For years Apple had been using a networking routine by the name of mDNSResponder which had proven rather reliable (not perfect) and had minimal issues. This routine was still in use in iOS 7 and OS X Mavericks. With the advent of iOS 8 and Yosemite, Apple deployed a new routine by the name of DiscoveryD, DD for short. While most users did not experience any issues with DD, a large subset encountered substantial Wi-Fi difficulties and some of those proved to be rather serious - inability to connect at all, repeated disconnects, very short Wi-Fi range, etc. Our 4 iOS devices (2 mine, 2 my wife’s) were part of that subset that encountered issues. My devices were paired with an up-to-date, high-end Cisco router (latest firmware). They did not experience connection or range issues, however my download speeds were severely degraded right after updating to iOS 8 rendering my iPads and iPhones rather useless at home. After taking the usual Wi-Fi "repair" steps I discovered that turning Bluetooth and AirDrop OFF restored my download speeds on all my iOS devices to full ISP range. Interestingly, my MacBook Pro, my two Dell PCs and an old Toshiba PC all maintained full download speeds regardless of Bluetooth setting (and in the case of the Mac, AirDrop being on or off). Simply, the iOS devices could not be used with BT/AD on, while all non-iOS devices had no issues at all. My difficulties were minor in comparison to others, I just left BT and AD off, turn them on only when AirDropping, and then turned them off again, a hassle but not a major issue.
I have posted on this thread many times before and as a result I received two calls from AppleCare earlier this year. Apple collected various logs from my iOS devices and took extensive information regarding my Wi-Fi configuration. The calls lasted over one hour each. Several others have reported the same. Apple was well aware that there were issues with DD and had been trying to address them. In fact, iOS 8.3 included various "fixes" for Wi-Fi and Bluetooth, see the release notes here: iOS 8.3 Those fixes worked for some but not others - they did not work for me.
When Yosemite 10.10.4 came out on June 30, users noticed that Apple had abandoned DD and had switched back to mDNSResponder - easy to test with Activity Monitor on a Mac. Apple’s 10.10.4 release notes stated “improvements to Wi-FI”. Apple attempted to "fix" DiscoveryD but after 9 months of effort they opted to revert back to mDNSR instead, albeit with some tweaks from the older version. Apple did not do this lightly or for the "fun" of it, they did so because they were well aware that many users were having problems indeed and their attempts to fix DD had proven unsuccessful. While there will always be Wi-Fi issues reported for any iOS, Androids, Macs or PCs (and now iOS 9), the general consensus from technical publications and affected users is that reverting back to mDNSResponder in Yosemite has significantly reduced the problems encountered with the previous routine.
I am now pleased to report that DiscoveryD has been replaced in iOS 9 as well. This was not unexpected as they had done so for OS X as mentioned above. Yesterday afternoon I updated my iPad to iOS 9 and I am also pleased to report that after a year of waiting my Bluetooth / AirDrop issues are finally over. I encountered no issues with the update whatsoever. My ISP nominal download speed is 15 Mbps. My iPad consistently received that speed as long as BT and AD were off. With BT / AD on my iPad crawled down to less than 1 Mbps, sometimes much less. After updating to iOS 9 I turned BT and AD on and began testing with OOKLA. I have yet to receive a DL of less than 14.9 (yesterday and today) regardless of the fact that BT / AD are now ON.
I updated my iPhone late last night and I am also pleased to report that the issues have been resolved for the phone as well. Prior to updating, i.e while still running iOS 8.4.1, I did 5 OOKLA tests with BT and AD turned ON. The 5 tests can be seen on the first screenshot below. They average 0.6 Mbps. After updating to 9, the iPhone also delivers full speeds regardless of BT and AD now being ON. The second screenshot shows 5 additional OOKLA tests performed after the iOS 9 update. They average 15.15 Mbps. This morning I did an additional 5 tests and they average 15.14 Mbps. Goodbye DiscoveryD, welcome back mDNSResponder!!!
I hope other users have similar success with their updates as well. Good luck to all. 🙂
