Tamas Borsos

Cross-layer quality-based resource reservation for scalable multimedia

Resource reservation for Variable Bit Rate (VBR) multimedia streams is a complex task if both the requirements of service providers and of end-users need to be considered. In this paper we present a novel static reservation scheme for VBR multimedia traffic that takes into account the end-user Quality of Experience (QoE). We apply a two-step process for the reservation. In the first step, we map the target user-perceived quality to an upper limit on packet loss. The second step applies a numerical method, that uses a simple video model and a Markov queue model to determine the required bandwidth for the given level of packet loss. For the validation of the video and the system model we use simulation studies. Although our method is static, it is still able to capture the characteristics of a VBR multimedia, which is the main benefit.

On the temporal characteristics of video traffic

It is widely accepted that the video frame size process is long range dependent (LRD), which has been indicated by a number of statistical tests. This approach suggests the use of LRD traffic models for traffic engineering, which in many cases leads to subexponential queue tails in the network buffers. Basically, there are two concepts that are considered as the origin of LRD in video modeling: self-similarity and heavy tailed level durations. In this paper we argue for a new approach, where the frame size sequence is described by three processes representing three explicit time scales, all of them having a physical meaning. We demonstrate that this concept serves as an explanation for the outcome of the LRD tests. The properties that are attributed to long range dependence in fact seem to be the result of non-stationarity of the large time scale process. We also show that the high frequency component is short range dependent, thus questioning the presence of long range dependence in video traffic.

A Measurement Based Solution for Service Quality Assurance in Operational GPRS Networks

Measuring data and signaling traffic in an operational network may prove to be a better basis for dimensioning than earlier approaches based on simulation models or analytical calculations. Dimensioning rules based on an ongoing measurement process are expected to adapt automatically to changes in traffic statistics and network parameter settings. In an operational cellular network cell load shows diurnal as well as spatial variations. If we look at different cells over time or at cells located in distant geographical areas, we find cells serving varying numbers of subscribers and carrying varying amounts of circuit switched and packet switched traffic. The idea is to capture all user transactions over a large geographical area, determine the traffic load during these user transactions at cell level, and calculate the quality of service measures of interest for the transactions. If samples are collected at different traffic load levels, and we depict the obtained quality of service measures as a function of the traffic load, the resulting graph gives a dimensioning curve. We present a methodology for obtaining cell dimensioning charts based solely on traffic traces available in all operational GPRS networks, and we provide new insights into the performance of the GPRS system by analyzing a month long measurement trace captured in a live network using the new methodology.