comcast sped question

say does anyone happen to know how comcast or even other cable compains manage to throttle your modems? i had 100mbps and then i had to lower my bill so what they did was set me up into the same expact plan i had but under a new starter package. so then after they reset my modem it came back at 25 mbps. now for what i do this is fast enought as that is what i had a few years ago and they kept giving me more speed. but it has to be some program they send to the modem the must flash it into the speeds they want you to have.

i have a backup of the settings but i do not want to just restore that just yet if it will not do any good. jsut wondering if anyone happens to know if it is jsut the setting they change or is it a reflash they send out? if it would have been on ther end in there computer i'm not thinking they would have sent the signal to restart my modem.  thanks