TCP (Transmission Control Protocol)

TCP is a communication protocol to ensure reliable, ordered, and error-checked delivery of data between applications over a network; its like a courier service that ensures your package (data) reached its destination intact, in the right order, and without loss.

HOW IT WORKS ?

• Connection-Oriented Protocol:
  • TCP establishes a connection between two devices before transmitting data
  • This is like making a phone call where both parties say “hello” before talking to ensure they are connected
• Reliable Data delivery:
  • TCP ensures that all data is delivered correctly. If a packet is lost or corrupted, TCP retransmits it.
  • Its uses acknowledgments (ACKs) to confirm successful delivery.
• Ordered Delivery:
  • Packets may arrive at their destination in a jumbled order due to different routes taken across the network.
  • TCP reassembles the data in the correct order before passing it to the application
• Error Detection and Correction:
  • TCP includes error-checking mechanisms to detect corrupted packets and request retransmission.

TCP Process: Step-by-step:

• Connection establishment (The three-Way Handshake):

  • SYN (Synchronize):
    • The client sends a SYN packet to the server, indicating it wants to start a connection.
    • this packet also includes the client’s initial sequence number (ISN), used to keep track of data.
  • SYN-ACK (Synchronize + acknowledge):
    • The server responds with a SYN-ACK packet.
    • This acknowledges the client’s SYN and includes the server’s own sequence number.
  • ACK (Acknowledge):
    • The client sends an ACK back to the server, completing the handshake.
    • Now the connection is established, and data transfer can begin.

• Data Transmission:

  • once the connection is established, data is sent in packets.
  • Each packet includes:
    • Sequence numbers: indicate the position of the packet’s data within the overall message.
    • Acknowledgment numbers: confirm receipt of packets.

• Error Handling and Retransmission

  • If a packet is lost:
    • The receiver detects the missing sequence number.
    • It requests retransmission by sending a duplicate ACK.
  • If the sender doesn’t receive an acknowledgment in time, it retransmits the packet.

• Connection Termination:

  • To close a connection, TCP uses a four-step process:
    1. One side sends a FIN (finish) to indicate it wants to close the connection.
    2. The other side responds with an ACK to acknowledge the FIN.
    3. The second side then sends its own FIN to signal it’s ready to close.
    4. The first side sends an ACK, and the connection is terminated.

Visualizing TCP

Think of TCP as a polite, organized librarian:

1. It greets you (three-way handshake).
2. It carefully delivers books to you, ensuring none are missing or damaged (reliable delivery).