Web Workload Generation According to the UniLoG Approach

Generating synthetic loads which are suffciently close to reality represents an important and challenging task in performance and quality-of-service (QoS) evaluations of computer networks and distributed systems. Here, the load to be generated represents sequences of requests at a well-defined service interface within a network node. The paper presents a tool (UniLoG.HTTP) which can be used in a flexible manner to generate realistic and representative server and network loads, in terms of access requests to Web servers as well as creation of typical Web traffic within a communication network. The paper describes the architecture of this load generator, the critical design decisions and solution approaches which allowed us to obtain the desired flexibility

Efficiency of PET and MPEG Encoding for Video Streams: Analytical QoS Evaluations

this paper we introduce analytical models which allow us to determine the expected frame loss probability of MPEG encoded video streams assuming communication via constant bit rate (CBR) virtual circuits with data losses and/or unrecoverable transmission errors. The models can be used to compare the quality-of-service (QoS) as observed on Application Layer for encoding schemes without and with forward error control, possibly making use of different prioritization of transmitted data units (in particular applying PET encoding algorithm as designed at ICSI). The models are applied in various case studies to compare the efficiency of the error control schemes covered. *) research during sabbatical leave from: Computer Science Department, Telecommunications and Computer Networks Division, Hamburg University, F.R.Germany

A Validated Analytical Model for Availability Prediction of IPTV Services in VANETs

In vehicular ad hoc networks (VANETs), besides the original applications typically related to traffic safety, we nowadays can observe an increasing trend toward infotainment applications, such as IPTV services. Quality of experience (QoE), as observed by the end users of IPTV, is highly important to guarantee adequate user acceptance for the service. In IPTV, QoE is mainly determined by the availability of TV channels for the users. This paper presents an efficient and rather generally applicable analytical model that allows one to predict the blocking probability of TV channels, both for channel-switching-induced, as well as for handover-induced blocking events. We present the successful validation of the model by means of simulation, and we introduce a new measure for QoE. Numerous case studies illustrate how the analytical model and our new QoE measure can be applied successfully for the dimensioning of IPTV systems, taking into account the QoE requirements of the IPTV service users in strongly diverse traffic scenarios

Dynamic Resource Reservation and QoS Management in IEEE 802.11e Networks

Quality of service (QoS) guarantees are becoming increasingly relevant for mobile networks, too, as they have to support, e.g., more and more audio and video applications with real-time requirements. Therefore, recent extensions of WLANs, namely IEEE 802.11e, are introducing new mechanisms to enable the provisioning of QoS guarantees, in particular by means of resource reservation. This paper suggests to diminish the inefficiencies of the resource reservation approach as taken by IEEE 802.11e. The solution advocated is to embed the authors’ earlier abstract approach for a dynamic resource redistribution into 802.11e based WLANs. By means of analytical and simulation models it is demonstrated that the extension of 802.11e based networks by a dynamic resource redistribution can lead to a significant increase in overall network utilization, though QoS requirements can still be guaranteed.

SUMMARY

An important means to guarantee an acceptable quality of service in networks with real-time communication requirements is the reservation of resources at connection setup time. However, such reserved resources, e.g. transmission bandwidth, may be unused as a consequence of the variations in the actual resource demands. Therefore, a more efficient resource utilization is possible if communicating stations or end-users dynamically hand over some of the free resources temporarily to the other communication partners, e.g. of a “broadcast network”. This paper concentrates on two fundamental problems of such a demand-based sharing of resources: on the one hand, estimation of the current resource requirement on the basis of load measurements is investigated and, on the other hand, we elaborate efficient algorithms for resource sharing respecting real-time requirements. The algorithms proposed for load estimation and for resource sharing are evaluated analytically with respect to their efficiency for worst-case, average-case and realistic load scenarios. Our approach suggested for resource and traffic management allows one to achieve significantly better utilization of network resources. Copyright c ○ 2000 John Wiley & Sons, Ltd