We consider the offline version of the impairment-aware routing and wavelength assignment (IA-RWA) problem in transparent all-optical networks as a cross layer optimization problem. In optical networks and in the abse...
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We consider the offline version of the impairment-aware routing and wavelength assignment (IA-RWA) problem in transparent all-optical networks as a cross layer optimization problem. In optical networks and in the absence of regenerators, optical signal quality degrades due to physical layer impairments. We initially present an algorithm for solving the RWA problem based on an LP relaxation formulation that has acceptable integrality performance. To account for signal degradation due to physical layer impairments we extend our RWA formulation and constrain the interference among lightpaths using noise variance related parameters. The objective of the resulting optimization problem is not only to serve the connection requests by minimizing the number of utilized wavelengths, but also to select lightpaths that have acceptable physical layer performance.
This paper presents the performance evaluation of a multi-rate multicast protocol named adaptive smooth simulcast protocol (ASSP) for simulcast video transmission. ASSP implements a single rate TCP-friendly protocol a...
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This paper presents the performance evaluation of a multi-rate multicast protocol named adaptive smooth simulcast protocol (ASSP) for simulcast video transmission. ASSP implements a single rate TCP-friendly protocol as the underlying congestion control mechanism for each simulcast stream. ASSP is built on top of the RTP/RTCP protocol and exploits the RTCP sender and receiver reports for the dissemination of feedback information. The key attributes of ASSP are: a) TCP-friendly behavior, b) adaptive per-stream transmission rates, c) adaptive scalability to large sets of receivers and finally d) smooth transmission rates that are suitable for multimedia applications. We evaluate the performance of ASSP under an integrated simulation environment, which extends ns-2 and Evalvid-ra into the multicast domain with the use of RTP/RTCP protocols. Simulations conducted under this environment combine the measurements of network metrics along with objective evaluation criteria on the perceived video quality by the end user.
In this paper we study load balancing in a cluster based p2p system. The cluster based architecture is chosen after the study of various real systems. We then define the notion of load for that system and describe coe...
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In this paper we study load balancing in a cluster based p2p system. The cluster based architecture is chosen after the study of various real systems. We then define the notion of load for that system and describe coefficients that measure the different parameters of load. We use these coefficients to define load factors that can be used to measure each node's load. These factors are also used in two algorithms that balance the load fairly among all peers in a cluster. We improve the algorithms' balancing performance using replication of popular objects. A set of metrics is used to evaluate the cost of each algorithm and the effect on system's performance. Our simulation results show that it is possible to improve the fairness on load distribution without replication but with a small reduce on system's throughput. And under the cost of replicating a small amount of objects we improve fairness without reducing system's throughput.
The voting rules proposed by Dodgson and Young are both designed to find the alternative closest to being a Condorcet winner, according to two different notions of proximity; the score of a given alternative is known ...
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The voting rules proposed by Dodgson and Young are both designed to find the alternative closest to being a Condorcet winner, according to two different notions of proximity; the score of a given alternative is known to be hard to compute under either rule. In this paper, we put forward two algorithms for approximating the Dodgson score: an LP-based randomized rounding algorithm and a deterministic greedy algorithm, both of which yield an O(logm) approximation ratio, where m is the number of alternatives; we observe that this result is asymptotically optimal, and further prove that our greedy algorithm is optimal up to a factor of 2, unless problems in NP have quasi-polynomial time algorithms. Although the greedy algorithm is computationally superior, we argue that the randomized rounding algorithm has an advantage from a social choice point of view. Further, we demonstrate that computing any reasonable approximation of the ranking produced by Dodgson's rule is NP-hard. This result provides a complexity-theoretic explanation of sharp discrepancies that have been observed in the Social Choice Theory literature when comparing Dodgson elections with simpler voting rules. Finally, we show that the problem of calculating the Young score is NP-hard to approximate by any factor. This leads to an inapproximability result for the Young ranking.
We design and implement a multicost impairment- aware routing and wavelength assignment algorithm for online traffic. In transparent optical networks the quality of a transmission degrades due to physical layer impair...
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We design and implement a multicost impairment- aware routing and wavelength assignment algorithm for online traffic. In transparent optical networks the quality of a transmission degrades due to physical layer impairments. To serve a connection, the proposed algorithm finds a path and a free wavelength (a lightpath) that has acceptable signal quality performance by estimating a quality of transmission measure, called the Q factor. We take into account channel utilization in the network, which changes as new connections are established or released, in order to calculate the noise variances that correspond to physical impairments on the links. These, along with the time invariant eye impairment penalties of all candidate network paths, form the inputs to the algorithm. The multicost algorithm finds a set of so called non-dominated Q paths from the given source to the given destination. Various objective functions are then evaluated in order to choose the optimal lightpath to serve the connection. The proposed algorithm combines the strength of multicost optimization with low execution time, making it appropriate for serving online connections.
In future transparent optical networks, it is important to consider the impact of physical impairments in the routing and wavelengths assignment process, to achieve efficient connection provisioning. In this paper, we...
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In future transparent optical networks, it is important to consider the impact of physical impairments in the routing and wavelengths assignment process, to achieve efficient connection provisioning. In this paper, we use classical multi-objective optimization (MOO) strategies and particularly genetic algorithms to jointly solve the impairment aware RWA (IA-RWA) problem. Fiber impairments are indirectly considered through the insertion of the path length and the number of common hops in the optimization process. It is shown that blocking is greatly improved, while the obtained solutions truly converge towards the Pareto front that constitutes the set of global optimum solutions. We have evaluated our findings, using an Q estimator tool, that calculates the signal quality of each path analytically.
Multi-rate multicast schemes can be broadly classified into two categories. In layered multicast, a video file is transmitted by a base layer, which contains the most important features of the video. Additional layers...
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ISBN:
(纸本)9781424449736
Multi-rate multicast schemes can be broadly classified into two categories. In layered multicast, a video file is transmitted by a base layer, which contains the most important features of the video. Additional layers, called enhancement layers, contain data that refine the quality of the base layer. In simulcast, the video file is transmitted by replicated layers that contain the same content at different quality. The benefits of layered multicast versus simulcast are still under question, as layered multicast presents higher complexity and more challenging deployment than simulcast. In this paper, two multi-rate multicast control schemes are compared. The layered multicast SMCC congestion control against our proposed solution for simulcast transmission, named ASSP. We compare the two schemes under a controlled simulation environment with the network simulator software (ns-2) by taking into account the evaluation criteria in RFC 5166. The results demonstrate that both SMCC and ASSP are TCP-friendly while SMCC seems to suffers from small oscillations of the transmission rate. In network topologies with low complexity ASSP consumes no more bandwidth than SMCC for the transmission of the different simulcast streams, while being a simpler solution than the more complicated SMCC.
Multistage Interconnection Networks (MINs) provide efficient communication resources between network components in an appealing cost/performance relation. Consequently, they have been widely used on Internet connectio...
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Multistage Interconnection Networks (MINs) provide efficient communication resources between network components in an appealing cost/performance relation. Consequently, they have been widely used on Internet connections such as ATM and gigabit Ethernet switches, terabit routers as well as for interconnecting parallel systems. In this paper a novel analytical method for providing performance evaluation on MINs is presented under multicast environment. The proposed analysis was applied on various network size MINs constructed by variable buffer-length switching elements (SEs) per network stage, supporting mixed traffic patterns such as unicast and multicast, under various offered loads in uniform traffic conditions. The applied multicasting policy, where a packet is copied and transmitted when only both destination buffers are available has not been considered insofar by former models. This mechanism, which is called "full-multicast" was employed by all SEs using the "cell replication while routing" (CRWR) *** proposed architecture, which is thoroughly analyzed by our novel analytical model, can be also useful in performance study and development of other Internet communication links supporting multicast traffic.
The aim of the Code4Thought project was to deliver a tool supported methodology that would facilitate the evaluation of a software product's quality according toISO/IEC-9126 software engineering quality standard. ...
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The aim of the Code4Thought project was to deliver a tool supported methodology that would facilitate the evaluation of a software product's quality according toISO/IEC-9126 software engineering quality standard. It was a joint collaboration between Dynacomp S.A. and the Laboratory for Graphics, Multimedia and GIS of the department of computerengineering and informatics of the University of Patras. The Code4thought project focused its research on extending the ISO/IEC-9126standard by employing additional metrics and developing new methods for facilitating system evaluators to define their own set of evaluation attributes. Furthermore, to develop innovative and platform-free methods for the extraction of elements and metrics from source code ***, to design and implement new data mining algorithms tailored for the analysis of software engineering data.
We present in this paper a simulation-based comparison of one of the best known multicast congestion control schemes - TFMCC - against our proposed adaptive smooth multicast protocol (ASMP). ASMP consists of a single-...
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We present in this paper a simulation-based comparison of one of the best known multicast congestion control schemes - TFMCC - against our proposed adaptive smooth multicast protocol (ASMP). ASMP consists of a single-rate multicast congestion control, which takes advantage of the RTCP sender (SR) and receiver reports (RR) in order to adjust the sender's transmission rate in respect of the network conditions. The innovation in ASMP lays in the "smooth" transmission rate, which is TCP-friendly and prevent oscillations. We use an integrated simulation environment named Multi-Evalvid-ra for the evaluation of the two congestion control schemes. Multi-Evalvid-ra provides all the necessary tools to perform simulation studies and assess the video quality by using both network related metrics along with video quality measurements. The performance evaluation results show that ASMP is a very efficient solution for rate adaptive multimedia applications and a serious competitor to well know TFMCC.
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