It doesn't necessarily mean that it's what causing your problem though.
I had a similar problem at one point, and it turned out to be something on their network acting up. I'm not sure what exactly. Try to get a priority tech out there during the times the problem happens, they can get things fixed quickly.
Also, I hope you mean 0.5 Mbps, and 1.8 Mbps up, not Kbps.
