Optimize network performance by calculating TCP throughput limits. Analyze bandwidth-delay product, window size efficiency, and packet loss impact using industry-standard formulas.
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TCP throughput determines how fast data can actually flow through your network connection. It's not just about bandwidth - factors like round-trip time (RTT), TCP window size, and packet loss significantly impact real-world performance. This calculator helps you understand and optimize your network's effective throughput.
TCP throughput is the effective data transfer rate achieved by the TCP protocol. While your link bandwidth defines the maximum possible speed, TCP's reliability mechanisms (acknowledgments, flow control, congestion control) often limit actual throughput. The Bandwidth-Delay Product (BDP) determines how much data can be 'in flight' at any time.
Bandwidth-Delay Product
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TCP throughput is limited by the Bandwidth-Delay Product (BDP). If your TCP window size is smaller than the BDP, you can't fully utilize your bandwidth. High RTT connections need larger windows. Additionally, packet loss dramatically reduces throughput due to TCP's congestion control algorithms.
BDP represents the amount of data that can be 'in flight' on a network path at any time. It's calculated as bandwidth × RTT. For example, a 100 Mbps link with 100ms RTT has a BDP of 1.25 MB. Your TCP window must be at least this size to fully utilize the link.
Packet loss has a severe impact on TCP throughput. The Mathis formula shows that throughput is inversely proportional to the square root of packet loss. Even 1% loss can reduce throughput by 90% on high-speed links. This is why lossy networks feel much slower than the bandwidth suggests.
Window Scaling (RFC 1323) allows TCP windows larger than 64KB. Without it, the maximum window is 65,535 bytes, limiting throughput on high-BDP links. Modern operating systems enable this by default. With scaling, windows up to 1GB are possible.
Use the ping command to your destination server: 'ping example.com'. The reported time is the RTT. For more accurate measurements, use multiple samples and take the average. Tools like mtr or pathping show RTT at each hop.
The optimal window size equals or exceeds your BDP. For a 100 Mbps link with 50ms RTT, you need at least 625 KB. For most modern internet connections, enabling TCP window scaling and letting the OS auto-tune is sufficient. Manual tuning may help for specialized applications.