The quality of my VoIP phone calls suffered whenever I was downloading or uploading anything. This was irritating, especially for those calling me (I heard them better than they heard me). So I poked at Iproute2 and other howtos, especially with regard to VoIP traffic, but I couldn't find anything that worked well. After some playing around, I've found settings that were right for me: consistant VoIP quality, regardless of any activities on the wire.