For year and half 5510 operates just fine, then it has abruptly slowed by a factor of 10. When on the line the ping times are in the 400 ms range, when off or very lightly loaded in the 18 ms range. DSL provider has changed equip and lines but same thing. running a 9K packet count with nearly 500 dropped. The 5510 is at the main office and 7 501s connect to it over various broadband technologies, regardless of distance still get (at times 450 ms) long round trip times only when 5510 is on line.
I have this problem too.