When configured correctly in a network QOS can be a wonderful thing. The ability to prioritize network traffic by it’s importance is crucial in most places that use VoIP systems to ensure that normal network traffic doesn’t kill off telephone calls. QOS can be both difficult to configure and simple depending on what systems you use and is being used in industry around the world.
With VoIP moving to home users now problems occur with keeping calls going when other home users are download or the like. Newer modems support QOS but still suffer from a simple flaw which impacts the usefulness of it. These modems can only control QOS for outgoing packets (uploads) and not incoming, becuase the QOS needs to be done on the ISP switches/routers. This flaw means that if someone packet floods your connection, QOS won’t be able to help your VoIP system.
There isn’t really a simple fix to this, however it would be nice if ISPs had a configuration page or the like to allow you to make simple QOS rules. Some people will want QOS on VoIP IPs/ports and others will want it on other services.