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Bandwidth-Delay Product
The data "in flight" on a link at any moment. For TCP to keep a high-bandwidth, high-latency link saturated, the receive window must be at least the BDP. Long Fat Networks (LFNs) need RFC 1323 window scaling.
Common: LAN 1–5 ms · US coast-to-coast ~70 ms · transcontinental 100–250 ms · satellite 600+ ms
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Frequently Asked Questions
What is the bandwidth-delay product?
BDP is bandwidth multiplied by round-trip time — the amount of data "in flight" needed to keep a link fully used. If your TCP window is smaller than the BDP, you cannot fill the pipe.
Why does high latency reduce my throughput?
On a high-BDP path (fast link, long RTT), a small TCP receive window caps throughput regardless of bandwidth, because the sender must pause for ACKs before a full window of data is acknowledged.
When is TCP window scaling (RFC 1323) needed?
Whenever the BDP exceeds 64 KB, the classic 16-bit window limit. Window scaling extends the window so long-fat networks (satellite, transcontinental) can reach full speed.
