Network Quality of Service Measurement System for Application Requirements Evaluation

We have designed and implemented a system that permits the measurement of network Quality of Service (QoS) parameters. This system allows us to objectively evaluate the requirements of network applications for delivering user acceptable quality. We use FastEthernet taps to monitor full-duplex traffic and programmable network interface cards to extract all the information needed to compute the network QoS parameters: latency, jitter, packet loss and throughput. The measurement system makes use of a global clock to synchronize the time measurements in different points of the network. We have employed this system to evaluate the performance of several network devices and study the behaviour of real network applications, such as file transfer and voice over IP. For these applications user perceived quality (UPQ) metrics have been defined in order to assess their QoS requirements. Since we measure simultaneously network QoS and application UPQ, we are able to correlate them. Determining application requirements has two main uses: (i) to predict UPQ for an application running over a given network based on the corresponding measured QoS parameters and understand the causes of application failure; (ii) to design/configure networks that provide the necessary conditions so that an application will run with a desired UPQ level.