Different Granularities

Abstract

As described in Chapter 2, one phenotype facet of a network QoS systems is its granularity. The granularity of a network QoS system determines its capability to differentiate between units of service. Fine-grained systems provide assurances about QoS for units like application flows whereas coarse-grained systems only provide assurances at an aggregate level of traffic. In heterogeneous QoS systems with differing granularities between the individual QoS systems, there is a clear need for mediation between these different granularities. Overlaying a coarse-grained system onto a fine-grained system is generally simple but the other way around, i.e., supporting fine-grained QoS assurances over a coarse-grained QoS system is a challenge. The general technique for an edge device to apply to the latter situation is called aggregation. Note that by aggregation we refer to the gathering of units of service in the spatial domain in contrast to an aggregation in the time domain as it is dealt with in Chapter 5. In this chapter, we concentrate on the aggregation of deterministic service flows as these can be assumed a particularly hard case. Furthermore, we believe that there is always a need for deterministic services by some applications.