Effect of coarse timer granularities on QoS guarantees in Unix based systems

While it is usually assumed that packet schedulers in routers have sufficiently fine-grain timers, network systems frequently have timers of coarse granularity. Therefore application users cannot obtain the desired QoS even if they reserve the required bandwidth for transmission. In this paper, we investigate QoS failures that occur due to coarse timer granularities. Based on the investigation, we experiment with two methods to cure the problems. We implement them in real PC Unix based systems and show that they can satisfy the QoS requirements of TCP connections by transmitting as much traffic as for the reserved bandwidth