said by Chuck kCAR :The st516 is a piece of garbage. If you're lucky enough to get one that actually outlasts the warranty period it's a miracle.
The ST516 its self is fine and very reliable.
The power supply's for the ST516... now that's a whole other story.
The included 18V AC adapters make the modem run very hot and unstable, I found myself needing to powercycle mine frequently. (The power light would turn red and it would stop working).
I switched to a omron 24V PSU (with adjustable pot so I can lower it to 22V to match the DC requirements of the modem). My ST516's haven't even needed a reboot since I did that. (many months ago) I reccomend everyone does this.
They barely even get warm to the touch now too, before the left side of the modem got frighteningly hot.