What are the five common requirements that network protocols must agree upon?

Message encoding, message formatting and encapsulation, message size, message timing, and message delivery options.

For two devices to understand each other, their protocols must pre-agree on five things — think of them as the layers of agreement needed before a single useful message can pass:

1. Message encoding - How information is converted into a transmittable form (a pattern of light, sound, or electrical signals) and decoded again at the other end.
2. Message formatting and encapsulation - The agreed structure and packaging of the data, including the header fields that say who it's from and to.
3. Message size - How large a single message may be, so the receiver can break large data into chunks the network and the destination can handle.
4. Message timing - When a device is allowed to send, how fast (flow control), and how long to wait for a reply (timeout).
5. Message delivery options - Whether the message goes to one device (unicast), a group (multicast), or all of them (broadcast).

Why it matters: miss agreement on any one of these and communication breaks — e.g. if the sender uses a 9000-byte message and the receiver only accepts 1500, the data is dropped even though everything else is correct.

Go deeper:

• Communication protocol — encoding, formatting, size, timing, and delivery treated as the elements protocols must agree on.