into separate levels, each handling one part of the job and passing its result to the next, so each can be developed and changed independently

Before you practise

Wired is faster, more reliable and more secure; wireless is more convenient and cheaper to install.
Encryption scrambles data so an interceptor cannot read it — it does not prevent interception.
IP addresses identify a location on a network and change; MAC addresses identify hardware and are permanent.
IPv4 is four numbers 0–255; IPv6 is eight groups of four hex digits; MAC addresses are twelve hex digits.
Standards are agreed rules letting hardware and software from different manufacturers work together.
A protocol is a set of rules for transferring data; both ends must follow the same one.
TCP/IP underlies internet communication; HTTP and HTTPS carry web pages; FTP transfers files; SMTP sends email; POP and IMAP receive it.
Layers divide communication into independent levels, making development, fault-finding and interoperability easier.
The names and functions of the four TCP/IP layers are NOT required — only the benefits of layering.

Modes of connection

Encryption, addressing and standards

Common protocols

The concept of layers

Before you practise

Now practise it