A Read-Only Distributed Hash Table

A distributed hash table (DHT) is an infrastructure to support resource discovery in large distributed systems. In a DHT, data items such as resources, indexes of resources or resource metadata, are distributed across an overlay network based on a hash function. However, this may not be desirable in commercial applications such as Grid and cloud computing whereby the presence of multiple administrative domains leads to the issues of data ownership and self-economic interests. In this paper, we present R-DHT (Read-only DHT), a DHT-based resource discovery scheme without distributing data items. To map each data item back onto its resource owner, a physical host, we virtualize each host into virtual nodes. Nodes are further organized as a segment-based overlay network which increases node failure resiliency without replicating data items. We demonstrate the feasibility of our proposed scheme by presenting R-Chord, an implementation of R-DHT using Chord as the underlying overlay graph, with lookup and maintenance optimizations. Through analytical and simulation analyses, we evaluate the performance of R-DHT and compare it with traditional DHTs in terms of lookup path length, resiliency to node failures, and maintenance overhead. Overall, we found that R-DHT is effective and efficient for resource indexing and discovery in large distributed systems with a strong commercial requirement.     

Stability–throughput tradeoff and routing in multi-hop wireless ad hoc networks

We study the throughput of multi-hop routes and stability of forwarding queues in a wireless ad-hoc network with random access channel. We focus on a wireless network with static nodes, such as community wireless networks. Our main result is characterization of stability condition and the end-to-end throughput using the balance rate. We also investigate the impact of routing on end-to-end throughput and stability of intermediate nodes. We show that (i) as long as the intermediate queues in the network are stable, the end-to-end throughput of a connection does not depend on the load on the intermediate nodes, (ii) we show that if the weight of a link originating from a node is set to the number of neighbors of this node, then shortest-path routing maximizes the minimum probability of end-to-end packet delivery in a network of weighted fair queues. Numerical results are given and support the results of the analysis. Finally, we perform extensive simulation and verify that the analytical results closely match the results obtained from simulations.     

Improving Query Response Delivery Quality in Peer-to-Peer Systems

Unstructured peer-to-peer (P2P) system is the prevalent model in today's P2P systems. In such systems, a response is sent along the same path that carried the incoming query message. To guarantee the anonymity of the requestor, no requestor information is included in the response message, and each node in the query's incoming path only knows its direct neighbors who sent the query request to it. This mechanism introduces response loss when any one node or connection in the path fails, which is a common occurrence in the P2P system due to its dynamic feature. In this paper, we address the response loss problem and show that peers' oscillation can cause up to a 35 percent response loss in an unstructured P2P system. We also present three techniques to alleviate this problem: the redundant response delivery (RRD) scheme as a proactive approach, the adaptive response delivery (ARD) scheme as a reactive approach, and the extended adaptive response delivery scheme to render ARD to function in an unstructured P2P system with limited or no flooding-based search mechanism. We have evaluated our techniques in a large-scale network simulation. With limited traffic overhead, all three techniques reduce response loss rate by more than 65 percent and are fully distributed. We have designed our techniques to be simple to develop and implement in existing P2P systems     

Using Data Accessibility for Resource Selection in Large-Scale Distributed Systems

Large-scale distributed systems provide an attractive scalable infrastructure for network applications. However, the loosely coupled nature of this environment can make data access unpredictable, and in the limit, unavailable. We introduce the notion of accessibility to capture both availability and performance. An increasing number of data-intensive applications require not only considerations of node computation power but also accessibility for adequate job allocations. For instance, selecting a node with intolerably slow connections can offset any benefit to running on a fast node. In this paper, we present accessibility-aware resource selection techniques by which it is possible to choose nodes that will have efficient data access to remote data sources. We show that the local data access observations collected from a node's neighbors are sufficient to characterize accessibility for that node. By conducting trace-based, synthetic experiments on PlanetLab, we show that the resource selection heuristics guided by this principle significantly outperform conventional techniques such as latency-based or random allocations. The suggested techniques are also shown to be stable even under churn despite the loss of prior observations.     

A proximity-aware load balancing in peer-to-peer-based volunteer computing systems

One of the main challenges in peer-to-peer-based volunteer computing systems is an efficient resource discovery algorithm. Load balancing is a part of resource discovery algorithm and aims to minimize the overall response time of the system. This paper introduces an analytical model based on distributed parallel queues to optimize the average response time of the system in a distributed manner. The proposed resource discovery algorithm consists of two phases. In the first phase, it selects peers in a load-balanced manner based on QoS constraints of request. In the second phase, a proximity-aware feature is applied to select the peer with minimum communication overhead among selected peers in the first phase. Two dispatching strategies are proposed for the load balancing based on stochastic analysis of routing in the distributed parallel queues. These policies adopt probabilistic and deterministic sequences to redirect requests to the capable peers in the system. Simulation results show that the proposed resource discovery algorithm improves the response time of user’s requests by a factor of 1.8 under a moderate load.     

基于动态膜计算系统的自组织网络广播算法

应用仿生学原理设计了一种新型的广播算法——基于动态膜计算系统的广播算法,提出了动态膜计算系统,并给出了解决自组织网络中广播问题的规则集。系统中节点转播信息的优先权通过节点间距离及邻居个数确定,适合不同密度的网络;并根据信息数与门限值的比较,取消部分节点的转播权,从而提高了可达率和转播节省率。仿真测试验证了此系统用于广播是可行的、高效的,为设计无线自组织网络中的广播算法提供了新思路。     

Applying Peer-to-Peer Techniques to Grid Replica Location Services

Peer-to-peer systems offer attractive system management properties, including the ability of components that join the network to self-organize; scalability up to tens of thousands of members; the ability of the network to automatically repair its topology after node failures; and techniques for maintaining redundant information to improve reliability and load balancing. We investigate applying peer-to-peer techniques to Grid services that are oriented toward resource discovery. In particular, we apply the Chord structured peer-to-peer overlay network to the Globus Replica Location Service, which allows registration and discovery of data replicas. We describe the design and performance of a Peer-to-Peer Replica Location Service (P-RLS) that uses the Chord algorithm to self-organize P-RLS servers and exploits the Chord overlay network to replicate P-RLS mappings adaptively. We present performance measurements and simulation results for the P-RLS system. We also discuss outstanding issues for applying peer-to-peer techniques to Grid resource discovery services.     

CycloidGrid: A proximity-aware P2P-based resource discovery architecture in volunteer computing systems

Volunteer computing which benefits from idle cycles of volunteer resources over the Internet can integrate the power of hundreds to thousands of resources to achieve high computing power. In such an environment the resources are heterogeneous in terms of CPU speed, RAM, disk capacity, and network bandwidth. So finding a suitable resource to run a particular job becomes difficult. Resource discovery architecture is a key factor for overall performance of peer-to-peer based volunteer computing systems. The main contribution of this paper is to develop a proximity-aware resource discovery architecture for peer-to-peer based volunteer computing systems. The proposed resource discovery algorithm consists of two stages. In the first stage, it selects resources based on the requested quality of service and current load of peers. In the second stage, a resource with higher priority to communication delay is selected among the discovered resources. Communication delay between two peers is computed by a network model based on queuing theory, taking into account the background traffic of the Internet. Simulation results show that the proposed resource discovery algorithm improves the response time of user’s requests by a factor of 4.04 under a moderate load.     

Peer-to-peer systems for discovering resources in a dynamic grid

The convergence of the Grid and Peer-to-Peer (P2P) worlds has led to many solutions that try to efficiently solve the problem of resource discovery on Grids. Some of these solutions are extensions of P2P DHT-based networks. We believe that these systems are not flexible enough when the indexed data are very dynamic, i.e., the values of the resource attributes change very frequently over time. This is a common case for Grid metadata, like CPU loads, queue occupation, etc. Moreover, since common requests for Grid resources may be expressed as multi-attribute range queries, we think that the DHT-based P2P solutions are poorly flexible and efficient in handling them.In this paper we present two P2P systems. Both are based on Routing Indexes, which are used to efficiently route queries and update messages in the presence of highly variable data. The first system uses a tree-shaped overlay network. The second one is an evolution of the first, and is based on a two-level hierarchical network topology, where tree topologies must only be maintained at the lower level of the hierarchy, i.e., within the various node groups making up the network. The main goal of the second organization is to achieve a simpler maintenance of the overall P2P graph topology, by preserving the good properties of the tree-shaped topology.We discuss the results of extensive simulation studies aimed at assessing the performance and scalability of the proposed approaches. We also analyze how the network topologies affect the propagation of query and update messages.     

一种双网同步搜索的虚拟网络映射算法

针对虚拟网络映射中的资源分配问题,通过建立双网同步搜索映射模型,采用普里姆最小生成树算法思想,同步搜索虚拟网络中的待映射虚拟节点和物理网络中的可映射物理节点,将相邻的虚拟节点依次映射到邻接的物理节点上,协调完成节点及其邻接链路的映射操作,使虚拟网络映射具有拓扑一致性。仿真实验表明,提出的DS-VNM算法能有效地降低虚拟链路的映射路径长度,提高网络收益与网络代价比、虚拟网络请求接受率,获得了较好的资源分配性能。     

Secure Node Discovery in Ad-hoc Networks and Applications

Designing secure protocols over ad-hoc networks has proved to be a very challenging task, due to various features of such networks, such as partial connectivity, node mobility, and resource constraints. Furthermore, their lack of physical infrastructures deprives their users of even basic network functions such as message routing, for which nodes are themselves responsible.In this paper we consider a very basic network function, node discovery, in ad-hoc networks, where a node with limited network information would like to establish a session with a given number of other nodes in the network (of which the node may not be aware about). We formally define correctness, security and efficiency properties of node discovery protocols, and investigate the problem of designing such protocols under appropriate network topology assumptions. Here, the security of these protocols is against Byzantine adversaries that can corrupt up to a limited number of nodes in the network and make them arbitrarily deviate from their protocol. After presenting some secure node discovery protocols, we show their application to secure service architectures in ad-hoc networks.     

Maintaining censorship resistance in the iTrust network for publication,search and retrieval

This paper presents the architecture of the iTrust system together with algorithms for maintaining censorship resistance. In iTrust, metadata describing documents, and requests containing keywords, are distributed to randomly chosen nodes in the iTrust network. If a node receives a request containing keywords that match metadata it holds, it sends the URL of the matching document to the requesting node, which then retrieves the document from the source node. A novel detection algorithm estimates the proportion of operational nodes in the iTrust network, by comparing the empirical probabilities of the number of responses received for a node’s request with the analytical probabilities for a match, for various proportions of operational nodes. A novel defensive adaptation algorithm increases the number of nodes to which the requests are distributed, in order to maintain the same high probability of a match when some of the nodes are non-operational or malicious as when all of the nodes are operational. Extensive experimental evaluations demonstrate the effectiveness of the architecture and the algorithms for maintaining censorship resistance in the iTrust network.     

Detecting Sybil attacks in Wireless Sensor Networks using neighboring information

As the prevalence of Wireless Sensor Networks (WSNs) grows in the military and civil domains, the need for network security has become a critical concern. In a Sybil attack, the WSN is subverted by a malicious node which forges a large number of fake identities in order to disrupt the network’s protocols. In attempting to protect WSNs against such an attack, this paper develops a scheme in which the node identities are verified simply by analyzing the neighboring node information of each node. The analytical results confirm the efficacy of the approach given a sufficient node density within the network. The simulation results demonstrate that for a network in which each node has an average of 9 neighbors, the scheme detects 99% of the Sybil nodes with no more than a 4% false detection rate. The experiment result shows that the Sybil nodes can still be identified when the links are not symmetric.     

Neighbor discovery for wireless networks via compressed sensing

This paper studies the problem of neighbor discovery in wireless networks, namely, each node wishes to discover and identify the network interface addresses (NIAs) of those nodes within a single hop. A novel paradigm, called compressed neighbor discovery is proposed, which enables all nodes to simultaneously discover their respective neighborhoods with a single frame of transmission, which is typically of a few thousand symbol epochs. The key technique is to assign each node a unique on–off signature and let all nodes simultaneously transmit their signatures. Despite that the radios are half-duplex, each node observes a superposition of its neighbors’ signatures (partially) through its own off-slots. To identify its neighbors out of a large network address space, each node solves a compressed sensing (or sparse recovery) problem.Two practical schemes are studied. The first employs random on–off signatures, and each node discovers its neighbors using a noncoherent detection algorithm based on group testing. The second scheme uses on–off signatures based on a deterministic second-order Reed–Muller code, and applies a chirp decoding algorithm. The second scheme needs much lower signal-to-noise ratio (SNR) to achieve the same error performance. The complexity of the chirp decoding algorithm is sub-linear, so that it is in principle scalable to networks with billions of nodes with 48-bit IEEE 802.11 MAC addresses. The compressed neighbor discovery schemes are much more efficient than conventional random-access discovery, where nodes have to retransmit over many frames with random delays to be successfully discovered.     

Virtual network mapping algorithm in the cloud infrastructure

Network virtualization has received considerable attention recently because a Cloud Provider (CP) that is responsible for deploying a substrate network in the cloud infrastructure uses network virtualization to support multiple Virtual Network (VN) requests over the shared substrate network. However, mapping multiple VN requests with constraints on virtual nodes and virtual links into a shared substrate network presents a significant challenge, and is considered an NP-hard problem. In this paper, we propose a heuristic mapping algorithm that handles online VN requests. The node mapping algorithm selects a substrate node for mapping that satisfies both a virtual node's resource requirement and its amount of requested bandwidth. The link mapping algorithm either maps a virtual link to the shortest substrate path that satisfies the requested bandwidth of the virtual link or uses the cut-shortest path approach to map a virtual link to multiple substrate paths that satisfy the requested bandwidth of the virtual link. The path migration algorithm migrates virtual links to different substrate paths to maximize the number of accepted VN requests in a substrate network. Simulation results show that the proposed heuristic mapping algorithm uses resources more efficiently, produces more revenue, and has better performance than existing mapping approaches.     

Improved group-based cooperative caching scheme for mobile ad hoc networks

Data caching is a popular technique that improves data accessibility in wired or wireless networks. However, in mobile ad hoc networks, improvement in access latency and cache hit ratio may diminish because of the mobility and limited cache space of mobile hosts (MHs). In this paper, an improved cooperative caching scheme called group-based cooperative caching (GCC) is proposed to generalize and enhance the performance of most group-based caching schemes. GCC allows MHs and their neighbors to form a group, and exchange a bitmap data directory periodically used for proposed algorithms, such as the process of data discovery, and cache placement and replacement. The goal is to reduce the access latency of data requests and efficiently use available caching space among MH groups. Two optimization techniques are also developed for GCC to reduce computation and communication overheads. The first technique compresses the directories using an aggregate bitmap. The second employs multi-point relays to develop a forwarding node selection scheme to reduce the number of broadcast messages inside the group. Our simulation results show that the optimized GCC yields better results than existing cooperative caching schemes in terms of cache hit ratio, access latency, and average hop count.     

Resource allocation in cube network systems based on the coveringradius

When multiple copies of a certain resource exist in a cube network system, it is desirable that every nonresource node can reach the resource in a given number of hops. In this paper, we introduce systematic approaches to resource allocation in a cube system so that each nonresource node is connected with a specified number of resource copies and that the allocation performance measure of interest is optimized. The methodology used is based on the covering radius results of known codes. These codes aid in constructing desired linear codes whose codewords address nodes where resource copies are placed. The resource allocation problem is translated to an integer nonlinear program whose best possible solution can be identified quickly by taking advantage of basic properties derived from the known codes, yielding an optimal or near-optimal allocation result. Those basic properties lead to drastic time complexity reduction (up to several orders of magnitude smaller), in particular for large system sizes. Our approaches are applicable to any cube size, often arriving at more efficient allocation outcomes than what are attainable using prior schemes     

基于网络资源相关性的虚拟网络映射算法

针对网络虚拟化环境中资源利用率较低的问题,通过建立资源相关性度量模型,刻画虚拟节点和物理顶点之间的匹配程度,根据虚拟节点和物理顶点之间的资源相关性,将虚拟节点映射到资源相关性较强的物理顶点上;为了降低虚拟链路的映射路径长度,通过建立节点间邻接关系模型,将相邻的虚拟节点映射到邻接的物理顶点上。实验结果表明,提出的虚拟网络映射算法均衡了物理网络资源的分布状态,降低了虚拟网络映射的资源代价,提高了虚拟网络请求接受率。     

A Distributed and Efficient Flooding Scheme Using 1-Hop Information in Mobile Ad Hoc Networks

Flooding is one of the most fundamental operations in mobile ad hoc networks. Traditional implementation of flooding suffers from the problems of excessive redundancy of messages, resource contention, and signal collision. This causes high protocol overhead and interference with the existing traffic in the networks. Some efficient flooding algorithms were proposed to avoid these problems. However, these algorithms either perform poorly in reducing redundant transmissions or require each node to maintain 2-hop (or more) neighbors information. In the paper, we study the sufficient and necessary condition of 100 percent deliverability for flooding schemes that are based on only 1-hop neighbors information. We further propose an efficient flooding algorithm that achieves the local optimality in two senses: 1) the number of forwarding nodes in each step is minimal and 2) the time complexity for computing forwarding nodes is the lowest, which is O(nlogn), where n is the number of neighbors of a node. Extensive simulations have been conducted and simulation results have shown the excellent performance of our algorithm     

SOA中一种基于负载均衡的服务查找请求路由算法

服务查找是面向服务架构(SOA)中一个非常重要的环节,但目前的服务查找算法一般并未考虑到服务查找节点间的负载均衡,在请求频繁条件下不能满足查找效率的要求。提出一种分布式的、综合考虑节点处理能力和网络延时、适用于SOA中分布式服务注册中心的服务查找请求路由算法HaFA。该算法利用负载度实现对服务节点计算能力的度量,解决了负载度均衡后任务仍可能分配到弱计算能力节点上的问题,提高了服务注册中心计算资源的利用率;利用节点负载波动率估量下一个离散时间点的负载度,解决了网络延时期间负载波动对实现均衡造成影响的问题。实验结果表明,HaFA在分布式服务查找中能有效提高系统吞吐率,缩短结果响应的平均等待时间。