Transport Layer TCP transmission control protocol

TCP: Transmission Control Protocol)

The transport control protocol is a transport layer protocol that enables reliable data transmission in TCP/IP groups, and implements virtual connection services for applications through sequential response, forward packets when necessary. In combination with the IP protocol, TCP represents the core of the network protocol.

Most network applications run on the same machine, and the computer must be able to ensure that the correct software application at the destination obtains data packets from the source address, and the reply of the correct application on the source computer to obtain the selection path. This process is completed by using the TCP "port number. The connection between the network IP address and the port number must have a unique identifier, which is called "socket" or "endpoint ". For reliable communication, TCP establishes a connection or virtual circuit between the endpoints.

The TCP Service provides data stream transmission, reliable lines, effective traffic control, full duplex operations, and Multiplexing technologies.

For data stream transmission, TCP sends a non-structured byte stream defined by the serial number. This is advantageous to the application because the application does not need to be divided into blocks before being sent out of TCP. TCP can combine bytes into fields and then send them to IP addresses.

TCP is a connection-oriented end-to-end reliable protocol and ensures the order of transmitted data packets. The order is ensured by a response serial number, which tells the receiver the sender of the desired next packet. If you do not receive a response to this package within the specified time, You Need To resend the package. TCP's reliable mechanism allows devices to process lost, deleted, and read error packets. The suspension mechanism allows devices to monitor lost packets and request resends.

TCP provides effective traffic control. When a confirmation response is returned to the sender, the receiving TCP process will imply the highest serial number, which can receive and ensure that no overflow occurs.

Full-duplex operation: the TCP process can send and receive packets simultaneously.

Multiplexing in TCP: a large number of upper-layer concurrent sessions are multiplexing During Single connection.

Protocol Structure

Source Port-identifies the point where the upper-layer Source processor receives the TCP Service.
Destination Port-identifies the point at which the upper-layer target processor receives the TCP Service ..
Sequence Number-the Sequence Number of the first byte of the Data allocated to the current information. In the connection establishment phase, this field is used to set the initial serial number in the transmission.
Acknowledgment Number-the serial Number of the next byte of data that the data packet sender expects to receive. This value is always sent once the connection is successful.
Data Offset-4 bits. The 32-bit serial number in the TCP header indicates the start position of the data.
Reserved-6 bits. Reserved for backup. It must be set to 0.
Control Bits Flags)-6 Bits. Transmit various control information. The control bit can be:
Window-16 bits. Specify the size of the Receiving Window of the sender, that is, the size of the Eight-bit cache zone available for data.
Checksum-16 bits. Indicates whether the protocol header is damaged during transmission.
Urgent Pointer-16 bits. Point to the first important Data byte in the data packet.
Option + Padding-specify various TCP options. There are two possible options: an eight-bit (Optional) Type and an eight-bit (Optional) Type, an eight-bit (optional) length, and an actual eight-Bit Data Group.
Data-contains upper-layer information.

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