Mladen Kos

The application of Steiner trees to delay constrained multicast routing: a tabu search approach

With todays development of information technology comes the increased development of numerous real-time multimedia network applications. Some examples include video and teleconferencing, telemedicine, video-on-demand, distance education, applications in finance, etc. Several of these applications require multicasting with a certain quality of service (QoS). One of the most important QoS parameters is the maximum end-to-end delay from the source to any destination in a multicast session. This paper deals with the problem of delay-constrained multicast routing (DCMR). The DCMR problem can be reduced to the constrained minimum Steiner tree problem in graphs (CMStTG). Since the minimum Steiner tree problem in graphs (MStTG) has been proven to be NP-complete, several heuristics have been developed for solving MStTG and CMStTG. In this paper, we suggest a tabu search heuristic for the DCMR problem. This heuristic was developed on the basis of a tabu search heuristic designed for solving unconstrained minimum Steiner tree problems. Preliminary testing on data from a publicly available library, SteinLib, has shown that this heuristic gives near optimal solutions in moderate time and a moderate number of iterations for medium sized problems (50-100 nodes). Comparing with a well known algorithm for solving the CMStTG problem, tests have shown that our tabu search heuristic is superior in quality for medium sized problems.

A GRASP heuristic for the delay-constrained multicast routing problem

The increasing development of real-time multimedia network applications, many of which require multiple participants, has created the need for efficient multicast routing algorithms. Examples of such applications include video and tele-conferencing, video-on-demand, tele-medicine, distance education, etc. Several of them require multicasting with a certain Quality of Service (QoS) with respect to elements such as delay or bandwidth. This paper deals with Delay-Constrained Multicast Routing (DCMR) where the maximum end-to-end delay in a multicast session is bounded. The DCMR problem can be reduced to the Constrained Minimum Steiner Tree Problem in Graphs (CMStTG) which has been proven to be NP-complete. As a result, several heuristics have been developed to help solve it. In this paper, we developed a GRASP heuristic for the DCMR problem. Computational experiments on medium sized problems (50-100 nodes) from literature and comparison with existing algorithms have shown that the suggested GRASP heuristic is superior in quality for this set of problems.

Collaboration between academia and industry: telecommunications and informatics at the University of Zagreb

The paper deals with a model of collaboration between academia and industry in the area of information and communication technology. It shows the collaboration in the field of Telecommunications and Informatics at the University of Zagreb. Joint laboratories, the laboratory network open for experiments and demonstrations, as well as the research programme are described.

Secure target detection and tracking in mission critical wireless sensor networks

Target tracking is one of the important applications for wireless sensor networks (WSNs) that are deployed into a remote and hostile environment. In such environments, sensor nodes may be compromised by intruders to distort the integrity of data by sending false data reports, injecting false data during target tracking, and disrupting transmission of sensed data. For mission critical WSNs, such as border protection systems, the result of above attacks may be catastrophic. In this paper, we propose a secure and reliable target tracking protocol that considers security and target tracking tasks simultaneously. The basic idea behind the proposed protocol is to ensure tracking security using trust concept for individual sensor nodes. The performance evaluation results show that the use of proposed protocol allows the network to retain the trustworthiness of data even in the presence of compromised nodes thereby achieving secure and reliable target tracking process.

Static routing and wavelength assignment in wavelength routed WDM networks

In wavelength routed WDM optical networks, all-optical connections, called lightpaths, are established between pairs of nodes. Demands to set us lightpaths can be static, dynamic or scheduled. This paper deals with the problem of routing and wavelength assignment (RWA) of static lightpath demands which means that the set of demands is known a priori. This NP-complete problem has been widely studied in literature and several heuristic algorithms have been proposed. The most common objective is to minimize the number of wavelengths used. Suggested is a simple and fast algorithm for the RWA problem motivated by an efficient existing algorithm for the same problem. Testing on a series of random networks indicates that these modifications yield solutions superior in quality to those obtained by the previously suggested algorithm

A heuristic approach for path provisioning in Diff-Serv networks

To achieve QoS guarantees for predicted traffic with N quality levels in differentiated services (Diff-Serv) networks with M interior routers, an efficient heuristic algorithm for end-to-end congestion control is being developed. It can be applied as an effective tool for traffic engineering (TE) in MPLS-based networks or it can be used for network dimensioning in optimal sizing of transmission trunks, minimizing the total expansion cost. The heuristic algorithm is compared with an algorithm based on an exact approach. In all numerical test-examples the best possible result is achieved. It is obvious that heuristic option is very effective and for all cases it is possible to find the best result but with significant savings. It means that such a heuristic approach can be successfully applied for MPLS-based traffic engineering in Diff-Serv networks.

Predictive playout delay adaptation for Voice over Internet

Packet switching is an effective technology for integrating voice and data in a single network. An example for such a kind of a network is Internet. New service is emerging, and it is a Voice over Internet Protocol (VoIP). An important aspect of packet-switched voice is the reconstruction of a continuous stream of speech from the set of packets that arrive at the destination DTE (data terminal equipment). Because of the statistical nature of packet switching, each packet can encounter a different amount of delay in traversing a packet network. The problem described in this paper is how to design an appropriate voice reconstruction strategy that reproduces acceptable-quality speech from packets that arrive with varying delay. The basic idea proposed is to measure a delay jitter between several points on the Internet. Our voice traffic generator, implemented on a workstation, sends packets that are 20 ms long. The receiver measures the inter-arrival time and keeps track of mixed sequences and lost packets. The measurement results are given in a form of average delay jitter. The receiver also keeps a record of all relevant packet information in a text file that is used as an input to a delay jitter predictor. A traffic prediction element predicts talk-spurt characteristics and directly influeuces playout delay. For the prediction element, we propose an adaptive neuro-fuzzy inference system (ANFIS).

Rapid synchronization of RTP multicast sessions

Quality of Service (QoS) is an important, and admittedly overloaded, concept for emerging services based on the Real-Time Transport Protocol (RTP) to deliver multimedia content. In the context of the Internet Protocol Television (IPTV) services, the synchronization of multimedia components plays an important role. In order to synchronize audio and video components of multimedia content, RTP timestamps have to be related. Periodic Real-Time Transport Control Protocol (RTCP) Sender Report (SR) packets, which associate the RTP timestamps in the stream with a common clock at the transmitter, are associated with each stream. Thus, the frequency and the timing of the RTCP SR packets often contribute to the delay before audio and video are rendered, not just to their synchronization, because many clients will not render anything before the synchronization has been established. This paper elaborates on the different concepts for isolation of the RTCP SR packets from the RTP data flow in order to ensure the synchronization delay of the multicast multimedia sessions sufficient for lip-synchronization without excessive delay regardless of network congestion.

Priority transmission of SIP signaling flows over IP network

Signaling flow transmission is of the most importance in the discussion of the Quality of Service (QoS) problem of the Next Generation Network (NGN). For implementing service reachability, the signaling flow of the NGN services should be transmitted reliably and with the highest priority. Because the signaling flows and the media flows of the NGN service are mixed while being transmitted, the present packet-switched networks are unable to guarantee the priority and reliable transmission of signaling flows in any case of resource occupation rate. That makes it difficult to guarantee the service request triggers the framework of dynamic QoS negotiation, which performs an admission control for media flow. This paper presents the idea of priority and reliable transmission of signaling flows in packet-switched networks. The following simulation study is an effort to determine the possibility of Internet Protocol (IP) network to provide priority and reliable transmission of Session Initiation Protocol (SIP) signaling flows and identify opportunities for improvement, and development of a new method to ensure priority, as well as reliable transmission of signaling flows.

Priority Transmission of SIP Signaling Flows in Case of IP Link Congestion

Conceptual framework of Next Generation Network (NGN) is based on Internet Protocol (IP) transport technology, which is generally accepted as the optimal solution for delivering of next generation multimedia services. Although packet-switched networks are in the mainstream, decades of experience with circuit-switched networks still set expectations when it comes to Quality of Service (QoS). As opposed to circuit-switched networks, signaling flow and media flow of NGN services are mixed in transmission. That makes it difficult for an IP network node to guarantee the signaling flow packet is not discarded in case of the congestion, which results in an impossibility to trigger the framework of dynamic QoS negotiation and implement service reachability. Since the service reachability is guaranteed in the signaling flow transmission aspect, it is necessary to consider the possibility of IP network to fulfill expectations regarding the straightway and reliable transmission of signaling flows. In this paper, the link congestion effect on critical performance metrics of Session Initiation Protocol (SIP) signaling flows is investigated by performing extensive simulation study. Our results indicate that IP network is able to guarantee transmission criteria of SIP signaling flows even in case of critical link congestion when the highest priority is assigned to them.