Deadlock-Free Multicasting in Irregular Networks Using Prefix Routing

A deadlock-free multicast scheme called prefix multicasting in irregular networks (i.e., networks with irregular topology) is studied. In prefix routing, a compact routing table is associated with each node (processor). Basically, each outgoing channel of a node is assigned a special label and an outgoing channel is selected if its label is a prefix of the label of the destination node. Node and channel labelling in an irregular network is based on a pre-defined spanning tree which may or may not be minimum. The routing process follows a two-phase process of going up and then down along the spanning tree, with a possible cross channel between two branches of the tree between two phases. It is shown that the proposed routing scheme is deadlock- and livelock-free. The approach is extended to multicasting in which the multicast packet is first forwarded up the tree to the longest common prefix (LCP) of destinations in the multicast. The packet is then treated as a multi-head worm that can split at branches of the spanning tree as the packet is sent down the tree.     

Leapfrog: Optimal Opportunistic Routing in Probabilistically Contacted Delay Tolerant Networks

Delay tolerant networks (DTNs) experience frequent and long lasting network disconnection due to various reasons such as mobility, power management, and scheduling. One primary concern in DTNs is to route messages to keep the end-to-end delivery delay as low as possible. In this paper, we study the single-copy message routing problem and propose an optimal opportunistic routing strategy – Leapfrog Routing – for probabilistically contacted DTNs where nodes encounter or contact in some fixed probabilities. We deduce the iterative computation formulate of minimum expected opportunistic delivery delay from each node to the destination, and discover that under the optimal opportunistic routing strategy, messages would be delivered from high-delay node to low-delay node in the leapfrog manner. Rigorous theoretical analysis shows that such a routing strategy is exactly the optimal among all possible ones. Moreover, we apply the idea of Reverse Dijkstra algorithm to design an algorithm. When a destination is given, this algorithm can determine for each node the routing selection function under the Leapfrog Routing strategy. The computation overhead of this algorithm is only O(n ²) where n is the number of nodes in the network. In addition, through extensive simulations based on real DTN traces, we demonstrate that our algorithm can significantly outperform the previous ones.     

Approximate bounds and expressions for the link utilization of shortest-path multicast network traffic

Multicast network traffic is information with one source node, but many destination nodes. Rather than setting up individual connections between the source node and each destination node, or broadcasting the information to the entire network, multicasting efficiently exploits link capacity by allowing the source node to transmit a small number of copies of the information to mutually-exclusive groups of destination nodes. Multicasting is an important topic in the fields of networking (video and audio conferencing, video on demand, local-area network interconnection) and computer architecture (cache coherency, multiprocessor message passing). In this paper, we derive approximate expressions for the minimum cost (in terms of link utilization) of shortest-path multicast traffic in arbitrary tree networks. Our results provide a theoretical best-case scenario for link utilization of multicast distribution in tree topologies overlaid onto arbitrary graphs. In real networks such as the Internet MBONE, multicast distribution paths are often tree-like, but contain some cycles for purposes of fault tolerance. We find that even for richly-connected graphs such as the shufflenet and the hypercube, our expression provides a good prediction of the cost (in terms of link utilization) of multicast communication. Thus, this theoretical result has two applications: (1) a lower bound on the link capacity required for multicasting in random tree topologies, and (2) an approximation of the cost of multicasting in regular LAN and MAN topologies.     

移动自组网中基于移动预测和概率的能量有效组播路由算法

移动自组网中节点的使用寿命很大程度上依赖于电池能量的有效利用．通过研究移动节点能量的剩余和使用情况，提出了一种新的关于节点能量估价函数PCF（power cost function）计算方法，能够较好地反映当前节点的能耗值．并且结合PCF提出一种基于移动预测和概率构造能量有效组播树M-REMiT（an algorithm based on mobility prediction and probability for refining energy-efficient multicast tree）的分布式算法，在节点移动的情况下，利用概率优化方法减少一棵组播树的总能量消耗，延长了组播树中每个节点的使用寿命．模拟结果显示这个组播算法比以前相关的算法具有更好的性能．     

ML-SOR: Message routing using multi-layer social networks in opportunistic communications

Opportunistic networks are a generalization of DTNs in which disconnections are frequent and encounter patterns between mobile devices are unpredictable. In such scenarios, message routing is a fundamental issue. Social-based routing protocols usually exploit the social information extracted from the history of encounters between mobile devices to find an appropriate message relay. Protocols based on encounter history, however, take time to build up a knowledge database from which to take routing decisions. While contact information changes constantly and it takes time to identify strong social ties, other types of ties remain rather stable and could be exploited to augment available partial contact information. In this paper, we start defining a multi-layer social network model combining the social network detected through encounters with other social networks and investigate the relationship between these social network layers in terms of node centrality, community structure, tie strength and link prediction. The purpose of this analysis is to better understand user behavior in a multi-layered complex network combining online and offline social relationships. Then, we propose a novel opportunistic routing approach ML-SOR (Multi-layer Social Network based Routing) which extracts social network information from such a model to perform routing decisions. To select an effective forwarding node, ML-SOR measures the forwarding capability of a node when compared to an encountered node in terms of node centrality, tie strength and link prediction. Trace driven simulations show that a routing metric combining social information extracted from multiple social network layers allows users to achieve good routing performance with low overhead cost.     

Evolutionary forwarding games in delay tolerant networks: Equilibria,mechanism design and stochastic approximation

In this paper, we apply evolutionary games to non-cooperative forwarding control in Delay Tolerant Networks (DTNs). The main focus is on mechanisms to rule the participation of the relays to the delivery of messages in DTNs. Thus, we express the success probability as a function of the competition that takes place within a large population of mobiles, and we characterize the effect of reward-based mechanisms on the performance of such systems. Devices acting as active relays, in fact, sacrifice part of their batteries in order to support message replication and thus increase the probability to reach the destination. In our scheme, a relay can choose the strategy by which they participate to the message relaying. A mobile that participates receives a unit of reward based on the reward mechanism selected by the network. A utility function is introduced as the difference between the expected reward and the energy cost, i.e., the cost spent by the relay to sustain forwarding operations. We show how the evolution dynamics and the equilibrium behavior (called Evolutionary Stable Strategy – ESS) are influenced by the characteristics of inter contact time, energy expenditure and pricing characteristics.We extend our analysis to mechanisms that the system can introduce in order to have the message delivered to the destination with high probability within a given deadline and under energy constraints which bound the number of released copies per message. Finally, we apply our findings in order to devise decentralized forwarding algorithms that are rooted in the theory of stochastic approximations. Thus, we demonstrate that the ESS can be attained without complete knowledge of the system state and letting the source monitor number of released copies per message only. We provide extensive numerical results to validate the proposed scheme.     

基于能量收集技术的无线协作网络中继选择

针对目前能量收集技术能够收集到的可用能量受限,导致无线协作网络中继节点处易出现能量短板的问题,为了避免整个网络因中继节点大量死亡而瘫痪,提出了一种基于能量收集技术的无线协作网络中继选择方案,即联合最大能量和最大数据传输链路的中继选择方案。首先,基于节点的能量收集状况,选出每跳中能量最大的节点进行解码转发;然后,结合每连续两跳的链路传输状态,选出与源节点和目的节点之间的数据传输信道最优者作为中继节点。结合Nakagami-m信道衰落模型,将该方案与随机选择方案、最大数据链路信道增益(MaDs)方案和基于中继-窃听链路最小信道增益(BNBF)方案进行对比分析,结果表明:在满足收集的能量足够用于下一时隙能量收集和数据传输的前提下,用于能量收集的比例越小,网络中断概率越小;联合最大能量和最大数据传输链路的中继选择方案在网络中断性能方面优于其他方案,其中断概率随信噪比的增大而减小,特别是当平均信噪比为38dB时,网络中断概率降到10^-5。     

Improving routing protocol performance in delay tolerant networks using extended information

Delay tolerant networks (DTNs) are wireless mobile networks that do not guarantee the existence of a path between a source and a destination at any time. When two nodes move within each other’s transmission range during a period of time, they can contact each other. The contact of nodes can be periodical, predictable and nonpredictable. In this paper, we assume the contact of nodes is nonpredictable so that it can reflect the most flexible way of nodes movement. Due to the uncertainty and time-varying nature of DTNs, routing poses special challenges. Some existing schemes use utility functions to steer the routing in the right direction. We find that these schemes do not capture enough information of the network. Thus, we develop an extended information model that can capture more mobility information and use regression functions for data processing. Experimental results from both our own simulator and real wireless trace data show that our routing algorithms based on the extended information model can increase the delivery ratio and reduce the delivery latency of routing compared with existing ones.     

移动Ad Hoc网络的可靠多播路由协议

在移动Ad Hoc网络环境中，分组的重传和路由的重构比有线网络更频繁。在网络多播树变化的情况下提供高的分组传输率是移动Ad Hoc网络多播路由的主要难题。文中提出了一种基于协议转接概念的移动Ad Hoc网络的可靠多播路由协议(RMRP)，该协议较好地减少了移动Ad Hoc网络中大量的路由重构和数据分组的重传。仿真实验显示RMRP具有较高的传输率和较低的端到端分组延迟。     

Architectural support for efficient multicasting in irregularnetworks

Parallel computing on networks of workstations is fast becoming a cost-effective high-performance computing alternative to MPPs. Such a computing environment typically consists of processing nodes interconnected through a switch-based irregular network. Many of the problems that were solved for regular networks have to be solved anew for these systems. One such problem is that of efficient multicast communication. In this paper, we propose two broad categories of schemes for efficient multicasting in such irregular networks: network interface-based (NI-based) and switch-based. The NI-based multicasting schemes use the network interface of intermediate destinations for absorbing and retransmitting messages to other destinations in the multicast tree. In contrast, the switch-based multicasting schemes use hardware support for packet replication at the switches of the network and a concept known as multidestination routing to convey a multicast message from one source to multiple destinations. We first present alternative schemes for efficient multipacket forwarding at the NI and derive an optimal k-binomial multicast tree for multipacket NI-based multicast. We then propose two switch-based multicasting schemes that differ in the power of the encoding scheme and the complexity of the decoding logic at the switches. These multicasting schemes use path-based multidestination worms that can cover all nodes connected to switches along a valid unicast path and tree-based multidestination worms that can cover entire destination sets in a single phase using one worm, respectively. For each scheme, we describe the associated header encoding and decoding operation, the method for deriving multidestination worms that cover arbitrary multicast destination sets, and the multicasting scheme using the derived multidestination worms