HP has a handy new “feature” on some of their newer model home and office printers that allows you to print wirelessly when a wireless network is not available. The printer does this by broadcasting its own SSID with a name something like “DIRECT-B7-HP ENVY 4520 Series”. This seems like a harmless (and pointless) feature, but it can wreak havoc on your wireless network.
The issue with this feature is that the printer appears to only have one wireless radio, which is likely already connected to your wireless network using the channel your wireless access point or router is broadcasting. The printer then starts broadcasting a second SSID (the one mentioned above) on the same channel are your wireless network, essentially causing interference. This occurred at my house and at a customer site recently. My first thought at my house was to change the channels my router was broadcasting. After about 30 seconds, the printer switch to the same channel. You can set a static channel on the printer, but then you are unable to connect to your printer over the wireless network because it is listening on a different channel than you wireless network is broadcasting.
The solution is quite simple, all you need to do it disable Wi-Fi Direct Printing. AirPrint and wireless printing will continue to work with this feature disabled. To disable Wi-Fi Direct Printing do the following:
Details on HP Wi-Fi Direct Printing can be found here: http://www8.hp.com/us/en/ads/mobility/wireless-direct-printing.html
iOS 9 now will "help you out" by having the device switch to cellular data if it thinks your Wi-Fi connection is too slow. This could end up using more of your cellular data than you'd like. This appears to be turned on by default after the upgrade. You can turn it off by going to Settings -> Cellular then finding Wi-Fi Assist at the bottom of the screen.
I recently helped a customer having trouble with FaceTime and iMessage not working with his iPod touch. He was able to browse the web and get to the App Store, but the FaceTime and iMessage applications would not work. I connected my cell phone and was able to use FaceTime, a WiFi only application. I assumed this meant the problem was with his iPod, not his wireless Internet. However, his iPod worked correctly when he connected to a different wireless network. The problem fixed itself for about a week at his house, then started happening again. I did some reading and found that this could have been caused by DNS. I changed the DNS servers on his router to use different DNS servers. Immediately the problem was fixed.
Thinking back on my testing, I did not take into account that my phone could have been using 3G DNS servers during the first test. The lesson here is to be careful when using cell phones to test wireless connectivity.