Typically, throttling means to take two connections and distribute the load between them so that the faster connection always gets the most load, or to limit bandwidth for specific clients. I think you're idea falls roughly into the second category. Since I can't think of a better name for it, calling it "throttling" is good enough for me
I know throttling can be done in linux. I, personally, haven't done it. But I don't know if you really need to do any throttling given the situation you described.
On an Ethernet network, every computer gets whatever bandwidth it can grab. So, if you have one system that needs 512/256kbps, and another system that needs 1024/256kbps, both will probably get their bandwidth. If you then have a third system that needs 120/230kbps, then suddenly everyone's bandwidth goes down to accomedate the load. Throttling would come in when you need to tell the second system to only use 512kbps instead of 1024 -- since it would be hogging the connection.
If I am understanding what you're saying correctly, what you're trying to do is distribute bandwidth by request -- so, one system requests bandwidth for X amount of time and gets that full amount of bandwidth (leaving a static pool of bandwidth for unrequested access as described above). That being the case, I don't know of anything built into the IP protocol that would specifically do this. It's not a native feature, so while there isn't any technical reason it couldn't be done, anything you do would probably have to be written yourself.
You may also want to consider that if you have a linux box between the network and the DSL router, nobody is actually getting access to the DSL router. Everyone is instead accessing the linux box which is routing information to/from
the DSL router. So, really, nobody has a need to have access to the DSL router, they all just want a route for information to go across the internet. This being the case, what you probably really want is a router
. Your wireless router has that built in, so you really don't need the linux box there in order to share the internet connection.
Give it some thought. Nothing solid here, just food for thought. Let me know if any of this sounds like what you're trying to do and we can go from there