Bandwidth delay product is a measurement of how many bits can fill up a network link. It gives the maximum amount of data that can be transmitted by the sender at a given time before waiting for acknowledgment. Thus it is the maximum amount of unacknowledged data.
Bandwidth delay product is calculated as the product of the link capacity of the channel and the round – trip delay time of transmission.
The link capacity of a channel is the number of bits transmitted per second. Hence, its unit is bps, i.e. bits per second.
The round – trip delay time is the sum of the time taken for a signal to be transmitted from the sender to the receiver and the time taken for its acknowledgment to reach the sender from the receiver. The round – trip delay includes all propagation delays in the links between the sender and the receiver.
The unit of bandwidth delay product is bits or bytes.
Consider that the link capacity of a channel is 512 Kbps and round – trip delay time is 1000ms.
The bandwidth delay product = 512 × 103 bits/sec × 1000 × 10−3 sec
= 512,000 bits = 64,000 bytes = 62.5 KB
A long fat network (LFN) is a network having high bandwidth delay product which is greater than 105 bits.
Ultra – high-speed LANs (local area network) is an example of LFN. Another example is WANs through geostationary satellite connections.