TCP segment

RU: TCP-сегмент

The Protocol Data Unit (PDU) of TCP: a header plus a payload of application bytes. The 20-byte minimum header carries source and destination ports, a 32-bit sequence number, a 32-bit acknowledgment number, control flags (SYN, ACK, FIN, RST), a receive-window size, and a checksum. Everything TCP guarantees — ordering, reliability, flow control — is implemented through these header fields.