These bits are not used. When URG bit is set to 1, It indicates the receiver that certain amount of data within the current segment is urgent.
Urgent data is pointed out by evaluating the urgent pointer field. The urgent data has be prioritized. Receiver forwards urgent data to the receiving application on a separate channel.
Request segment is sent for connection establishment during Three Way Handshake. When PSH bit is set to 1, All the segments in the buffer are immediately pushed to the receiving application.
No wait is done for filling the entire buffer. This makes the entire buffer to free up immediately. It just causes all the segments in the buffer to be pushed immediately to the receiving application. The same order is maintained in which the segments arrived.
When RST bit is set to 1, It indicates the receiver to terminate the connection immediately. It causes both the sides to release the connection and all its resources abnormally. The transfer of data ceases in both the directions. It may result in the loss of data that is in transit. This is used only when- There are unrecoverable errors. There is no chance of terminating the TCP connection normally. When SYN bit is set to 1, It indicates the receiver that the sequence number contained in the TCP header is the initial sequence number.
Request segment sent for connection establishment during Three way handshake contains SYN bit set to 1. When FIN bit is set to 1, It indicates the receiver that the sender wants to terminate the connection. Window Size- Window size is a 16 bit field. It contains the size of the receiving window of the sender. It advertises how much data in bytes the sender can receive without acknowledgement. Thus, window size is used for Flow Control. It usually increases during TCP transmission up to a point where congestion is detected.
After congestion is detected, the window size is reduced to avoid having to drop packets. Checksum- Checksum is a 16 bit field used for error control. It verifies the integrity of data in the TCP payload. Sender adds CRC checksum to the checksum field before sending the data. Receiver rejects the data that fails the CRC check. The Source port is optional. In this case, the port number will be an ephemeral port number.
Generally, the value is from to is used for a temporary port number. Port number of the destination user of receiving TCP. It is set in the TCP header by the user. The parameter is mandatory. Over the public internet, the port numbers are also called well-known ports. For example, a website runs over always a default port Technically it can use any other port also e.
In that case, a TCP client who is using a web browser should also know the port number along with the website domain name URL, www. A bit integer value, preset from 5 to 7 bytes in TCP header. TCP does the sequence control using the sequence number. When the sender sends the messages to the receiver, TCP uses the IP network to reach the destination.
There might be multiple paths to reach from source to destination. This may lead to the situation where the message sent earlier reaches the destination later. On the receiver, MSG2 reaches first. This creates a sequencing issue. TCP is a reliable protocol. What does this mean?
This means that TCP makes sure that a message sent to the remote layer has been received. It does this by using the TCP ack number. This is a 32 bits numeric value in the TCP header. Ack number is set by the receiver. The value signifies the expecting next sequence number segment from the sender. The next example is the detailed explanation of the TCP Ack number usage in the protocol. It sends M1 and M2 then waits for the ack from the remote, before sending M3. Now the sender will send the M3.
Here you might be thinking about how TCP decides how many segments it should be sent at a single time. We will cover this incoming section for Windows. In the beginning, we have mentioned that receiving TCP, uses the header to read the application data. A TCP message is a stream of bytes with a header and data.
To read user bytes, the TCP layer should know how many bytes are present for the header before user data. This is determined by the 4 bits value in the header. It is variable in nature and always multiple of 32 bits. The variable is in nature because there are optional parameters. Generally, the TCP header size is 20 bytes.
TCP Header specifies various fields required during transmission. TCP Header size ranges from 20 bytes to 60 bytes. Akshay Singhal. Publisher Name. Port numbers indicate which end to end sockets are communicating. The length of TCP header always lies in the range- [20 bytes , 60 bytes]. The range of header length field value is always [5, 15].
0コメント