Tools

Transmission Control Protocol

Introduction

  • TCP (Transmission Control Protocol) is a connection-oriented protocol, meaning that a connection must be established before data transmission.
  • It ensures reliable, ordered, and error-checked delivery of data between applications.
  • TCP operates in full-duplex mode and supports point-to-point communication.

TCP Connection Establishment

3-Way Handshake

Before data transmission begins, TCP establishes a connection using a three-step process:

  1. SYN (Synchronize) → The client sends a SYN segment to the server, requesting a connection.
  2. SYN-ACK (Acknowledge) → The server responds with a SYN-ACK, acknowledging the request.
  3. ACK (Acknowledge) → The client sends an ACK, confirming the connection is established.

After this handshake, data transmission begins.

Stop-and-Wait vs. Pipelined Protocols

Stop-and-Wait Protocol

  • The sender transmits one packet at a time and waits for an acknowledgment (ACK) before sending the next packet.
  • Simple but inefficient, especially for long-distance communication.

Pipelined Protocols (Efficient Data Transmission)

  • The sender transmits multiple packets before waiting for an acknowledgment.
    The Go-Back-N (GBN) Protocol
    • The sender can have up to N unacknowledged packets in the pipeline.
    • If a packet is lost, all subsequent packets must be retransmitted.

TCP Congestion Control

Slow-Start Phase

  • Initially, TCP doubles the congestion window size with each round-trip time (RTT), allowing a quick increase in transmission speed.

Additive Increase and Multiplicative Decrease (AIMD)

  • Additive Increase: If there is no congestion, TCP gradually increases its congestion window.
  • Multiplicative Decrease: When packet loss occurs, TCP reduces the congestion window exponentially, preventing further congestion.

TCP Connection Termination (Closure)

TCP uses a 4-way handshake to close a connection:

  1. FIN → The sender sends a FIN packet, requesting to close the connection.
  2. ACK → The receiver acknowledges the request.
  3. FIN → The receiver sends its FIN packet when ready to close.
  4. ACK → The sender acknowledges the receiver’s FIN, completing the termination.

After termination, TCP enters the TIME-WAIT state before completely closing the connection.

Reference Books

  1. Kurose, J. F., & Ross, K. W. Computer Networking: A Top-Down Approach. Pearson.
  2. Tanenbaum, A. S., & Wetherall, D. J. Computer Networks. Pearson.