Source (sender), destination (receiver), and a channel (the media that carries the message between them).

Every communication requires three elements:

1. Source (Sender) - The device or person originating the message
2. Destination (Receiver) - The device or person receiving the message
3. Channel (Media) - The pathway that provides the route for communications to occur

Key point: Networks can vary in size and complexity, but it is not enough to have a connection - devices must agree on "how" to communicate.

Go deeper:

• Telecommunications — basic system (transmitter, channel, receiver) — the same source/channel/destination model underlies every communication system.
• Communication protocol — how the three elements are governed by agreed rules.

A protocol is the set of rules a communication follows; without shared rules, sender and receiver cannot reliably understand each other.

A protocol is a set of rules that communications will follow.

Why protocols are necessary:

• All communications are governed by protocols
• Protocols define the rules that communications follow
• These rules vary depending on the specific protocol being used

Just like humans need agreed-upon rules to communicate effectively (language, grammar, turn-taking), network devices need protocols to exchange data successfully.

Go deeper:

• Communication protocol — full overview of what protocols define and why layering matters.
• RFC 1122 — Requirements for Internet Hosts — a primary-source example of how protocol rules are precisely specified.