I want a strange one. Manage network access priority at the application level within the same system.

Sometimes there are strange desires. Now I want to find some application that would allow setting the priority for network access for programs running on my computer.

The goal that I want to achieve with such a program is quite simple and I will explain it with an example. Imagine that µTorrent is running from me and, hard biting into the channel, it pumps ... well, let's say a fresh image of Debian. Shakes so that the entire channel under the download and takes. At the same time, Thunderbird is launched, which checks the boxes once again and stumbles upon an immense letter with important documents on work. And µTorrent and Thunderbird begin to fight for the channel outside, and no one is going to give in: both the first and the second are trying to get the most out of what is available to them. As a result, the speed is divided, do not understand as the loading of documents has to wait because the not so important film image swings.

But if there was a priority management system that I dream about, then it would be possible to configure in it that µTorrent can wait and send / receive data in case something happens (that is, it has a low priority), but Thunderbird should not wait should never and if necessary, the entire available channel should be given to it (maximum priority).
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Perhaps such a system already exists and is even available as freeware or even open source (plus it also works in Windows Vista), but I don’t know what to look for and where in Google. Therefore, I will be glad to any tips, well, or a tub of cold water on my head, so that I dreamed less.