Available bandwidth-based real-time multicast routing distributed algorithm

Given a network with one source and multiple destinations, the multicast delay variation problem attempts to construct a multicast tree such that the interdestination delay variation among all the paths from the source to each destination is minimized. In this paper, we show that the problem is NP-hard and that it is not approximable within a constant factor in polynomial time unless NP = P. These findings indicate that it is impossible to develop efficient optimal or approximation algorithms for any multicast routing problem under the interdestination delay variation constraint unless NP = P.

Multicast routing for real-time applications has two important requirements: minimal network cost and shortest network delay. It is always difficult to meet one requirement without compromising the other. This paper presents a real-time multicast routing algorithm which minimizes overall network cost without letting the delay from source to any destination exceed a time constraint. The multicast routing with optimal overall network cost is an NP-complete problem. Our algorithm is based on the idea of the minimum spanning tree heuristic.

Quality of service (QoS) provisioning generally assumes more than one QoS measure which implies that QoS routing can be categorized as an instance of routing subject to multiple constraints: delay-jitter, bandwidth, cost, etc. We study the problem of constructing multicast trees to meet the QoS requirements of real-time interactive applications where it is necessary to provide bounded delays and bounded delay variation among the source and all destinations while keeping overall cost of the multicast tree low. The main contribution of our work is a new strategy for constructing multiconstrained multicast trees. We first derive mathematically a new Delay-Variation Estimation Scheme and prove its efficiency. Thereafter, we propose a simple and competitive (in terms of system running time) heuristic algorithm, for delay and delay variation constrained routing problem based on the proposed delay-variation estimation scheme and using the Extended Prim-Dijkstra tradeoffs' algorithm. Besides, our algorithm uses cost information only from neighboring nodes as it proceeds which makes it more practical from an implementation point of view. Our contribution also extends previous works in providing some properties and analyses of delay bounded paths satisfying delay variation constraints.

Real-time applications such as VoIP, video-conference or online games are delay-sensitive multimedia applications and require relatively small delay and small delay variation. Recently, IEEE 802.11 WLANs have reached an important stage and have become a common technology for wireless access due to its low cost, ease of deployment and mobility support. Its new standard, EDCA, has the ability to accommodate real-time traffic and provide relatively small delay. However, it cannot achieve small delay variation due to the burst feature of its backoff mechanism after a collision or a frame error. Since the real-time services such as Voice over IP (VoIP) has a delay constraint to guarantee a QoS, a fast retransmission scheme for corrupted frames is required. In this paper, we propose a new fast retransmission mechanism for VoIP frames to reduce the delay and delay variation. Then, we integrate our scheme with an Adaptive Jitter Buffer (AJB) algorithm to optimize end-to-end QoS performance. Simulation results indicate that proposed fast retransmission scheme reduces not only delay, delay variation and dropping probability of frames, but it also helps the AJB to support QoS maintaining voice quality at high level on EDCA-based WLANs.

In the design of power-aware on-demand routing protocols in mobile ad hoc networks, it must be taken into account that nodes may use a great amount of power to find the desired routing path during the path-discovery phase. In addition, in previous research on power-aware routing protocols, the path bandwidth was often not considered. In this paper, we tackle these issues by proposing a power-aware routing protocol with low route requests (LRR) to find a path with high path bandwidth. By making a low number of routing requests (RREQs), mobile nodes help to broadcast the routing request only when they first receive the routing requests. In addition, based on the receipt of the routing requests from the neighboring nodes, mobile nodes record the location information of its one-hop neighboring nodes. In the path-reply phase, mobile nodes in the found path use the collected location information of their neighbors and our proposed relay model to modify the found path so that the found path has high bandwidth. In our simulation, we compared our proposed routing protocol (LRR) with ad hoc on-demand distance vector, dynamic source routing and min–max battery capacity routing in terms of the following: power consumption in the path-discovery phase and the path-reply phase, bandwidth of the found path, power consumed during data transmission and overall power consumption. In addition, we compared our two proposed routing protocols, the minimum power consumption routing protocol that selects one path with minimum transmission power from all paths and the LRR routing protocol, in terms of the following: the power consumption in the path-discovery phase, the path bandwidth and the overall power consumption. From the simulation results and the analysis, we can see that the proposed LRR routing protocol that uses a low number of routing requests and our proposed relay model to improve path bandwidth can efficiently reduce the overall power consumption.

We propose two new algorithms called BiLAD and ExactBiLAD for the well-known Single-Constrained Shortest Path (SCSP) problem. It is a fundamental problem in quality-of-service (QoS) routing, where one seeks a source-destination path with the least cost satisfying a delay QoS constraint in a network. As pointed out by Juttner et al. , there is no widely accepted algorithm with polynomial time to the SCSP problem because the SCSP problem is NP-hard. The remarkable feature of BiLAD is that it ensures that the length of iteratively updated angle interval is shrunk at least at a constant ratio. With the help of this feature, we prove its polynomial time complexity. To the best of our knowledge, this is the first time that the polynomial time complexity is proved in details. The numerical results show that, in most QoS routing test instances, the performance of BiLAD is close to their primal optimal solutions. The proposed modified Dijkstra procedure, whose complexity is the same as that of the Dijkstra algorithm, also accelerates BiLAD. In the second part of the paper, based on the information obtained by BiLAD, we design an exact algorithm–ExactBiLAD, in which an optimal solution to the SCSP problem is finally obtained by scanning the steadily reduced optimal-path-candidate triangle area. The simulation results indicate that ExactBiLAD needs only a dozen times of executing the modified Dijkstra algorithm regardless of the network size or the average node degree. Distinguished from many other exact algorithms, ExactBiLAD has a satisfactory performance in the practical computation.

In this paper, a novel modeling framework is proposed to quickly estimate the delay variability of logic paths due to random variations, and evaluate the related design margin. The analysis shows that the popular fan-out-of-4 metric F04 can capture the impact of technology and voltage on the delay variations of logic paths. Once those contributions are isolated, the impact of random variations on standard cells' delay is accounted for by means of cell-specific coefficients that are evaluated in a preliminary library characterization phase. The proposed framework is very general and applicable from sub-threshold to nominal voltage, and provides the designer with a deep insight into the main delay variability contributions in a path. It also predicts the impact of design modifications (e.g., logic restructuring, cell up-sizing), and is well suited for pencil-and-paper calculations. Case studies involving three critical paths extracted from designs ranging from microprocessors to specialized hardware show adequate accuracy, with a delay variability error being typically less than 10%.

Designing soft-edge flip-flop-based linear pipelines operating in multiple supply voltage regimes

Spaceborne interferometric synthetic aperture radar (SAR) (InSAR) imaging has been used for over a decade to monitor tectonic movements and landslides, as well as to improve digital elevation models. However, InSAR is affected by variations in round-trip propagation delay due to changes in ionospheric total electron content and in tropospheric humidity and temperature along the signal path. One of the largest sources of uncertainty in estimates of tropospheric path delay is the spatial and temporal variability of water vapor density, which currently limits the quality of InSAR products. This problem can be partially addressed by using a number of SAR interferograms from subsequent satellite overpasses to reduce the degradation in the images or by analyzing a long time series of interferometric phases from permanent scatterers. However, if there is a sudden deformation of the Earth's surface, the detection of which is one of the principal objectives of InSAR measurements over land, the effect of water vapor variations cannot be removed, reducing the quality of the interferometric products. In those cases, high-resolution information on the atmospheric water vapor content and its variation with time can be crucial to mitigate the effect of wet-tropospheric path delay variations. This paper describes the use of a ground-based microwave radiometer network to retrieve 3-D water vapor density with fine spatial and temporal resolution, which can be used to reduce InSAR ambiguities due to changes in wet-tropospheric path delay. Retrieval results and comparisons between the integrated water vapor measured by the radiometer network and satellite data are presented.

This paper describes the path selection function in Networking BroadBand Services (NBBS), which is IBM's architecture for high-speed, multimedia networks. The distinguishing feature of a multimedia network is its ability to integrate different applications with different traffic characteristics and service requirements in the network, such as voice, video, and data. In order to meet their service requirements, it is necessary for the network to provide unique quality-of-service (QOS) guarantees to each application. QOS guarantees, specified as multiple end-to-end performance objectives, translate into path and link constraints in the shortest path routing problem. For a general cost function, shortest path routing subject to path constraints is known to be a nonpolynomial- (NP-) complete problem. The NBBS path selection algorithm, a heuristic solution based on the Bellman-Ford algorithm, has a polynomial order of complexity. The algorithm finds a minimum hop path satisfying an end-to-end delay (or delay variation) constraint, that in most cases also optimizes a load balancing function. To reduce the number of path constraints, other QOS requirements such as packet loss ratio are implemented as a link constraint. The notion of primary and secondary links is used to minimize the long-term overall call blocking probability by dynamically limiting the hop count of a given path. The path selection algorithm developed for point-to-point connections is described first, followed by its extension to the case of point-to-multipoint connections.

The winner determination problem (WDP) for a single object auction is a relatively easy problem to solve using the greedy algorithm. It can be formulated and solved using the MIP optimization solver. In this thesis, we applied WDP to solve a booth auction which is one of the nonidentical multiple-object auctions known to be NP-hard. Formulation of the winner determination model for a linear arrangement of a multiple-object auction is explained in this study. Moreover, this research improves the algorithm from the study of Rothkopf et al (1998) having polynomial time complexity. Finally, the comparison of a running time exhibits the advantage of our proposed algorithm. The simulation results are discussed.

Mobile ad hoc networks (MANETs) consist of a set of nodes which can move freely and communicate with each other wirelessly. Due to the movement of nodes and unlike wired networks, the available routes used among the nodes for transmitting data packets are not stable. Hence, proposing real-time routing protocols for MANETs is regarded as one of the major challenges in this research domain. Algorithms compatible with the changes created in the network due to the nodes' movements are of high significance. For reducing data packet transmission time among nodes, not only should route shortness be considered but also route stability should be taken into consideration. Since available factors in different environments have specific behavior patterns especially in human environments, the parameters of link stability and route shortness were taken into consideration and the reinforcement learning was used to propose a method so as to make the best choice among the neighbors at any moment to transmit a packet to the destination. That is, the proposed method was aimed at predicting the behavior pattern of the nodes in relation to the target node through using reinforcement learning. The proposed method used Q-learning algorithm which has more homogeneity to estimate the value of actions. Simulation results in OPNET demonstrate the superiority of the proposed scheme over conventional MANET routing methods.

A delay-constrained and priority-aware channel assignment algorithm for efficient multicast in wireless mesh networks

Multi point routing algorithms capable of satisfying quality of service constraints such as delay boundedness and delay variation boundedness are becoming crucial with the advent of high speed networks. This paper addresses the problem of determining minimum cost paths to nodes in a multicast group satisfying delay bounds and delay variation bounds. A routing protocol is proposed and compared with previous schemes like DVMA (delay variation bounded multicast algorithm). The results show that the scheme proposed improves over the DVMA in the variation bounds achieved and is comparatively far more efficient.

This paper presents the simulation and experimental analysis of an impulse voltage generator (IVG) used for atmospheric discharge voltage tests. The electrical equivalent circuit of the IVG was simulated using the electromagnetic transients program EMTP-VR. Besides the simulation of the generator operation, it was necessary to make a detailed revision of the IVG components and determine their working condition to carry the laboratory experiments. The lack of a high DC voltage source to feed the IVG led to developing a high-voltage dc supply. Although the IVG was designed and built in February 1982, this equipment was out of operation due to its DC power supply failure. Due to the interest in rehabilitating the equipment to perform high voltage experiments, and with the need to characterize insulation materials and electrical equipment subject to electrical stress, it was decided to put it back into operation. Capacitor tests were carried out for each IVG stage to determine if they fulfilled the electrical charging function. Other components were also repaired, such as damaged resistances and sphere gaps. The impulse generator was configured with a maximum of six stages which is half of the original design. Before doing an experiment with the IVG, a simulation analysis was made to study the IVG. The simulation results allow evaluating before the experimentation whether the impulse generator is working correctly; the model allows to analyze the charge and discharge of each capacitor and the electrical currents at each branch of the IVG equivalent circuit. Performance Simulation and experimental results are presented to demonstrate the IVG functionality. The IVG will be used for carrying out insulation tests made by power engineering graduate students.