networks//network protocols//TCP/IP

The Internet stack: **IP** provides addressing and routing, **TCP** and **UDP** are transport protocols on top of it (TCP ordered and reliable with connections, UDP a bare datagram). Together they move bytes between addressed hosts; they say nothing about what the bytes mean.

The Internet stack: IP provides addressing and routing, TCP and UDP are transport protocols on top of it (TCP ordered and reliable with connections, UDP a bare datagram). Together they move bytes between addressed hosts; they say nothing about what the bytes mean.

That last point is the one automation people insist on: TCP/IP transports data but does not define what each industrial value is. The meaning is the application protocol above, Modbus TCP, OPC UA, MQTT or HTTPS (protocol stack).

Moving a serial protocol onto TCP/IP changes the transport, not the vocabulary: Modbus TCP keeps Modbus's registers and swaps a serial address for an IP address.

TCP's reliability comes from retransmission and waiting, which is exactly what a hard real-time loop cannot afford; industrial Ethernet variants that need bounded timing bypass or constrain the TCP/IP path (determinism).