TCPsegmentit

TCPsegmentit, or TCP segments, are the basic units of data carried by the Transmission Control Protocol (TCP). In network communication, TCP segments carry application data across an IP network with reliability and ordered delivery.

Composition and structure: Each TCP segment consists of a header and a payload. The header contains fields such as source and destination ports, sequence number, acknowledgment number, data offset, flags (including SYN, ACK, FIN, RST, PSH, URG), window size, checksum, urgent pointer, and optional parameters. The payload holds a portion of the application data being transmitted.

Function and behavior: TCP segments enable reliable, connection-oriented transport. The sender assigns sequence numbers to bytes; the receiver uses acknowledgments to confirm receipt and triggers retransmission on timeout or duplicate ACKs. Flow control is achieved via the receiver window size, while congestion control employs algorithms like slow start and congestion avoidance to adapt to network conditions.

Maximum Segment Size: The MSS is negotiated during the TCP three-way handshake and is typically limited by the IP MTU minus the combined TCP/IP headers, helping to minimize fragmentation.

Lifecycle and processing: Data is handed to TCP by the application, segmented for transmission, and transmitted to the peer. The receiver reassembles the data stream from segments in order and delivers it to the application. The urgent pointer provides a mechanism for out-of-band data, though it is rarely used in modern practice. The checksum protects data integrity.

Relation to other protocols: Compared with UDP, TCP provides reliability and ordering at the cost of additional overhead. TCP segments are used by many application-layer protocols, including HTTP(S), SMTP, and FTP.

Historical context: TCP was defined in RFC 793 (1981) and has evolved through subsequent RFCs addressing congestion control, reliability improvements, and performance enhancements. If the term TCPsegmentit is used, it may reflect Finnish terminology for multiple TCP segments.