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The TCP Upstream Rate and TCP Downstream Rate visualizations show TCP throughput rates measured in Mbps (megabits per second.) Throughput (also often referred to as “goodput”) is the amount of application-layer data delivered from the client to the server (upstream) or from the server to the client (downstream) per second. The protocol overhead is not included, so when we talk, for example, about the TCP throughput rate of 1 Mbps, we mean that 125 Kbytes of actual data payload were sent between two network nodes during one second, not including TCP, IP, and Ethernet or 802.11 headers.
Throughput rates are one of the most important real-world metrics of a WLAN, because they determine the end user experience and network-related application performance.
Double-clicking on the TCP Upstream and Downstream Rate legend on the status bar allows you to configure the color scheme and change its value range.
Suggested Solutions
When low throughput areas are discovered, the following solutions are suggested:
| § | Verify that the actual PHY rate is sufficient. Throughput rates cannot exceed PHY rates; in practice, they are about 50% lower than PHY rates. For example, if the PHY rate in the given area is only 2 Mbps, you should not expect the throughput rate to exceed 1 Mbps. In practice, it might be as low as 0.1 or 0.2 Mbps, depending on other conditions. |
| § | Other common reasons for low throughput rates are interference and excessive network traffic. The Signal-to-Interference Ratio visualization available for passive surveys might provide insight into interference issues. Excessive network traffic might be caused either by oversubscription (too many clients per AP) or by excessive network load by some clients. The former can be addressed by increasing the number of APs, while the latter should be verified and handled by network traffic monitoring software. |
| § | The client-AP part of the link might not be the bottleneck. Even if the wireless link quality is excellent and provides high throughput rates, the wired side of the network might be the problem. For example, if the throughput test server utility is running on a computer equipped with a 100 Mbps adapter, your throughput rates in this test will never exceed 80 or 90 Mbps, despite the fact that the wireless side of the link might provide 150 or 200 Mbps throughput. Make sure that the bandwidth of the wired side exceeds the bandwidth of the wireless side; check Ethernet adapter speeds, switch port speeds, cabling, etc. All the hardware between the client and server should support the speed of at least 1 Gbps. |
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