TCP Data Header Format description

The concept of TCP has been mentioned many times. Today we will introduce the TCP packet header format for this Protocol. In this article, we will give a detailed description of its organization and basic meaning, as well as the role of each part.

TCP Data Header

The figure shows the format of the TCP Data header.

Source Port and destination port: 16-bit long. Identifies the remote and local port numbers.

Sequence Number: 32-bit long. Indicates the order of sent data packets.

Confirmation No.: 32-bit long. The serial number of the next datagram you want to receive.

TCP Data header DE Header Length: 4-bit length. Indicates the number of 32 characters in the TCP header.

The next six digits are not used.

ACK: ACK position 1 indicates that the confirmation number is valid. If ACK is 0, the datagram does not contain confirmation information, and the validation field is omitted.

PSH: Indicates data with the PUSH flag. Therefore, the receiver can send the request datagram to the application as soon as it arrives, instead of waiting until the buffer is full.

RST: Used to reset connections that encounter errors due to host crashes or other causes. It can also be used to reject illegal data packets or connection requests.

SYN: used to establish a connection.

FIN: Used to release connections.

Window Size: 16-bit long. The window size field indicates the number of bytes that can be sent after the bytes are confirmed.

Checksum: 16-bit long. It is set to ensure high reliability. It verifies the sum of the header, data, and pseudo TCP header.

Optional: 0 or multiple 32-bit characters. The options include maximum TCP load, window ratio, and resend datagram.

Maximum TCP load: each host is allowed to set the maximum TCP load capacity it can accept. During the connection establishment, both parties declare their maximum load capacity, and select smaller ones as the standard. If this option is not used by a host, the default load capacity is 536 bytes.

Window proportion: allows the sender and receiver to agree on an appropriate window proportion factor. This factor allows the sliding window to reach a maximum of 232 bytes.

Select resend datagram for the TCP protocol data header: This option allows the recipient to request to send one or more specified datagram.