It is normally 1/8th of the internet plan you choose...but i might be wrong.
May be it is right, but I remember that when I was using the same broadband carrier some years back at 1MBPS unlimited, and when IDM was not available for me, the d/l transfer speed was usually around 85~100kbps consistently. that means, the IDM isn't giving me too much of d/l speed advantage over the default one, but whatever gets the thing done in a faster way is OK it seems...

Anyway, Indian broadband speed consistency(!!) is no where compared to what it should actually be imo.
They might say that are offering 4mbps, but no one has really tested their word and at different times and different conditions...
In my town, the BSNL is down almost every alternate day, and sometimes for 8~8 days continuously! Once I visited the bank branch, and the manager, a family friend, was fuming because the bank's BSNL network was down for a week, and BSNL wasn't prepared to even tell him how long this would continue...
IMO, Airtel gives a steady performance, and may be Vodafone comes 2nd best or equal in my region. But Docomo, BSNL are best avoided.... better not to have internet at all, if those 2 are your only options. lol