Protocols — common mistakes

When asked to explain the need for protocols, don't just list protocol names like HTTP or FTP. Instead, explain the functions they provide, such as ensuring data integrity, managing flow control, and enabling devices from different vendors to communicate. Use terms like 'interoperability' and 'standardisation'.

Different communication tasks have different requirements. For example, transferring a large file (using FTP) requires high reliability and error checking, but speed might be secondary. In contrast, streaming a live video (often using UDP) prioritises speed and continuous flow over perfect accuracy; a few lost pixels are acceptable, but a long pause for retransmission is not. The TCP/IP model uses a 'stack' of protocols, each specialised for a different layer of the communication process, from physical transmission to application-level data.

Yes, HTTP (Hypertext Transfer Protocol) is an application-layer protocol. It defines the rules for how web browsers and web servers request and send web page data (like HTML files, images, and scripts). It sits 'on top' of other protocols like TCP/IP, which handle the reliable transport of the HTTP messages across the internet.

If the handshaking process fails at any step, a stable connection is not established. For example, if the client sends a SYN packet but receives no SYN-ACK from the server, it will assume the server is offline, unavailable, or has rejected the connection. The client's operating system will eventually report a 'connection timeout' error to the application, and no data transfer will occur.