It uses same downloader SL does (+pool system).Forboding Angel wrote: SD has it's own subset of problems. The most notable being downloads that eff up halfway through or never start to begin with, or SD kicking the user from the battle if the map refuses to download.
Failed downloads are simply not available/not registered correctly, newbie user should not be bothered to download stuff manually.
Downloads that halt in middle are those with dependencies,where dependency is defined using archive name and not internal name, or is simply unavailable. Those can fail in middle. I have never seen or received report of non-dependency download stopping in middle since SD became lobby.