Bandwidth-delay product
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In data communications, bandwidth × delay product refers to the product of a data link's capacity (in bits per second) times its end-to-end delay (in seconds). The result, an amount of data measured in bits (or bytes), is equivalent to the amount of data "on the air" at any given time, i.e. the number of bytes that have been transmitted but not yet received.
Obviously, the bandwidth-delay product is higher for faster circuits and for long-delay links such as GEO satellite connections. The product is particularly important for protocols such as TCP that guarantee reliable delivery, as it describes the amount of yet-unacknowledged data that the sender has to duplicate in a buffer memory in case the client requires it to re-transmit a garbled or lost packet.
[edit] Examples
Customer on a DSL link, 1 Mbit/s, 200 ms one-way delay: 200 kbit = 25 kByte
High-speed terrestrial network: 100 Mbit/s, 100 ms: 10 Mbit = 1.25 MByte
Server on a saturated 1 Gbps link, average client delay 300 ms = 300 Mbit = 37.5 MByte total required for buffering
Speedguide.net provides a Bandwidth*Delay Calculator here: [1]
