Different Time Scales

Abstract

In this chapter, the second phenotype facet of network QoS systems, the time scale of the system is under investigation. To recapitulate (from Chapter 2), the time scale of a network QoS system is its speed of reaction to individual requests for differentiated treatment of units of service. A slow time scale system will prefer requests to arrive with a low frequency and persist unaltered for a substantial period while a fast one is able to support much higher arrival rates of requests and is thus more amenable for short-lived units of service. Obviously, when overlaying a slow time scale QoS system over a faster one, there is no problem. However, and that is a more likely case, for the overlay of a fast time scale system on a slow one, there is a mismatch to be mediated at the edge between the two. The technique that is applied at an edge device for this mediation is called decoupling of time scales. Decoupling can also be viewed as aggregation of requests in time in contrast to the aggregation in space treated in Chapter 4.