TCP

Problem

IP packets can: * disappear, * arrive twice, * arrive out of order. That's fine for some applications. But imagine downloading: BANK TRANSFER: €100 and pieces of the byte stream disappear.

Solution — TCP

TCP stands for Transmission Control Protocol. TCP creates a reliable ordered byte stream. It numbers data and uses acknowledgements and retransmissions so both sides can reconstruct the intended stream.

1 → 2 → X → 4
        ↓
    retransmit 3

Core idea: TCP turns unreliable packet delivery into a reliable ordered connection.