Efficient collective communication in WDM networks with a power budget

A scheme for enhancing sensor network lifetime is proposed using multiple mobile CHs. The CHs controllably move toward the energy-rich sensors maintaining remaining energy more evenly, eliminating multihop transmission. Collaboration among CHs is considered to maintain their continuous connectivity to the base station (BS) to reduce the delay in communication. Network lifetime is increased by 75% by making CHs always move towards a stable equilibrium point whereas connectivity algorithm provides 40% improvement in transmission delays over existing schemes.

Studies issues of multicasting in multistage interconnection networks (MINs) for large-scale multicomputers. In addition to point-to-point communication among the processing nodes, efficient collective communication is critical to the performance of multicomputers. This paper presents a new approach to support multicast communication, on the basis of a restricted address encoding scheme which constructs a short fixed-size multicast header, and a recursive scheme that recycles a multicast packet one or more times through the network to send it to the desire destination nodes. We propose a novel deadlock-free multicast algorithm for multiple multicast packets in MIN-based multicomputers. We also present a performance model for the unbuffered MIN using the multicast algorithm and analyze its performance in terms of the network throughput, where several multicast communications are considered.

This thesis focuses on exploring a multicast communication protocol forWiFi Direct (WD) 802.11 networks. The aim is to improve reliability and efficiency of multicast communication in WD networks. Multicast inWDhas numerous potential applications such as local content sharing, sharing network services, playing multi-player games, and a number of other proximity based services in various fields, viz. health, sports, agriculture, transportation, and gaming. The two major issues with multicast, reliability and efficiency, have been extensively studied in literature for standard WiFi 802.11 networks. However, multicast protocols used in standard WiFi 802.11 networks cannot be straightforwardly used in WD networks because the two technologies are different. Some of these differences include multicast group formation, group architecture, network topology, role and capacity of multicast transmitter. As a result, a multicast protocol cannot achieve reliability and efficiency without taking into account the specifications of the MAC and PHY layers of WD 802.11 networks. Motivated from the leader based approaches of standard WiFi, an Enhanced Leader Based Multicast (ELBM) protocol is proposed to achieve reliability in multicast communication in WD networks. It reduces collision and interference in multicast data transmission by improving the channel access mechanism and selecting an optimal representative multicast receiver. In order to assess the performance improvement which results from early detection of packet collision, Early Packet Loss Detection (EPLD) analytical model is proposed, which surpasses the standard protocol in terms of system throughput. Similarly, a theoretical model is formulated to investigate the new features of the MAC and PHY layers of 802.11ac, such as different Multiple In Multiple Out (MIMO) configurations, Modulation and Coding Schemes (MCS), and wider channel bandwidths under TGn channel models. Because hidden nodes can largely affect the throughput of WD networks, therefore an improved analytical model known as Vidden is developed to analyse the Very High Throughput (VHT) of 802.11ac in the presence of hidden stations. Vidden carefully calculates the collision probability by taking into account both the contending, as well as, the hidden stations A novel adaptive algorithm is proposed to maximize the efficiency of WD 802.11 networks under a TGn channel model by choosing optimal PHY parameters in accordance with targeted Quality of Experience (QoE) for a particular application. The simulation results show that the proposed method outperforms the standard method, thereby achieving an optimal performance in an adaptive manner. Thereafter, an efficient methodology is proposed to reduce the overall Packet Error Rate (PER) based on the simulation results. Finally, the problem of selecting the most favourable transmission channel and rate is investigated for a multicast communication system in the context of WD 802.11 networks. To this end, a novel Multi-rate Multi-channel Multicast (M3-Cast) protocol is proposed, which not only chooses the most favourable communication channel and transmission rate but also takes into account the implementation details of the underlying WD technology, thereby optimizing the overall system performance. M3-Cast is formulated analytically and evaluated by a complete system level simulation. The detailed results and analysis consider a number of performance metrics, such as bit error rate (BER), multicast capacity, and system throughput under different MIMO configurations, channel bandwidths, and various network radii. Consequently, the simulation and analytical results show that M3-Cast protocol outperforms the standard multicast protocol of WD by almost two-fold in terms of system throughput.

Efficient routing of messages is a key to the performance of multicomputers. Multicast communication refers to the delivery of the same message from a source node to an arbitrary number of destination nodes. While multicast communication is highly demanded in many applications, most of the existing multicomputers do not directly support this service; rather it is indirectly supported by multiple one-to-one or broadcast communications, which result in more network traffic and a waste of system resources. In this paper, we study routing evaluation criteria for multicast communication under different switching technologies. Multicast communication in multicomputers is formulated as a graph theoretical problem. Depending on the evaluation criteria and switching technologies, we study three optimal multicast communication problems, which are equivalent to the finding of the following three subgraphs: optimal multicast path, optimal multicast cycle, and minimal Steiner tree, where the interconnection of a multicomputer defines a host graph. We will show that all these optimization problems are NP-complete for the popular 2D-mesh and hypercube host graphs. Heuristic multicast algorithms for these routing problems are proposed. © 1993 IEEE

In certain types of Internet applications, multicasting with Quality of Service (QoS) optimizations are required on both the end-to-end delay from the source to the destinations, as well as the difference in the end-to-end delay between the destinations. Examples of these applications include video-conferencing, online games, and distributed database replication. These applications require that the messages should reach all the destinations within a specified period of time and all the destinations should receive the message from the source almost at the same time. The solutions to the Delay and Delay Variation Bounded Multicast Network (DVBMN) problem involve generating a network which spans the source and the group of destinations such that the end-to-end delay from source to each destination is within a bound and the delay variation among all the destinations is minimum. The Chains heuristic proposed in the literature provides such a multicast network which achieves the tightest delay variation with minimum execution time. To test the performance of multicasting using the multicast network generated by Chains heuristic on the Internet, we have implemented a prototype of a multicast network using Chains and experimented multicasting with the prototype on PlanetLab. PlanetLab is an overlay testbed which connects more than 1000 nodes all over the world. We have analyzed the performance of multicasting using the prototype on PlanetLab. Results show that the measured value of maximum delay variation from the prototype approximately matches with the value calculated by Chains for a small number of destination nodes. However, as the number of destination nodes increases, the measured value of maximum delay variation from the prototype quickly increases.

The multiple destination routing (MDR) problem can be formulated as finding a minimal cost tree which contains designated source and multiple destination nodes so that certain constraints in a given communication network are satisfied. This is a typical NP-hard problem, and therefore only heuristic algorithms are of practical value. As a first step, a new genetic algorithm is developed to solve the MDR problems without constraints. It is based on the transformation of the underlying network of an MDR problem into its distance complete form, a natural chromosome representation of a minimal spanning tree (an individual), and a completely new computation of the fitness of individual. Compared with the known genetic algorithms and heuristic algorithms for the same problem, the proposed algorithm has several advantages. First, it guarantees convergence to an optimal solution with probability one. Second, not only are the resultant solutions all feasible, the solution quality is also much higher than that obtained by the other methods (indeed, in almost every case in our simulations, the algorithm can find the optimal solution of the problem). Third, the algorithm is of low computational complexity, and this can be decreased dramatically as the number of destination nodes in the problem increases. The simulation studies for the sparse and dense networks all demonstrate that the proposed algorithm is highly robust and very efficient in the sense of yielding high-quality solutions.

The efficient and high throughput multicast communication in interconnection networks is known as a fundamental but hard problem. In the literature, most of the related works handle multicast communication within limited operating conditions and low throughput. Recently, a new multicast scheme, known as qualified groups QG, was proposed in [2] and has shown promising performance characteristics. However, this scheme has been examined only, so far, under deterministic routing and symmetric networks. In order to examine the QG in more realistic and different scenarios, this paper makes two major contributions. Firstly, the QG is generalised here to handling multicast communication in symmetric, asymmetric and different network sizes. Secondly, unlike most existing multicast algorithms the present study proposes a new adaptive multicast algorithm that maintains good performance levels for various system sizes. Our experiments show that the QG exhibits significant improvement in both throughput and multicast latency.

This paper addresses the issue of throughput-delay of one-to-many wireless multi-hop flows based on random linear network coding (RLNC). Existing research results have been focusing on the single-hop model which is not suitable for wireless multi-hop networks. In addition, the conditions of related system model are too idealistic. To address these limitations, we herein investigate the performance of a wireless multi-hop network, focusing on the one-to-many flows. Firstly, a system model with multi-hop delay was constructed; secondly, the transmission schemes of system model were gradually improved in terms of practical conditions such as limited queue length and asynchronous forwarding way; thirdly, the mean delay and the mean throughput were quantified in terms of coding window size if and number of destination nodes N for the wireless multi-hop transmission. Our findings show a clear relationship between the multi-hop transmission performance and the network coding parameters. This study results will contribute significantly to the evaluation and the optimization of network coding method.

It is true that in all-optical networks, network performance can be improved by wavelength conversion. However, the switching node with wavelength conversion capability is still costly, and the number of such nodes should be limited in the network. In this paper, a performance optimization problem is treated in all-optical networks. We propose a heuristic algorithm to minimize an overall blocking probability by properly allocating a limited number of nodes with wavelength conversion capability. The routing strategy is also considered suitable to the case where the number of wavelength convertible nodes are limited. We validate the minimization level of our heuristic algorithm through numerical examples, and show that our algorithm can properly allocate nodes with conversion for performance optimization.

All-optical networks have been largely investigated due to their high data transmission rates. In the traditional Wavelength-Division Multiplexing (WDM) technology, the spectrum of light that can be transmitted through the optical fiber has been divided into frequency intervals of fixed width, with a gap of unused frequencies between them. Recently, an alternative emerging architecture was suggested which moves away from the rigid Dense WDM (DWDM) model towards a flexible model, where usable frequency intervals are of variable width (even within the same link). Each light path has to be assigned a frequency interval (sub-spectrum), which remains fixed through all of the links it traverses. Two different light paths using the same link must be assigned disjoint sub-spectra. This technology is termed flex-grid (or, flex-spectrum), as opposed to fixed-grid (or, fixed-spectrum) current technology. In this work we study a problem of optimal bandwidth allocation arising in the flex-grid technology. In this setting, each light path has a lower and upper bound on the width of its frequency interval, as well as an associated profit, and we want to find a bandwidth assignment that maximizes the total profit. This problem is known to be NP-Complete. We observe that, in fact, the problem is inapproximable within any constant ratio even on a path network. We further derive NP-hardness results and present approximation algorithms for several special cases of the path and ring networks, which are of practical interest. Finally, while in general our problem is hard to approximate, we show that an optimal solution can be obtained by allowing resource augmentation. Our study has applications also in real time scheduling.

The method in which Routing and Wavelength Assignment (RWA) of connection requests is performed in optical WDM networks, can appreciably affect resource consumption. The blocking probability for lightpath requests increases significantly with increase in resource consumption. Thus the method of performing RWA should be such that it minimizes consumption of network resources. RWA in all-optical networks is an NP-Complete problem. This paper proposes six new heuristic algorithms for static RWA in all-optical mesh networks that are not only efficient in terms of resource conservation but can also solve the RWA problem effectively in polynomial time. Comparisons show that the proposed algorithms perform better than some earlier well-known strategies.

Multi robot systems (MRS) have been an active research area for many years. With the robot systems leaving the laboratory environment, the aspect of wireless communication is getting more important. Especially in multi robot systems wireless communication is crucial, but existing middleware for robot systems does not regard the challenges of wireless communication. Among other aspects the fluctuation of link delay, bandwidth and availability is characteristic for wireless communication. A communication system in a multi robot system must be capable to manage these challenges. Another issue is efficient point to multipoint (multicast) communication. This allows the availability of the same data to multiple recipients without an unnecessary high increase of network load compared to unicast communication schemes.We therefore propose a multicast communication framework for a multi robot system based on wireless communication. The framework is organised in two parts. The first part is a general framework for a wireless multicast communication protocol, which is optimized to offer efficient multicast communication capabilities on wireless networks and takes the available link qualities into account. The second part is a framework for a robot middleware, which benefits from the multicast communication optimizations of the first part. The framework assumes unreliable communication, thus taking fluctuating link qualities into account. Both parts are already implemented on a real system and are used in an experimental multi robot system.

An improved approximate network blocking probability model for all-optical WDM Networks with heterogeneous link capacities

In this chapter we study the planning (offline) problem in WDM networks. In such networks, the signal quality of transmission (QoT) degrades due to physical-layer impairments, making necessary the use of regeneration at some intermediate nodes for certain lengthy lightpaths. Because of physical effects, routing choices made for one lightpath affect and are affected by the choices made for the other lightpaths. This interference among the lightpaths is particularly difficult to formulate in a planning algorithm, since in this version of the problem, we start without any established connections, and the utilization of lightpaths is the variable of the problem. We present a way to formulate inter-lightpath interference as additional constraints on the routing and wavelength assignment (RWA) problem. We initially present algorithms to solve the problem of planning a transparent all-optical WDM network, that is, a WDM network without regeneration capability. Then, we turn our attention to translucent WDM optical networks and present a series of algorithms that choose the regeneration sites and the number of regenerators required on these sites, solving the regenerator placement and the RWA problem for a given set of requested connections.

In this paper, a novel concept of multi-link failure isolation is proposed on all-optical networks (AONs). In our study, the basis of fault diagnosis, which is supported by link management protocol (LMP), is introduced for rapid deployment on GMPLS networks. Yet, the LMP is incapable to detect multi-link failure on the same light path, thus, adding the addition of probing path is an efficient strategy for solving its insufficient fault diagnostic capability. To implement this strategy and make our mechanism feasible in reality, an addition method of active probes is developed for AONs which are equipped with LMP (link management protocol) and backup path establishment. With the aids of established light paths/backup paths, engineered additional probes and LMP, our mechanism gathers much more information for fault diagnosis than any other ones do to achieve k-fault diagnostic capability. Besides, our study provides a resilient method for resetting (adjustable) k-fault diagnostic capability without recalculating the whole system. Also, the issue of cost-effective is also in our concern. The experimental results are compared with those of the m-cycle, fault inference with healthy information (FIHI), optimal and our mechanisms. The performance reveals that our proposed mechanism can reach our objective.