TCP Flow Control Mechanism

Flow control is that balances the sender’s rate of sending data with the receiver’s rate of properly receiving data. Why do we need TCP flow control? Flow control is required because the sender may wish to send data faster than the receiver can process it. This can happen if the receiving application is processing data slower than the sending application is generating it. Sender can not overrun receiver with lots of information. Allow receiver to restrict transmission until it has sufficient buffer space to accommodate more data. Flow control in TCP is similar to Data Link layer’s Go Back N(TCP Tahoe, Reno, new Reno) and Selective Repeat(TCP Sack). However, there are differences as well in flow control mechanism of TCP and Data Link layer. TCP Flow control is Byte oriented and TCP sliding window is of variable size, but Data Link Flow control is use Frames and fixed size window. TCP uses sliding window to handle flow control.

When an acknowledgment for packet 1 is received the window slides to the right and allows the transmission of packet 9. In TCP, there is a window size, so if you tell receiver by the window size value, the receiving side can send the data without an ACK.