How do IP addresses identify devices, and why do networks need agreed protocols?
Explain the purpose of IP addresses and protocols, describe how data is sent in packets, and give examples of common protocols
A focused answer to the O-Level Computing point on addressing and protocols. The purpose of an IP address, what a protocol is and why networks need agreed rules, how data travels in packets, and examples of common protocols.
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What this dot point is asking
SEAB wants you to explain why devices need IP addresses, what a protocol is and why networks need agreed rules, how data travels in packets, and to give examples of common protocols. The central idea is that for any two devices to communicate, each must be uniquely addressed and both must follow the same rules, and that data is broken into small packets to travel efficiently.
The answer
IP addresses
An IP address (Internet Protocol address) is a unique number that identifies a device on a network. It works like a postal address: data is labelled with the destination IP address so the network can deliver it to the correct device, and with the source address so a reply can come back.
example IPv4 address: 192.168.1.10
Without unique addresses, the network would not know where to send data.
What a protocol is
A protocol is an agreed set of rules for how data is formatted and transmitted between devices. Both sides follow the same rules, so a device made by one manufacturer can talk to a device made by another. Protocols cover things like how to split data, how to address it, how to send it, and how to check it arrived correctly.
Why networks need protocols
If every device used its own rules, none could understand the others. Agreed protocols are like a shared language: they let billions of different devices communicate reliably and consistently.
Sending data in packets
Large messages are not sent in one piece. They are split into small packets. Each packet carries:
- a header with control information (the destination IP address, the source IP address, and a packet number for reassembly),
- the data itself (a chunk of the message).
At the destination, the packets are put back in order using their numbers to rebuild the original message.
Advantages of packets
- If one packet is lost, only that small packet is resent, not the whole message.
- Packets can take different routes, balancing traffic and avoiding broken links.
Common protocols
| Protocol | Used for |
|---|---|
| HTTP / HTTPS | requesting and sending web pages (HTTPS is encrypted) |
| TCP/IP | splitting data into packets and addressing and delivering them |
| SMTP | sending email |
Examples in context
Example 1. Streaming a video. A video is delivered as a stream of packets addressed to your device's IP. If a packet is lost on a busy network, only that tiny packet is resent, so the video keeps playing rather than restarting, which is the packet advantage in action.
Example 2. Devices from different makers. A phone, a laptop and a smart speaker from different companies all share one home network because they follow the same protocols. The shared rules act as a common language, letting very different devices talk to the router and each other.
Try this
Q1. State what an IP address is used for. [2 marks]
- Cue. It uniquely identifies a device on a network so data can be delivered to and from the correct device.
Q2. State two items found in a packet header. [2 marks]
- Cue. The destination IP address, the source IP address, and a packet number for reassembly (any two).
Q3. Explain why networks need agreed protocols. [2 marks]
- Cue. So that different devices follow the same rules for sending data and can therefore communicate reliably with each other.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original4 marks(a) State the purpose of an IP address. (b) Explain what a protocol is and why networks need agreed protocols.Show worked answer →
(a) An IP address is a unique number that identifies a device on a network, so that data can be sent to and from the correct device. It works like a postal address for a computer.
(b) A protocol is an agreed set of rules for how data is formatted and transmitted between devices. Networks need protocols so that different devices, made by different manufacturers, can communicate reliably: both sides follow the same rules for splitting, addressing, sending and checking data, so the message is understood correctly.
Markers reward an IP address uniquely identifying a device for correct delivery, and a protocol as agreed rules that let different devices communicate consistently.
Original5 marksData sent across the internet is split into packets. (a) State two pieces of information a packet header contains. (b) Explain one advantage of sending data in packets rather than as one large block.Show worked answer →
(a) A packet header contains control information such as: the destination IP address (where it is going), the source IP address (where it came from), and a packet number so the parts can be reassembled in the right order. Any two are acceptable.
(b) An advantage of packets: if one packet is lost or corrupted, only that small packet needs to be resent rather than the whole message; and packets can take different routes across the network, so traffic is balanced and a single congested or broken link does not stop everything. Either advantage is acceptable.
Markers reward two valid header fields (such as destination and source addresses, or a sequence number) and one genuine advantage of packets such as easy resending or flexible routing.
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