Reliable Monitoring of Network-related Performance Parameters inWireless Environments

Abstract

End-to-end delay estimation is a crucial issue in the design of network monitoring systems for wireless best-effort infrastructures. This work demonstrates that estimations based on one-way delay are the most suitable for evaluating the delay on wireless networks such as Wi-Fi LANs andBluetooth piconets. To prevent delay measurement from being affected by clock synchronization issues, raw measures need to be corrected by estimating clock synchronism attributes such as clock skew and offset. However, due to network noise and clock adjustments, this estimation process may affect the reliability of network monitoring systems. In this paper we propose a trustworthy network performance monitor designed to support adaptive and/or soft real-time applications in wireless environments. The monitor corrects one-way delay measurements through an on-line algorithm for evaluating clock synchronism attributes. Simulation experiments show the effectiveness of our approach. RationaleWe are witnessing an increasing interest on the so-called next generation of distributed mobile applications, such as tele-conference, tele-presence, and tele-control. These applications are characterized by soft real-time requirements, and they are typically deployed over hybrid infrastructures, encompassing wired as well as wireless technologies (e.g. * This work has been partially supported by the Italian Ministry for Education, University and Research (MIUR), within the framework of the FIRB Project "Middleware for advanced services over large-scale, wiredwireless distributed systems (WEB-MINDS), and by the Regione Campania, within the framework of the "Centro di Competenza Regionale ICT". Wi-Fi [3], Bluetooth [1], UMTS [2]). Due to the best effort policy of current wireless technologies, it is crucial to realize reliable monitoring systems in order to provide applications with feedback for adaptivity to network changes [8,13]. To this aim, network monitoring systems must be accurate, since errors in the network performance estimation could lead the application to erroneous behaviors.A plenty of research studies has been conducted to estimate performance of Internet. The ITU-T [7] recommended network performance parameters (end-to-end delay, delay variation, and information loss) to be used for QoS estimation in IP-based networks. Several algorithms have been proposed for addressing issues in end-to-end delay estimation, the crucial parameter from which the other network performance indicators can be derived. Two are the most common metrics: i) the Round Trip Time (RTT); and ii) the One-way Transit Time (OTT). Asymmetric paths affect delay estimations based on RTT, whereas clocks synchronization affects delay estimations based on OTT. Although RTT is a good estimation of end-to-end delay in traditional LANs (such as IEEE 802.3x), we experience that it does not represent the favored choice for performance estimation of wireless environments, such as WLANs and Bluetooth piconets. As for the OTT, approaches for the correction of raw measures include...