The wifi speed depends on the link speed between the router/extender and the devices. So it will be better if you can check the link speed on your phone when it is connected to the router and when...

The range extender will have the same authentication type with the router, so if your router uses AES, the extender should be the same. So if your main router is AES, then the 850RE should be AES as...

Did you refer to this link to set parental control? http://www.tp-link.com/en/faq-1389.html It will be helpful if you can share the settings page on the router, or you can send email to...

What is the previous firmware? It seems the 170111 is the special firmware for JP, if your previous firmware is universal, then it cannot be downgraded. BTW, when it drops connection, how about the...

You need to disable QoS on the router first, go to Advanced > QoS and make sure it is not enabled.

Which kind of VPN do you want to connect? Go to Advanced > Network > Internet, you can choose PPTP or L2TP for Internet Connection Type, then you can connect to your VPN server.