Feedback Control for Quality-of-Service Guarantees
A desirable behavior of a heavy-loaded Internet server is that the queueing delay of a request be proportional to its service time. Measuring quality of service in terms of slowdown is in line with the objective. Chapter 6 presented a queueing modelbased rate allocation scheme for proportional slowdown differentiation (PSD) on an M/M/1 server. This chapter revisits the problem in a general M/G/1 server model. The queueing theoretical approach provides predictable PSD services on average in the long run. However, it comes along with large variance and weak predictability in short timescales. This chapter presents an integrated feedback control strategy that adjusts the processing rate allocated to each class, according to measured deviations from the target slowdown ratios. It results in highly consistent PSD services in both short and long timescales.