In data communications, the bandwidth-delay product is the product of a data link's capacity (in bits per second) and its round-trip delay time (in seconds).[1] The result, an amount of data measured in bits (or bytes), is equivalent to the maximum amount of data on the network circuit at any given time, i.e., data that has been transmitted but not yet acknowledged. The bandwidth-delay product was originally proposed[2] as a rule of thumb for sizing router buffers in conjunction with congestion avoidance algorithm random early detection (RED).
A network with a large bandwidth-delay product is commonly known as a long fat network (LFN). As defined in RFC 1072, a network is considered an LFN if its bandwidth-delay product is significantly larger than 105 bits (12,500 bytes).