Voice over IP (VoIP) is gaining an ever increasing popularity. As such, it nowadays represents one of the most studied test applications in the performance evaluation of wireline and wireless networks. However, a sound performance analysis of VoIP communications should be carried out at the user level, by computing perceptive metrics like the Mean Opinion Score (MOS) or the E-Model. In this paper, we present enhancements to the popular Network Simulator 2 (ns-2) that allow a reliable VoIP user-level performance analysis to be carried out through simulation. We show that computing performance measures at the IP level, which is usually done in ns-2, often leads to inaccurate results. Our code
Reduced energy consumption is a crucial aspect of mobile Broadband Wireless Access (BWA) networks, which are expected to be populated by battery-operated devices, like mobile phones and palmtops. For this reason the IEEE 802.16e specifies a set of power saving mechanisms to be employed by the Base Station (BS) and Mobile Stations (MSs) to concurrently reduce the amount of time the latter have the wireless interface on. The mechanisms are classified into three classes, which are designed for different types of applications. In this paper we focus on class I, which fits the typical requirements of best-effort traffic. With class I, an MS with power saving enabled alternates between sleep and listening periods. The duration of the sleep periods increases by a factor 2 each time a listening period ends, up to a maximum sleep window size. Since the standard does not provide guidelines for setting the above parameters, which are negotiated between the BS and MSs when setting up a power saving class, we evaluate via simulation their impact on the performance, in terms of both application-specific metric, i.e. delay or throughput depending on the type of traffic, and the amount of energy saved.
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