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4. Glossary

This section contains definitions of terms used in this document.

ACK (Acknowledgment): A control bit in the TCP header used to acknowledge successful receipt of data. Also refers to a segment with the ACK bit set.

Acknowledgment Number: A 32-bit field in the TCP header containing the next sequence number the sender expects to receive.

Connection: A logical communication path established between two TCP endpoints, uniquely identified by source address, source port, destination address, and destination port.

Datagram: A unit of data transmitted at the network layer, containing an IP header and payload (such as a TCP segment).

FIN (Finish): A control bit in the TCP header used to indicate that the sender has finished sending data and requests connection closure.

ISN (Initial Sequence Number): The starting sequence number chosen when establishing a connection.

MSS (Maximum Segment Size): The maximum data segment size that a TCP endpoint is willing to receive.

Port Number: A 16-bit number used to identify a specific application or service on a host.

RST (Reset): A control bit in the TCP header used to abnormally terminate a connection.

RTT (Round-Trip Time): The time required for a packet to travel from sender to receiver and back with acknowledgment.

Segment: The basic unit of data transmission in TCP, including the TCP header and optional application data.

Sequence Number: A 32-bit field in the TCP header that identifies the position of the first data byte in the segment.

SYN (Synchronize): A control bit in the TCP header used to synchronize sequence numbers during connection establishment.

TCB (Transmission Control Block): A data structure containing TCP connection state information.

Three-Way Handshake: The process of establishing a TCP connection, involving the exchange of SYN, SYN-ACK, and ACK segments.

Window: The amount of data the receiver is willing to accept, used for flow control.

Window Scale: A TCP option that allows window sizes to exceed 65,535 bytes.

State Terms:

  • CLOSED: Represents no connection state at all
  • LISTEN: Waiting for a connection request from any remote TCP
  • SYN-SENT: Waiting for a matching connection request after sending a connection request
  • SYN-RECEIVED: Waiting for confirmation after receiving and sending a connection request
  • ESTABLISHED: Connection is established, data transfer can occur
  • FIN-WAIT-1: Waiting for a connection termination request from remote TCP or acknowledgment of previously sent termination request
  • FIN-WAIT-2: Waiting for a connection termination request from remote TCP
  • CLOSE-WAIT: Waiting for a connection termination request from local user
  • CLOSING: Waiting for acknowledgment of connection termination request from remote TCP
  • LAST-ACK: Waiting for acknowledgment of previously sent connection termination request
  • TIME-WAIT: Waiting for enough time to ensure remote TCP received acknowledgment of its termination request
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