TCP (Transmission Control Protocol) is one of the main transport layer protocols used in the Internet Protocol suite, commonly referred to as the TCP/IP suite. Its primary responsibility is to provide reliable, ordered, and error-checked delivery of data between applications running on hosts in a network. Here’s an overview:

Reliability:

  • TCP ensures data is delivered reliably by retransmitting any data that is not acknowledged by the receiver.
  • It uses acknowledgments (ACKs) to confirm the receipt of data segments.
  • It also handles out-of-order data and ensures data is delivered to the application layer in the correct sequence.

Flow Control:

  • TCP uses a mechanism called sliding window flow control to ensure that a sender does not overwhelm a receiver by sending too much data at once.

Error Checking:

  • Every TCP segment contains a checksum to verify the integrity of the data. If the checksum doesn’t match at the receiver’s end, the segment is discarded.

Connection-oriented:

  • Before data transmission begins, TCP establishes a connection using a three-way handshake. This sets up the initial sequence numbers and acknowledges that both sides are ready to transmit.
  • The three steps of the handshake are: SYN, SYN-ACK, and ACK.

Port Numbers:

  • TCP uses port numbers to identify specific processes/applications on both the sender and receiver devices. This allows multiple processes on a single device to communicate over TCP simultaneously.

Segmentation:

  • Large messages or chunks of data are divided into smaller segments before being sent over the network. The receiver then reassembles these segments.

Congestion Control:

  • TCP has built-in mechanisms to detect and handle network congestion. It adjusts the rate of data transmission based on network conditions.

Termination:

  • Connections are terminated through a four-step process involving FIN and ACK messages.

Enhancements and Variants:

  • Over the years, several variants and enhancements of TCP have been developed to address specific challenges. Examples include TCP Tahoe, Reno, NewReno, and CUBIC, each introducing different congestion control strategies.

TCP is widely used for many internet applications like web browsing, email, and file transfer because of its reliability. However, this reliability comes at the cost of additional overhead and latency, making it less suitable for real-time applications like voice or video streaming, where UDP (User Datagram Protocol) might be preferred.