TCP prevents loss of data, duplication, and damage. It ensures that the sent message isn't out of order. These characteristics make it a reliable protocol, unlike UDP.
TCP synchronizes using a three-way handshake. Synchronization between two nodes begins when a TCP segment is sent with the SYN (0x02) flag set.
TCP sockets are one-to-one. A source node transmits messages to the destination node.
TCP sockets are one-to-one
A three-way handshake allows TCP to prevent out-of-order message delivery and duplicated transmission.
- Transmission begins when the
SYN(0x02)flag is set in a packet and is sent to the destination. - The destination receives the packet with the
SYN(0x02)flag and sends an acknowledgement to the source by setting theACK(0x10)flag in the reply. This stage is called SYN-ACK. - The source receives the SYN-ACK message and sends an
ACKsegment, which notes that each packet in the TCP messages contains a sequence number to maintain the order. - Once the transmission is done, the
FIN(0x01)flag is set in the next reply packet.
The three-way handshake protocol
The sequence numbers allow TCP to control the flow. TCP uses a sliding-window technique. If an ACK segment is not received in a particular period of time, then it retransmits the missing part of data. However, choosing an appropriate timeout is not an easy task. Therefore, in order to solve this issue, TCP uses adaptive retransmission.