Apple's AirDrop makes weird latency spikes for Wi-Fi wonks

"Visser presented his findings on Tuesday at the RIPE 91 conference, the biannual internetworking event organized by RIPE NCC, the regional internet registry for Europe, the Middle East and parts of Central Asia. In his talk, titled "Apple Wireless Direct Link: Apple's Network Magic or Misery," Visser explained that while using a new iPad he often encountered what he described as "very strange rhythmic stuttering" as he streamed audio to the device."

"He used the Moonlight streaming test tool to investigate and found 20 millisecond latency, but with a 25 millisecond variance he felt was oddly high for the uncontested environment that is a local network. He next used Steam's network testing tool, and found latency regularly bounced between three and 90 milliseconds. PING commands produced similar results, as did tests on different devices."

"At this point, Visser felt confident his hardware and applications were not the reason for his streams stuttering. Visser, who works at Japan's IIJ - Research La, dug into the situation and found AWDL constantly listens for requests to use AirDrop, and prefers to use certain "social" Wi-Fi channels - channel 6 for 2.4 GHz networks channels 44 and 149 for 5 GHz Wi-Fi."

Apple Wireless Direct Link (AWDL) generates continuous background traffic by listening for AirDrop requests and favoring certain "social" Wi‑Fi channels (channel 6 on 2.4 GHz; channels 44 and 149 on 5 GHz). This behavior causes Apple devices to periodically switch channels when not already on those channels, producing rhythmic Wi‑Fi channel swapping and measurable jitter. Testing with Moonlight, Steam network tools, and PING showed latency variance (about 20 ms with roughly 25 ms variance, and spikes between 3–90 ms). Disabling AWDL avoids the channel hopping and jitter but prevents AirDrop peer‑to‑peer functionality for Apple devices.

Read at Theregister