Design trade-offs for networks with soft end-to-end timing constraints

As broadband capabilities on wired, wireless and mobile phone networks proliferate, real-time multimedia traffic is expected to consume higher portions of the available bandwidth. Usage models in such networks range from low-cost VoIP to high-cost, high-quality, high-resolution video streams along with many intermediate data streams. Video flows, however, have stochastic processing requirements, and they may result in very low utilization levels if traditional real-time scheduling techniques are used. This calls for new analytical methods. In this paper, we illustrate a set of new techniques for reasoning about the lateness of such stochastic flows, and apply it to engineer a wired multihop real-time network. We make use of 4 dominant parameters to characterize the design space: end-to-end deadline, acceptable lateness, the number of hops and the network workload. Given any three of these parameters, the remaining parameter can be computed. For instance, if a stochastic flow passes through 10 nodes, its end-to-end deadline is 150 ms, and no more than 0.1% of the packets can be late, what is the maximum allowable system workload that would satisfy the lateness requirements? This maximum allowable workload can then be used to develop for the admission control policy to guarantee that the specified timeliness requirements are met. This paper provides insights into real-time network effects and rules of thumb to properly engineer a high utilization real-time EDF (earliest deadline first) network. Simulation and experimental results validate our methods. Our techniques are further applicable to heterogeneous network cases where some nodes on the flow path are bottlenecks or have cross traffic from other flows.