Detecting Wireless LAN Bottlenecks Using TCP Connection Measurement at Traffic Aggregation Point

Due to the recent explosive increase in the use of wireless-LAN-connected terminals, such as notebook PCs and tablets, in enterprise environments, communication quality degradations caused by wireless LAN (WLAN) often occur. There are two reasons for this. The first reason is the bandwidth is narrow compared to that of wired LANs. The second one is the traffic volume at the WLAN access point (WLAN-AP) is abruptly changed by terminal-device movements. However, previous measurement methods cannot clarify that the degradation occurs at a WLAN section or which WLAN section is the cause. There are two kinds of methods to measure communication quality including that of WLANs: end-to-end throughput measurement methods and wireless-layer quality measurement methods. The former cannot detect the bottleneck point; the latter cannot detect the degradation of TCP-layer quality, which represents the QoE (quality of experience). To solve the issue mentioned above, we developed a measurement method that detects the degraded WLAN section that is the bottleneck and measures the TCP-layer quality via the bottleneck. Our passive measurement method analyzes the RTTs (round trip times) of TCP connections. Based on the nature of TCP that its RTT continuously increases due to a bottleneck WLAN section, we detect degraded TCP connections. By referring to the information of a detected TCP connection and connection information collected from WLAN-AP, we can detect the WLAN-AP in the bottleneck WLAN section. We implemented our method onto our WLAN-quality visualization tool. Using this tool, we also applied our method to an enterprise network with over a thousand hosts. In this paper, we refer to hosts when they contain both wired and wireless LAN terminals. WLAN terminals are called terminals. As a result, our method clearly detected the WLAN bottlenecks in the enterprise network, and we confirmed our method was useful to solve WLAN-related issues.