Sinisa Srbljic

Scalable and Accurate Prediction of Availability of Atomic Web Services

The modern information systems on the Internet are often implemented as composite services built from multiple atomic services. These atomic services have their interfaces publicly available while their inner structure is unknown. The quality of the composite service is dependent on both the availability of each atomic service and their appropriate orchestration. In this paper, we present LUCS, a formal model for predicting the availability of atomic web services that enhances the current state-of-the-art models used in service recommendation systems. LUCS estimates the service availability for an ongoing request by considering its similarity to prior requests according to the following dimensions: the users and services geographic location, the service load, and the services computational requirements. In order to evaluate our model, we conducted experiments on services deployed in different regions of the Amazon cloud. For each service, we varied the geographic origin of its incoming requests as well as the request frequency. The evaluation results suggest that our model significantly improves availability prediction when all of the LUCS input parameters are available, reducing the prediction error by 71 percent compared to the current state-of-the-art.

Formal definition of SIP proxy behavior

The rapid growth of the Internet has made possible the use of multimedia in WAN communication. In order to control multimedia sessions between users, the SIP protocol was introduced. The original definition of the SIP protocol is given in the form of a RFC document that contains a number of implementation and compatibility problems. In order to formally define the SIP protocol and thus remove the implementation and compatibility problems, we present the behavior automata for SIP proxy systems. Since the automata are defined in UML, they can be directly used with software tools that translate UML specifications into high-level language code (eg, C++, Java). Results presented improve the implementation time and compatibility for SIP proxy systems.

Prediction of atomic web services reliability based on k-means clustering

Contemporary web applications are often designed as composite services built by coordinating atomic services with the aim of providing the appropriate functionality. Although functional properties of each atomic service assure correct functionality of the entire application, nonfunctional properties such as availability, reliability, or security might significantly influence the user-perceived quality of the application. In this paper, we present CLUS, a model for reliability prediction of atomic web services that improves state-of-the-art approaches used in modern recommendation systems. CLUS predicts the reliability for the ongoing service invocation using the data collected from previous invocations. We improve the accuracy of the current state-of-the-art prediction models by considering user-, service- and environment-specific parameters of the invocation context. To address the computational performance related to scalability issues, we aggregate the available previous invocation data using K-means clustering algorithm. We evaluated our model by conducting experiments on services deployed in different regions of the Amazon cloud. The evaluation results suggest that our model improves both performance and accuracy of the prediction when compared to the current state-of-the-art models.

Prediction of Atomic Web Services Reliability for QoS-Aware Recommendation

While constructing QoS-aware composite work-flows based on service oriented systems, it is necessary to assess nonfunctional properties of potential service selection candidates. In this paper, we present CLUS, a model for reliability prediction of atomic web services that estimates the reliability for an ongoing service invocation based on the data assembled from previous invocations. With the aim to improve the accuracy of the current state-of-the-art prediction models, we incorporate user-service-, and environment-specific parameters of the invocation context. To reduce the scalability issues present in the state-of-the-art approaches, we aggregate the past invocation data using K-means clustering algorithm. In order to evaluate different quality aspects of our model, we conducted experiments on services deployed in different regions of the Amazon cloud. The evaluation results confirm that our model produces more scalable and accurate predictions when compared to the current state-of-the-art approaches.

Distributed system for lawful interception in VoIP networks

Voice over IP is one of the most propulsive technologies today. Significant advantages of VoIP over conventional telephone system provide a major incentive for enterprises and service providers to use the new technology. There is a variety of IP telephony standards, which provide basic models for implementation of VoIP. However, some significant problems still need to be adequately solved. Security, global administration and billing, emergency dialing plans and lawful interception are some of the areas that are being researched. This paper proposes a distributed system for the lawful interception in IP telephony networks. The proposed system has scalable architecture, supports various interception methods, and can be deployed on various network infrastructures. In addition, the system design addresses various issues present in IP networks, for instance; security protocols, network configuration, and standardized data formats. A prototype of the interception system, based on the proposed architecture, has been implemented and tested.

Analytical prediction of performance for cache coherence protocols

In this paper, we introduce new analytical models for predicting the performance of parallel applications under various cache coherence protocol assumptions. The purpose of these models is to determine which protocols are to be used for which data blocks, and, in the case of dynamic protocols, also to determine when to change protocols. Although we focus on tightly-coupled multiprocessor systems, similar models can be derived for loosely-coupled distributed systems, such as networks of workstations. Our models are unique in that they lie between a large body of theoretical models that assume independence and a uniform distribution of memory accesses across processors, and a large body of address-trace oriented models that assume the availability of a precise characterization of interleaving behavior of memory accesses. The former are not very realistic, and the latter are not suitable for compile-time and run-time usage. In contrast, our models enable us to choose different input parameters depending on how the models will be used and depending on the needed accuracy in performance prediction. We present the models and show how the required parameters can be obtained. We assess the accuracy of our models on 15 parallel applications. For these applications, our most complete model predicts performance within a 10 percent margin when compared to a simulation of a sequentially consistent multiprocessor system. As part of this study, we also show the potential advantage of using dynamic hybrid protocols.

Formal definition of SIP end systems behavior

The rapid improvement of hardware performance and the constantly growing bandwidth of computers have encouraged the development of communications based on computer networks. The first step in this direction is the definition of a set of protocols that will enable the design and implementation of various multimedia communication services. SIP (session initiation protocol) is a protocol for initiating multimedia conferences, and is a proposed standard, but its behavior is still not formally defined. We give a formal definition of the behavior of SIP end systems in the form of automata that include all features currently supported by SIP. The automata are defined using UML. This greatly simplifies the implementation of SIP systems compatibility between different systems based on SIP, because there are software tools that can translate UML specifications directly into the high-level languages (e.g., C++, Java).

Methods for lawful interception in IP telephony networks based on H.323

Emergence of IP telephony applications in recent years has opened numerous technical and legal problems. A particular problem in implementing IP telephony services is complying with legal requirements imposed on telephony service providers in many countries. Certain legal requirements are easy to fulfill in the conventional public circuit-switched telephone network, but present significant problems in IP telephony. One of these requirements is the possibility of electronic surveillance by authorized law enforcement agencies, i.e. wiretap service. Currently, there is no standard solution for call interception in IP telephony networks. We describe four proposed basic methods for implementing a call interception system in IP telephony networks based on the ITU-T H.323 standard. The proposed methods are Wiretap on Gateways, Wiretap Routing on the Gatekeeper, Fixed Route Wiretap, and Promiscuous Wiretap. We examine each of these four methods and show their basic advantages and disadvantages.

A Reliability Improvement Method for SOA-Based Applications

As SOA gains more traction through various implementations, building reliable service compositions remains one of the principal research concerns. Widely researched reliability assurance methods, often rely on applying redundancy or complex optimization strategies that can make them less applicable when it comes to designing service compositions on a larger scale. To address this issue, we propose a design time reliability improvement method that enables selective service composition improvements by focusing on the most reliability-critical workflow components, named weak points. With the aim of detecting most significant weak points, we introduce a method based on a suite of recommendation algorithms that leverage a belief network reliability model. The method is made scalable by using heuristic algorithms that achieve better computational performance at the cost of recommendation accuracy. Although less accurate heuristic algorithms on average require more improvement steps, they can achieve better overall performance in cases when the additional step-wise overhead of applying improvements is low. We confirm the soundness of the proposed solution by performing experiments on data sets of randomly generated service compositions.

Performance of distributed systems based on Ethernet and personal computers

In recent years, many real-time applications have emerged on the Internet. Among other types of networks, the Internet also contains a large number of local area networks (LANs) that are based on personal computers and Ethernet. Real-time systems designed for the Internet must consider the impact of this technology. The designers of these systems have a number of computer and network configuration options available and are faced with the problem of choosing the appropriate one. Since it is difficult to find performance results that cover real-time requirements for Ethernet-based personal computer systems, we have developed simple measurement software to obtain performance data. We present the measurements obtained and discuss how the data transmission speed is affected by different components of a distributed system. We show that if the appropriate components are chosen, it is possible to build a distributed system, based on Ethernet and personal computers, that has a high data transmission speed and that can efficiently use Ethernet bandwidth.