Supporting Excess Real-Time Traffic With Active Drop Queue

The requirements of real-time applications mean that they often stand to benefit from network service guarantees, and in particular delay guarantees. However, most of the mechanisms that provide delay guarantees do so by hard-limiting the amount of traffic the application can generate, i.e., to conform to a traffic contract. This can be a significant constraint that conflicts with the operation of many real-time applications. Our purpose is to propose and investigate solutions that overcome this limitation. Our four major goals are (1) guarantee a delay bound to a contracted amount of real-time traffic; (2) transmit with the same delay bound as many excess real-time packets as possible; (3) enforce a given link sharing ratio between excess real-time traffic and other service classes, e.g., best-effort; (4) preserve the ordering of real-time packets, if required. Our approach is based on a combination of buffer management and scheduling mechanisms. We evaluate its "cost" by measuring the overhead involved in an actual implementation, and we investigate its performance by simulations using video traffic traces.