Measuring WCDMA and HSDPA Delay Characteristics with QoSMeT

Quality of service (QoS) is becoming increasingly important with the rise of multimedia applications (e.g., voice over IP (VoIP), video conferencing, online gaming, and Internet protocol television (IPTV)) in public data networks. These applications demand real-time service, while the networks should still be able to transfer also other traffic reliably (e.g., data, e- mail, WWW). We have developed a measurement tool, which is able to measure one-way QoS performance statistics. The tool enables passive monitoring of the desired application(s) and gives information about the QoS provided by the network. The tool can be used practically over any kind of network structure as long as IP is supported. In this paper, we focus on detailed end-to-end delay characteristics measured in live HSDPA (high speed downlink packet access) enabled 3G network. HSDPA provides clearly better delay performance than the basic WCDMA (wideband code division multiple access). Interestingly, deterministic long time behavior in delay was observed, and also, discrete jitter levels were found. With argumentation, and finally with a trial, we proved that these phenomena originate from the CBR-type (constant bit rate) VoIP source traffic affecting with 3G network timing mechanisms and mutual clock drifts. As a side product, the study also showed that it is advisable to verify the operation of traffic generation tools before using them.