Several users have reported slower Wi-Fi Internet throughput after the update to iOS 4.2.1. This issue may be due to a change in power delivery/draw (which also appears to be causing the “Cannot Use Device. The connected USB device requires too much power” error).
Change DNS servers. This problem can often be solved by simply changing DNS servers. On your iPhone, while connected to a Wi-Fi network, follow these steps:
- Go to Settings > Wi-Fi
- Tap the blue arrow next to the currently connected Wi-Fi network
- Tap DNS, then delete the current entries and enter the following: 126.96.36.199, 188.8.131.52 (or you can try Google’s public DNS servers: 184.108.40.206, 220.127.116.11)
- Tap return
Turn router off then on Try turning your wireless router off then back on.
Change or turn off wireless security You may want to try toggling the settings on your wireless router, switching from WPA to WEP or vice versa, or, as a last resort, turning wireless security off altogether. For AirPort routers, this can be accomplished with the AirPort Admin Utility. For other routers, this can usually be accomplished by accessing the router’s configuration page — open a browser and enter the address 192.168.1.1.
Reset network settings on iPad. On your iPad, open Settings, then navigate to “General” in the left-hand pane. Scroll down and tap Reset, then select “Reset Network Settings.” This will delete any stored WiFi passwords and other information, but may result in a more stable connection.
Adjust brightness upward. Oddly, a number of users have found that they can resolve this issue by simply adjusting the iPad’s brightness level upward and off the lowest setting. To do this, tap Settings, then select “Brightness & Wallpaper” from the left-hand pane. Slide the brightness bar upward, then wait 1-2 minutes and check for an improvement in signal strength. Speculation holds that a power delivery issue associated with the screen brightness affects Wi-Fi.
Change thresholds in router settings. Access your routers configuration screen (for most routers, open a browser and enter the address 192.168.1.1), then change the fragmentation threshold and the CTS/RTS threshold as described here. Some users have found success with the settings Fragmentation= 2048, RTS = 512.
Change 802.11 spec on router. Try changing your router’s wireless spec mode from B, G and N to G only or vice versa. For AirPort routers, this can be accomplished with the AirPort Admin Utility. For other routers, this can usually be accomplished by accessing the router’s configuration page — open a browser and enter the address 192.168.1.1.
Switch routers. Although a far-from-ideal solution, some users have found success with switching to a different wireless router.
Turn off “Ask to Join Networks.” To do so, tap Settings on your iPad, then select “Wi-Fi” from the left-hand pane. Slide “Ask to Join Networks” to off. Speculation holds that leaving this option on causes the iPad to constantly seek networks, resulting in some type of interference with the network to which it is connected.
Forget network then rejoin. Tap Settings on your iPad, then select Wi-Fi from the left-hand pane. Choose the network with which you are experiencing difficulty, then select “Forget this network.” Go back to the previous screen and rejoin the network.
Turn off Bluetooth. Some users report that, perhaps due to interference issues, turning off Bluetooth can boost Wi-Fi signal strength. To do so, tap Settings then tap General in the left-hand pane. Tap Bluetooth in the right-hand pane, then slide to off.