TCP – Transmission Control Protocol

Transmission Control Protocol (TCP) is one of the core protocols of the Internet Protocol (IP) suite, which is crucial for enabling reliable communication over networks. It is designed to provide a reliable, ordered, and error-checked delivery of a stream of bytes between applications running on hosts communicating via an IP network. TCP is widely used for various applications such as web browsing, email, file transfers, and many other network services that require data integrity and accurate delivery.

Distinguishing Features of TCP

Transmission Control Protocol (TCP) is characterized by several key features that distinguish it from other network protocols. These features ensure reliable, ordered, and error-checked delivery of data across networks, making TCP suitable for a wide range of applications. Here are the primary distinguishing features of TCP:

  1. Connection-Oriented Communication
    • Three-Way Handshake: TCP establishes a connection between the sender and receiver using a three-way handshake before data transfer begins. This process ensures that both ends are ready and agree to establish a communication session.
    • Connection Maintenance: Once established, the connection remains active until the data transfer is complete. The connection is then gracefully terminated using a four-way handshake.
  2. Reliable Data Transfer
    • Acknowledgments (ACKs): TCP ensures reliable data delivery by requiring the receiver to send back an acknowledgment for each packet received. If the sender does not receive an ACK within a certain timeframe, it retransmits the packet.
    • Retransmissions: Lost or corrupted packets are retransmitted until they are correctly received and acknowledged.
  3. Ordered Data Transfer
    • Sequence Numbers: Each byte of data is assigned a sequence number, which allows the receiver to reassemble the data in the correct order, even if packets arrive out of sequence.
    • Reordering: The receiver uses sequence numbers to reorder packets into the original data stream before passing them to the application layer.
  4. Error Detection and Correction
    • Checksums: Each TCP segment includes a checksum that the receiver uses to verify the integrity of the data. If the checksum does not match, the segment is considered corrupted and is discarded.
    • Error Handling: Corrupted segments are detected and retransmitted to ensure data integrity.
  5. Flow Control
    • Sliding Window Protocol: TCP uses a sliding window protocol for flow control, which allows the sender to send multiple packets before needing an acknowledgment for the first one, but within the limits set by the receiver’s buffer capacity.
    • Window Size Adjustment: The receiver advertises a window size that indicates how much data it can accept at a time. The sender adjusts its transmission rate based on this window size to avoid overwhelming the receiver.
  6. Congestion Control
    • Congestion Avoidance Algorithms: TCP implements algorithms such as Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery to prevent and manage network congestion.
    • Dynamic Adjustment: The sender adjusts its transmission rate based on network conditions, such as packet loss or delay, to maintain optimal throughput without causing congestion.
  7. Full Duplex Communication
    • Bidirectional Data Flow: TCP supports full duplex communication, meaning data can be sent and received simultaneously between two endpoints. This is essential for interactive applications like web browsing and online gaming.
  8. Stream-Oriented Protocol
    • Continuous Data Stream: TCP treats data as a continuous stream of bytes, rather than discrete packets. This allows for more flexible and efficient data handling by the applications.
  9. Multiplexing
    • Port Numbers: TCP uses port numbers to distinguish between different applications on the same host. This allows multiple network services to run simultaneously on a single device.
  10. Scalability and Efficiency
    • Adaptive Retransmission: TCP adjusts its retransmission timeout dynamically based on round-trip time (RTT) measurements, improving performance and efficiency.
    • Selective Acknowledgments (SACK): An optional feature that allows the receiver to inform the sender about all segments that have been received successfully, thus allowing the sender to retransmit only the missing segments.

How TCP Works

1. Connection Establishment (Three-Way Handshake): TCP uses a three-way handshake process to establish a connection between the client and server:

  • SYN: The client sends a SYN (synchronize) packet to the server to initiate the connection.
  • SYN-ACK: The server responds with a SYN-ACK (synchronize-acknowledge) packet to acknowledge the client’s request.
  • ACK: The client sends an ACK (acknowledge) packet back to the server, completing the handshake and establishing the connection.

2. Data Transmission : Once the connection is established, data transmission can begin:

  • Segmentation: The sender divides the data into segments, each with a sequence number.
  • Transmission: Segments are transmitted to the receiver, which acknowledges each segment received.
  • Reassembly: The receiver reassembles the segments into the original data stream based on the sequence numbers.

3. Connection Termination : After the data transfer is complete, the connection is terminated using a four-way handshake process:

  • FIN: The sender sends a FIN (finish) packet to indicate the end of data transmission.
  • ACK: The receiver acknowledges the FIN packet with an ACK.
  • FIN: The receiver sends its own FIN packet to indicate that it has no more data to send.
  • ACK: The sender acknowledges the receiver’s FIN packet, completing the termination process.
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