1.1.e Explain TCP operations

1.1.e [iv] Windowing

Flow control allows us to deal with a situation when a sending computer tries to transmit information at a faster rate than the destination computer can receive and process it. This can happen if the receiving computers have a heavy traffic load in comparison to the sending computer, or if the receiving computer has less processing power than the sending computer.

Sliding-window flow control is best utilized when the buffer size is limited and pre-established. During a typical communication between a sender and a receiver the receiver allocates buffer space for n frames ( n is the buffer size in frames). The sender can send and the receiver can accept n frames without having to wait for an acknowledgement. The receiver acknowledges a frame by sending an acknowledgement that includes the sequence number of the next frame expected. This acknowledgement announces that the receiver is ready to receive n frames , beginning with the number specified. Both the sender and receiver maintain what is called a window. The size of the window is less than or equal to the buffer size.

Sliding window flow control has a far better performance than stop-and-wait flow control. For example in a wireless environment data rates are low and noise level is very high, so waiting for an acknowledgement for every packet that is transferred is not very feasible. Therefore , transferring data as a bulk would yield a better performance in terms of higher throughput.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1132-1137).  . Kindle Edition.