3.5 - Network protocols and TCP/IP layers
Devices need agreed rules to communicate. Learn the purposes of the six required protocols and how their jobs fit into the application, transport, internet and link layers of TCP/IP.
What protocols agree
Connecting devices is not enough if each interprets messages differently.
Network protocol
A set of agreed rules governing communication between devices on a network.
Rules can specify message formats, addressing and how devices respond. Imagine one computer sends a request for a page, but the receiver treats the request as an email instruction. Their physical connection works, yet the communication fails because they do not follow the same rules for that task. Shared protocols let software and devices from different manufacturers interpret each other's messages.
Different protocols solve different problems. A browser needs rules for requesting a page; a network needs rules for addressing and routing the data that carries that request. One communication can use several protocols together, each handling its own job.
TCP, IP, HTTP, HTTPS, SMTP and IMAP
Choose a protocol by the job it performs, and explain that job in the communication being described.
| Protocol | Purpose |
|---|---|
| TCP — Transmission Control Protocol | Establishes communication between hosts and provides reliable, ordered delivery. It can detect missing data and arrange retransmission. |
| IP — Internet Protocol | Addresses data packets and supports routing them towards their destination across networks. |
| HTTP — Hypertext Transfer Protocol | Governs requests and responses for web resources, such as a browser requesting a web page. |
| HTTPS — Hypertext Transfer Protocol Secure | Provides encrypted HTTP communication, protecting web transactions against reading or alteration in transit. |
| SMTP — Simple Mail Transfer Protocol | Sends email, including sending it from a client to a mail server and transferring it between mail servers. |
| IMAP — Internet Message Access Protocol | Lets a mail client access and manage messages held on a mail server; messages can stay on the server and be accessed from different devices. |
Web example. A pupil opens the school's website. HTTP supplies the web request/response rules. With HTTPS, that exchange is encrypted, which matters if the pupil sends account details. IP supplies addressing and routing, while TCP helps deliver the data reliably and in order. HTTPS does not prove that every site's owner is honest: an encrypted connection can still lead to a fraudulent website.
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