Due to the complex diversity of contemporary Internet services, computer network measurements have gained considerable interest during the recent years. Computer network measurements supply network research, development and operations with data important for network traffic modelling, performance and trend analysis etc. Hence, the quality of these measurements affects the results of these activities and thus the perception of the network and its services. Active measurements are performed by injecting traffic into a network and observing the treatment that this traffic receives. Usually, active measurements are perfomed by writing special applications that act at sender and receiver. These applications are usually executed as user processes. This causes some concern since this can have serious implications on the obtained results, as they are affected by the scheduling mechanisms in the operating system. In this paper, we evaluate the accuracy of two active measurement tools, ping and J-OWAMP, by using high accuracy passive measurements. Our results show that ping is quite accurate, to 0.1~ms for Linux and 1~ms for Windows~XP, while J-OWAMP has a discrepancy of 25~ms plus serious time synchronization problems.

Noggrannheten på Ping och J-OWAMPs resultat utvärderas.