Statistical Quality of Service Assurances Using Probabilistic Envelopes

Recent work in the area of statistical QoS has demonstrated that a) statistical envelopes can lead to large gains in utilization, b) easily enforced deterministic envelopes can be used to obtain such statistical envelopes, c) end-to-end performance bounds can be provided with high utilization targets if rate-controlled scheduling disciplines are employed on every node. In this paper we examine achieveable performance bounds without the per-node specialized scheduling, for a feedforward network. Employing enforceable statistical envelopes to bound traffic entering a network, we examine techniques to compute the envelopes at an arbitrary node inside the network by using existing results on per-hop burstiness increase. Given a delay target the probability of delay violation is computed for an end-to-end performance bound. We then examine ways to set delay targets at individual nodes so that a) the delay targets and violation probabilities can be derived without an exact traffic description, b)the network can provide meaningful end-to-end delay assurances, b) the provider can set a target utilization constraint and quantify the tradeoff in terms of delay violation probability. Thus given a network without any specialized schedulers per-hop, but strict admission control, we demonstrate that reasonable utilization levels can be attained, while providing assurances on QoS parameters. The utility of the proposal is illustrated with an example feedforward network using numerical simulations.