ITPEC IP October 2021 Question 33

Devices from different manufacturers or with different OS can communicate if they use the same protocol — a protocol is the shared set of rules for communication.

A communications protocol fixes the data format, the order of the exchange (who sends what, and when) and what to do when something goes wrong. TCP/IP and HTTP are examples. As long as both ends follow the same rules, their hardware and OS do not matter: a Windows PC and a smartphone reach the same web server through HTTP over TCP/IP.

Answer (d)

Why not others:

• •(a) — analog communication has protocols too; a fax machine, for example, follows a set procedure when it exchanges pages over an analog telephone line
• •(b) — protocols can be made by manufacturers (proprietary protocols such as IBM's SNA or Apple's AppleTalk) as well as by standards bodies such as ISO, ITU-T and IETF
• •(c) — protocols also define abnormal cases: error detection, retransmission and timeouts

Key rule: Interoperability comes from shared protocols, not from identical hardware or software; that is why open standard protocols such as TCP/IP let any vendor's device join the Internet.

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