Computer Science A2 · Communication and internet technologies. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A protocol is an agreed set of rules for communication. Two computers can exchange data only if both use the same rules for format, timing, addressing and error checking. This is why machines from different makers, with different operating systems, can talk to each other.
Protocols are organised as a stack of layers. Each layer has its own job and passes data only to the layer above or below, so one layer can be changed without changing the others.
The TCP/IP suite has four layers: Application, Transport, Internet, Link. The sender's data goes down the stack, each layer adding a header. At the receiver it goes up, and each layer removes its header.
Students swap the Transport and Internet layers. Remember that port numbers and segments belong to the Transport layer, and IP addresses, packets and routing belong to the Internet layer below it.
Answer: IMAP.
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