I had the same issue before with ER6120, I contacted tech support and they said when there is NAT device between client PC and ER6120, the ER6120 won't response, maybe it's a bug, and the technical...

In a word, PPPoA is PPP over ATM, you need ADSL modem to dial up the PPPoA connection, you have to buy ADSL modems for each line.

That's wrong, I can tell the answer from TP-LINK engineer is for TL-R470T+, not TL-ER5120. I'm pretty sure that the maximum rule of Policy Routing for TL-ER5120 is 64.

That's impossible, iphone can't work as 3G modem.

I'm pretty sure TP-LINK wired routers support NAT Loopback, I have test it with my IP camera, it works.

TL-WR740N does not support telnet or ssh