Adaptive Multimodule Routers for Multiprocessor Architectures

Recent multiprocessors such as Cray T3D support interprocessor communication using partitioned dimension-order routers (PDRs). In a PDR implementation, the routing logic and switching hardware is partitioned into multiple modules, with each module suitable for implementation as a chip. This paper proposes a method to incorporate adaptivity into such routers with simple changes to the router structure and logic. We show that with as few as two virtual channels per physical channel, adaptivity can be provided to handle nonuniform traffic in multidimensional meshes.     

Fault-tolerant wormhole routing for hypercube networks

We present an adaptive fault-tolerant wormhole routing algorithm for hypercubes by using 3 virtual networks. The routing algorithm can tolerate at least n−1 faulty nodes and can route a message via a path of length no more than the shortest path plus four. Previous algorithms which achieve the same fault tolerant ability need 5 virtual networks. Simulation results are also given in this paper.     

An efficient void resolution method for geographic routing in wireless sensor networks

Geographic routing is an attractive choice for routing data in wireless sensor networks because of lightweight and scalable characteristics. Most geographic routing approaches combine a greedy forwarding scheme and a void resolution method to detour a void area that has no active sensor. The previous solutions, including the well-known GPSR protocol, commonly use the right-hand rule for void resolution. However, the detour path produced by the right-hand rule is not energy-efficient in many cases. In this paper, we propose a new void resolution method, called void resolution-forwarding, which can overcome voids in the sensor network energy-efficiently. It exploits the quadrant-level right-hand rule to select the next hop for the current node during circumventing a void area. We show by experiments that the proposed method is efficient and scalable with respect to the various voids and network density and that it outperforms the GPSR protocol significantly.     

Compressionless wormhole routing: an analysis for hypercube with virtual channels

Several recent studies have shown that adaptive routing algorithms based on deadlock recovery have superior performance characteristics than those based on deadlock avoidance. Most of these studies, however, have relied on software simulation due to the lack of analytical modelling tools. In an effort towards filling this gap, this paper presents a new analytical model of compressionless routing in wormhole-routed hypercubes. This routing algorithm exploits the tight coupling between wormhole routers for flow control to detect and recover from potential deadlock situations. The advantages of compressionless routing include deadlock-free adaptive routing with no extra virtual channels, simple router design, and order-preserving message transmission. The proposed analytical model computes message latency by determining the message transmission time, blocking delay at each router, multiplexing delay at each network channel, and waiting time in the source before entering the network. The validity of the model is demonstrated by comparing analytical results with those obtained through simulation experiments.     

An efficient algorithm for group multicast routing with bandwidth reservation

Multicasting refers to the transmission of data from a source node to multiple destination nodes in a network. Group multicasting is a generalisation of multicasting whereby every member of a group is allowed to multicast messages to other members that belong to the same group. The routing problem in this case involves the construction of a set of low cost multicast trees with bandwidth requirements, one for each member of the group, for multicasting messages to other members of the group. In this paper, we propose a new heuristic algorithm to generate a set of low cost multicast trees with bandwidth requirements. Simulation results show that our proposed algorithm performed better in terms of cost and in terms of utilisation of bandwidth as compared to an existing algorithm that was proposed by Jia and Wang [3].     

A fault-tolerant wormhole routing scheme for torus networks with nonconvex faults

In this paper, we present a fault-tolerant routing algorithm for torus networks by using only 4 virtual channels. The proposed algorithm is based on the solid fault model, which includes rectangular faults and many practical nonconvex faults. Previous works need at least 6 virtual channels to achieve the same fault-tolerant ability.     

Accelerating incremental checkpointing for extreme-scale computing

Concern is beginning to grow in the high-performance computing (HPC) community regarding the reliability of future large-scale systems. Disk-based coordinated checkpoint/restart has been the dominant fault tolerance mechanism in HPC systems for the past 30 years. Checkpoint performance is so fundamental to scalability that nearly all capability applications have custom checkpoint strategies to minimize state and reduce checkpoint time. One well-known optimization to traditional checkpoint/restart is incremental checkpointing, which has a number of known limitations. To address these limitations, we describe libhashckpt, a hybrid incremental checkpointing solution that uses both page protection and hashing on GPUs to determine changes in application data with very low overhead. Using real capability workloads and a model outlining the viability and application efficiency increase of this technique, we show that hash-based incremental checkpointing can have significantly lower overheads and increased efficiency than traditional coordinated checkpointing approaches at the scales expected for future extreme-class systems.     

An efficient multipath routing for distributed computing systems with data replication

In distributed computing environments, executing a program often requires the access of remote data files. An efficient data routing scheme is thus important for time-critical applications. To ensure a prior desired communication quality, we present a connection-oriented routing scheme, the multipath routing, which allows multiple routes to be established between the source and the destination. Based on the multipath routing scheme, the problem of finding a collection of routing paths for an application to minimize its data transmission time is addressed. Such a problem becomes a complex combinatorial one when the application accesses multiple replicated data sources. Since finding an optimal solution is computationally infeasible in practice, we thus propose a heuristic method to get a sub-optimal solution.     

Partitioning and mapping of nested loops for linear array multicomputers

In distributed-memory multicomputers, minimizing interprocessor communication is the key to the efficient execution of parallel programs. In order to reduce the amount of communication overhead, parallel programs on multicomputers must be carefully scheduled by parallelizing compilers. This paper proposes some compilation techniques for partitioning and mapping nested loops with constant data dependences onto linear array multicomputers. First, a systematic partition strategy is proposed to project ann-dimensional computational structure, representing ann-nested loop, onto a line to form a one-dimensional projected structure with low communication overhead. Then, a mapping algorithm is proposed for mapping the partitioned loops onto linear arrays in a way that balances the workload and minimizes the communication cost among processors. Finally, parallel execution codes can be automatically generated for such linear array multicomputers.     

Task migration in all-port wormhole-routed 2D mesh multicomputers

In a mesh multicomputer, submeshes are allocated to perform jobs according to processor allocation schemes, with each task assigned to occupy processors of one submesh with an appropriate size. To assign regions for incoming tasks, task compaction is needed to produce a large contiguous free region. The overhead of task compaction relies mainly on designing an efficient task migration scheme. This paper investigates task migration schemes in 2D wormhole-routed mesh multicomputers with an all-port communication model. Two constraints are given between two submeshes for task migration. Two task migration schemes that follow one of the constraints in 2D mesh multicomputers are then developed. In addition, the proposed schemes are proven to be deadlock-free and congestion-free. Finally, performance analysis is adopted to compare the proposed task migration schemes.     

基于Ad Hoc的虫洞攻击与防御研究综述

本文在分析无线Ad Hoc网络路由协议研究现状的基础上,指出无线Ad Hoc网络路由协议存在的脆弱性及针对协议漏洞所发起的几种主要攻击形式。重点分析虫洞攻击的基本原理及其当前的防御方法和不足,为今后更进一步研究安全路由协议打下基础。     

Concurrent face traversal for efficient geometric routing

We present a concurrent face routing CFR algorithm. We formally prove that the worst case latency of our algorithm is asymptotically optimal. Our simulation results demonstrate that, on average, the path stretch, i.e., the speed of message delivery, achieved by CFR is significantly better than by other known geometric routing algorithms. In fact, it approaches the shortest possible path. CFR maintains its advantage over the other algorithms in pure form as well as in combination with greedy routing. CFR displays this performance superiority both on planar and non-planar graphs.     

Minimal fully adaptive wormhole routing on hypercubes

Wormhole routing is an advanced switching technique used in new generation multicomputers. Since such a machine may suffer serious performance degradation under heavy or uneven traffic load, an adaptive routing method is particularly called upon. In minimal fully adaptive routing, the paths between any source and destination pair to be used are exactly all the shortest paths. We propose in this paper a minimal fully adaptive routing algorithm for n-dimensional hypercube with (n+1)/2 virtual channels per physical channel.     

Explanation of Performance Degradation in Turn Model

The Turn model routing algorithms for mesh interconnection network achieve partial adaptivity without any virtual channels. However, the routing performance measured by simulations is worse than with the simple deterministic routing algorithm. Authors have explained these results simply by uneven dynamic load through the network. However, this phenomenon has not been studied further. This paper investigates performance degradation with Turn model and drawbacks of partially adaptive routing in comparison with the deterministic routing, and it introduces some new concepts. Our simulations deal with individual channels and results are presented by 3D graphs, rather than by commonly used averages. An additional parameter—channel occupation, which is consistent with queuing theory commonly used in many proposed analytical models, is introduced. We also propose a new structure, the Channel Directions Dependency Graph (CDDG). It provides a new approach in analysis, helps in understanding of dynamic routing behaviour, and it can be generalized in other routing algorithms.     

An optimistic checkpointing and message logging approach for consistent global checkpoint collection in distributed systems

Checkpointing and rollback recovery are widely used techniques for achieving fault-tolerance in distributed systems. In this paper, we present a novel checkpointing algorithm which has the following desirable features: A process can independently initiate consistent global checkpointing by saving its current state, called a tentative checkpoint. Other processes come to know about a consistent global checkpoint initiation through information piggy-backed with the application messages or limited control messages if necessary. When a process comes to know about a new consistent global checkpoint initiation, it takes a tentative checkpoint after processing the message (not before processing the message as in existing communication-induced checkpointing algorithms). After a process takes a tentative checkpoint, it starts logging the messages sent and received in memory. When a process comes to know that every other process has taken a tentative checkpoint corresponding to current consistent global checkpoint initiation, it flushes the tentative checkpoint and the message log to the stable storage. The tentative checkpoints together with the message logs stored in the stable storage form a consistent global checkpoint. Two or more processes can concurrently initiate consistent global checkpointing by taking a new tentative checkpoint; in that case, the tentative checkpoints taken by all these processes will be part of the same consistent global checkpoint. The sequence numbers assigned to checkpoints by a process increase monotonically. Checkpoints with the same sequence number form a consistent global checkpoint. We also present the performance evaluation of our algorithm.     

Self-stabilizing algorithm for checkpointing in a distributed system

If the variables used for a checkpointing algorithm have data faults, the existing checkpointing and recovery algorithms may fail. In this paper, self-stabilizing data fault detecting and correcting, checkpointing, and recovery algorithms are proposed in a ring topology. The proposed data fault detection and correction algorithms can handle data faults; at most one per process, but in any number of processes. The proposed checkpointing algorithm can deal with concurrent multiple initiations of checkpointing and data faults. A process can recover from a fault, using the proposed recovery algorithm in spite of multiple data faults present in the system. All the proposed algorithms converge in O(n)$O(n)$ steps, where n$n$ is the number of processes. The algorithm can be extended to work for general topologies too.     

An efficient protocol for checkpointing recovery in distributedsystems

The authors present an efficient synchronized checkpointing protocol that exploits the dependency relation between processes in distributed systems. In this protocol, a process takes a checkpoint when it knows that all processes on which it computationally depends took their checkpoints, hence the process need not always wait for the decision made by the checkpointing coordinator as in the conventional synchronized protocols. As a result, the checkpointing coordination time is substantially reduced and the possibility of total abort of the checkpointing coordination is reduced     

PRDT（2，1）架构的NoC系统容错路由算法

链路和节点的故障会导致网络中许多节点无法相互通讯,因此容错性是NoC系统设计中的一个重要问题。基于一种新的NoC网络拓扑结构PRDT（2,1）,提出一种PRDT（2,1）容错路由算法以及相应的节点失效算法。节点失效算法通过使较少数量的无故障节点失效来构造矩形故障区域,PRDT（2,1）容错路由算法仅使用了最小数量的虚拟通道并提供足够的自适应性以实现无死锁容错路由。只要故障区域没有断开网络,这一算法能够保证路由的连通性。算法在不同故障率的PRDT（2,1）网络中仿真,结果显示这一算法具有良好的平滑降级使用特性。     

Performance evaluation of deterministic wormhole routing in k-ary n-cubes

We present a new analytical approach for the performance evaluation of deterministic wormhole routing in k-ary n-cubes. Our methodology achieves closed formulas for average time values through the analysis of network flows. The comparison with simulation models demonstrates that our methodology gives accurate results for both low and high traffic conditions. Another important quality is the flexibility of our approach. We demonstrate that it can be used to model dimension-ordered-routing in several k-ary n-cubes such as hypercubes, 3D symmetric and asymmetric tori, architectures with uni- and bi-directional channels.     

Adaptive wormhole routing in tori with faults: A mathematical approach

Fault-tolerance in a communication network is defined as the ability of the network to effectively utilize its redundancy in the presence of faulty components (i.e., nodes or links). New technologies of integration now enable the design of computing systems with hundreds and even thousands of independent processing elements which can cooperate on the solution of the same problem for a corresponding improvement in the execution time. However, as the number of processing units increases, concerns for reliability and continued operation of the system in the presence of failures must be addressed. Adaptive routing algorithms have been frequently suggested as a means of improving communication performance in large-scale massively parallel computers, Multiprocessors System-on-Chip (MP-SoCs), and peer-to-peer communication networks. Before such schemes can be successfully incorporated in networks, it is necessary to have a clear understanding of the factors which affect their performance potential. This paper proposes a novel analytical model to investigate the performance of five prominent adaptive routings in wormhole-switched 2-D tori fortified with an effective scheme suggested by Chalasani and Boppana [S. Chalasani, R.V. Boppana, Adaptive wormhole routing in tori with faults, IEE Proc. Comput. Digit. Tech. 42(6) (1995) 386–394], as an instance of a fault-tolerant method widely used in the literature to achieve high adaptivity and support inter-processor communications in parallel computers. Analytical approximations of the model are confirmed by comparing them with those obtained through simulation experiments.