Bandwidth*delay product (BDP) is a term primarily used in conjunction with the Transmission control protocol (TCP) to refer to the number of bytes necessary to fill a TCP "path". TCP has a concept of windows which are used for congestion control and for determining the optimum size of packet that is resilient to packet loss, packet truncation (due to link layer maximum transmission unit) or reordering. Generally, for TCP to obtain maximum speed, the formula is 3*BW*delay bytes, or three times the bandwidth times the delay of the end-to-end packet response.