Zapping Wi-Fi Performance
Reflections, refractions, signal fading and attenuation all wreak havoc on throughput causing performance to vary freakishly.
Because wireless performance is inherently statistical, accurate performance testing must account for this random component.
Here's a good Black Paper on "Characterizing Wireless Performance" written by one of our super geeks (apologies in advance).download it here.
Ultimately, real-world wireless testing is essential, but this testing must be performed in a way that exposes the underlying performance statistics, looking beyond average throughput.
Sampling is the key to recovering the statistical performance and must be conducted across all relevant dimensions. Time-based sampling of the wireless channel, sampling at a large number of locations and sampling across the full range of channels are the keys to providing valid comparisons and predictions.
Zap is a wireless performance testing tool that Ruckus engineers developed precisely for this purpose. While Chariot and NetPerf are good tools for determining average (50%) throughput, they are expensive and don't do the best job in sampling to the 99.5 percentile.
Zap works by sending controlled bursts of packets and measuring both packet loss and inter-arrival times. The primary results reported are number of packets lost, total packets received and detailed throughput statistics. Because Zap provides a measure of both throughput and consistency over time and distance, it has particular importance to streaming video, voice and other latency-sensitive applications. Conversely, knowing only average throughput levels will not help predict the performance of a wireless network. By measuring the maximum throughput of batches of packets, Zap is able to determine the minimum throughput that can be expected at a given percentile
We initially developed Zap to as a way to figure out worst case performance for multicast IPTV streaming. Service providers just don't care about average throughput, they care about what they can guarantee - what they can charge for. For Ruckus, Zap has been invaluable making our Wi-Fi products perform better. With it, we've been able to effectively guarantee how they will perform 99% of the time in a given area (just don't hold us to it).
Zap lets any company better understand the statistical throughput distribution of a wireless system to more accurately characterize Wi-Fi performance. With Zap, admins can easily test sustained throughput of an existing system and predict the real-life performance of a planned system before deployment.
By enabling an accurate determination of the true, sustained and worst-case performance that a wireless network can deliver 99.5 percent of the time, companies can become more confident in knowing that their wireless network will adequately support the more stringent application requirements that exist and the quality of service that users have come to expect.
Now in our infinite wisdom, we are releasing Zap to the world. We've released the raw code to open source and have posted compiled versions for the PC (Download Zap_install_20100413) and the Mac (download Zap_mac_20100111) to anyone who wants to use it.
NOTE: The ZapD file is a daemon that runs on the server, the other Zap file runs on the client.