Transmission Control Protocol - TCP

Last Updated : 13 Oct, 2025

Transmission Control Protocol (TCP) is a connection-oriented protocol for communications that helps in the exchange of messages between different devices over a network. It is one of the main protocols of the TCP/IP suite. In OSI model, it operates at the transport layer(Layer 4). It lies between the Application and Network Layers which are used in providing reliable delivery services. The Internet Protocol (IP), which establishes the technique for sending data packets between computers, works with TCP.

TCP establishes a reliable connection between sender and receiver using the three-way handshake (SYN, SYN-ACK, ACK) and it uses a four-step handshake (FIN, ACK, FIN, ACK) to close connections properly.
It ensures error-free, in-order delivery of data packets.
It uses acknowledgments (ACKs) to confirm receipt.
It prevents data overflow by adjusting the data transmission rate according to the receiver’s buffer size.
It prevents network congestion using algorithms like Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery.
TCP header uses checksum to detect corrupted data and requests retransmission if needed.
It is used in applications requiring reliable and ordered data transfer, such as web browsing, email, and remote login.

Features of TCP

Some of the most prominent features of Transmission control protocol are mentioned below.

Segment Numbering: Each byte of data is numbered, and segments carry sequence numbers. Acknowledgment numbers confirm successful receipt.
Connection-Oriented: Sender and receiver remain connected until data transfer is complete. Data order is preserved.
Full Duplex: Data can flow in both directions simultaneously, improving efficiency.
Flow Control: Uses a sliding window to prevent the sender from overwhelming the receiver.
Error Control: Detects and manages corrupted, lost, duplicate, or out-of-order segments to ensure reliability.
Congestion Control: Adjusts the sending rate based on network congestion to avoid overload.

Internet Protocol (IP)

Internet Protocol (IP) is a method that is useful for sending data from one device to another from all over the internet. It is a set of rules governing how data is sent and received over the internet. It is responsible for addressing and routing packets of data so they can travel from the sender to the correct destination across multiple networks. Every device contains a unique IP Address that helps it communicate and exchange data across other devices present on the internet.

Working of Transmission Control Protocol (TCP)

TCP manages data transmission between two devices by dividing messages into smaller units called segments and ensuring they are delivered reliably and in order.

Data Segmentation: The application data is divided into small segments for efficient transmission instead of sending it all at once.
Routing: Each segment can take a different route through the network, depending on traffic or congestion, but all segments eventually reach the same destination.
Reassembly: At the receiver’s end, TCP reassembles these segments into the original message using sequence numbers.
Acknowledgment: The receiver sends ACK (acknowledgment) messages back to confirm successful receipt of each segment.
If an acknowledgment isn’t received, TCP retransmits the missing segment.
Error and Flow Control: TCP uses checksums to detect errors and a sliding window mechanism to control the flow of data, ensuring the receiver isn’t overwhelmed.

Example: When a user requests a webpage:

The browser (client) uses HTTP, which relies on TCP to create a connection.
TCP breaks the web page (HTML file) into packets and hands them to the IP layer for delivery.
At the user’s end, TCP reassembles the packets and confirms successful transmission through acknowledgments.

Advantages of TCP

It is a reliable protocol which provides an error-checking mechanism as well as one for recovery.
It makes sure that the data reaches the proper destination in the exact order that it was sent.
It is a well-documented and widely implemented protocol, maintained by standards organizations like the IETF (Internet Engineering Task Force).
It works in conjunction with IP (Internet Protocol) to establish connections between devices on a network.

Disadvantages of TCP

TCP is made for Wide Area Networks, thus its size can become an issue for small networks with low resources.
TCP runs several layers so it can slow down the speed of the network.
It is not generic in nature. It cannot represent any protocol stack other than the TCP/IP suite. E.g., it cannot work with a Bluetooth connection.
No modifications since their development around 30 years ago.