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Performance

TCP Throughput / BDP

Enter the bandwidth, the RTT and the TCP window size and compute the BDP, the real throughput limited by the window and the recommended window to fill the link. On high-latency links the window must be ≥ BDP to use the full bandwidth.

Mbps
ms
KB

Without scaling, the classic maximum is 64 KB. With window scaling (RFC 7323) it goes much higher.

%

If it is > 0, the Mathis limit (MSS=1460) is added as a reference.

Examples
redzilla.cl — tcp 
 
  
 
 
BDP (bandwidth × delay product)
 
—
 
—
 
 
 
Throughput with this window
 
—
 
—
 
 
 
Recommended window
 
—
 
to saturate the link
 
 
  
 
 BDP —  
 
 Throughput —  
 
 Optimal window —  
 
  
 
Diagnosis
 
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 How it is calculated · BDP, window and Mathis 
 
 1. BDP (bytes) = BW × RTT / 8,
            with BW in bps and RTT in seconds. It is the
            amount of data "in flight" needed to fill the link.

 
 2. Throughput limited by the window:
(window × 8) / RTT. A fixed window only lets you send
            those bytes per RTT.

 
 3. To saturate the link, the window must be
≥ BDP. On high-BDP links (lots of latency or
            bandwidth), 64 KB without scaling severely limits
            performance.

 
 4. With loss p > 0, the
            Mathis limit ≈ (MSS × 8) / (RTT × √p) bounds classic TCP
            throughput, independent of the window.

 
 
 
 
 
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