Analysis of Shared Memory Priority Queues with Two Discard Levels

Two rate SLAs become increasingly popular in today¿s Internet, allowing a customer to save money by paying one price for committed traffic and a much lower price for additional traffic which is not guaranteed. These type of SLAs are suggested for all types of traffic from best effort to QoS constraint applications. In access networks, where these SLAs are prevalent, shared memory switches is a common architecture. Thus, dimensioning and management of shared memory queues for multiple priorities each with two levels of guarantees becomes an interesting challenge. We present a simple analysis of a multipriority multi discard level system controlled by a buffer occupancy threshold policy aimed at assuring service level agree- ment compliance for conforming (i.e., committed) traffic, and performance maximization for non-conforming (i.e., excess) traffic. Our analysis shows how the different system parameters: total buffer size, threshold position, and offered load control performance for the committed and excess traffic. Our results allow assuring high service level agreement compliance for conforming traffic, and performance maximization for non-conforming traffic.