Taking this model of QoS management, including its extension to cover all resources, gives rise to the following requirements:
The first of these requirements can be met by what we have called the QoS manager. This runs occasionally as requests to change the allocation of resources are made. It does not run for any other reason and, to borrow a phrase from communications, can be said to run out of band with respect to the application computation.
The second and third of these requirements are strongly related. Both are concerned with in band application computation and, again to use the language of communication systems, lead to a philosophy of a low level multiplexing of all resources within the system. This consideration gives rise to a novel structure for operating systems.