The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered, and error-checked delivery of a stream of octets (bytes) between applications running on hosts communicating via an IP network.
TCP is connection-oriented communication, and a connection between client and server is established before data can be sent.
Transmission Control Protocol * Data comes from the application layer and is packaged by TCP into segments which are then handed to the internet layer.
TCP Segment#
Protocol operation#
Connection establishment#
TCP 3-way handshake
Before transmission sending and receiving devices must acknowledge each other's presence and readiness to send and receive data.
- SYN: The active open is performed by the client sending a SYN to the server. The client sets the segment's sequence number to a random value A.
- SYN-ACK: In response, the server replies with SYN-ACK. The acknowledgement number is set to one more than the received sequence number i.e. A+1, and the sequence number that the server chooses for the packet is another random number, B.
- ACK: Finally, the client sends an ACK back to the server. The sequence number is set to the received acknowledgment value i.e. A+1, and the acknowledgment number is set to one more than the received sequence number i.e. B+1.
Note: Steps 1 & 2 establish and acknowledge the sequence number for one direction. Steps 2 & 3 establish and acknowledge the sequence number for the other direction. Following the completion of these steps, both the client and server have received acknowledgements anda full-duplex communication is established.
Connection termination#
Once transmission is complete - Sending device: FIN Receiving device: ACK, FIN Sending device: ACK