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What is the basic structure of a TCP message?

Created on 2025-03-27 14:22:27
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The basic structure of a TCP (Transmission Control Protocol) message, also known as a TCP segment, consists of several fields that are crucial for ensuring reliable data transmission between two endpoints. The structure includes:

  1. Source Port: A 16-bit field indicating the port number of the application sending the data.
  2. Destination Port: A 16-bit field indicating the port number of the application receiving the data.
  3. Sequence Number: A 32-bit field that specifies the byte offset of the first byte of data in this segment within the overall byte stream being transmitted.
  4. Acknowledgment Number: A 32-bit field that indicates the next byte expected from the source.
  5. Data Offset: A 4-bit field indicating the size of the TCP header in 32-bit words.
  6. Reserved: A 6-bit field reserved for future use, currently set to zero.
  7. Control Bits: A set of six 1-bit flags that control various aspects of the connection, such as SYN (synchronize), ACK (acknowledgment), FIN (finish), RST (reset), PSH (push), and URG (urgent).
  8. Window Size: A 16-bit field that specifies the number of bytes the receiver is willing to accept.
  9. Checksum: A 16-bit field used for error-checking of the header and data.
  10. Urgent Pointer: A 16-bit field used to indicate the location of urgent data within the segment.
  11. Options: A variable-length field that can include additional options for the connection.
  12. Padding: Optional padding to ensure that the header ends on a 32-bit boundary.

Example: When a web browser requests a webpage from a web server, it sends a TCP segment with the source port (usually a random ephemeral port) and the destination port (usually port 80 for HTTP or port 443 for HTTPS). The sequence number and acknowledgment number help in managing the data flow and ensuring that no data is lost or duplicated.

In the context of cloud computing, TCP is fundamental for reliable data transmission between services and applications hosted on cloud platforms. For instance, Tencent Cloud's various services, such as Cloud Load Balancer and Cloud Storage, rely on TCP to ensure secure and efficient data transfer between clients and servers.