1.1.e Explain TCP operations - 1.1.e (iv) Windowing

1.1.e (iv) Windowing

The window size is the amount a unacknowledged data that can be in transit at a given time. This is negotiated between two hosts. While connectivity is reliable, all packets are being received, and upper level protocols are accepting the packets and keeping the buffers empty, hosts will attempt to increase the window size. In the event of missing packets, filling buffers, etc, the hosts will reduce the segment size.

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.

http://packetlife.net/blog/2010/aug/4/tcp-windows-and-window-scaling/