Improved Algorithms for Balanced Ring Formation for Fault Tolerance in A 2D Mesh

Fault ring (f-ring) is a popular model for the fault tolerance in grid based architectures such as 2D-mesh and torus. In the work proposed by Huxi Gu et al. introduced the concept of a balanced ring( b-ring) to reduce the traffic load on the fault ring to achieve fault tolerance in a mesh architecture. However, central to their work is the formation of the balanced ring that surrounds a fault ring. In this paper, we propose a new distributed approach for the formation of the balanced ring. Our approach is based on eight-neighborhood property that requires only the local information of the faulty nodes in contrast to the global knowledge as needed by the algorithm.

Cluster networks are seen as the future access networks for multimedia streaming, e-commerce, network storage, etc. For these applications, performance and high availability are particularly crucial. Regular topologies are preferred when performance is the primary concern. However, due to spatial constraints or fault-related issues, the network structure may become irregular, which makes more difficult to find deadlock-free minimal paths. Over the recent years, several solutions have been proposed. One of them is the LASH routing, which enables minimal routing by assigning paths to different virtual layers. In this paper, we propose an extension of LASH in order to reduce the number of required virtual layers by allowing transitions between virtual layers. Evaluation results show that the new routing scheme (LASH-TOR) is able to obtain full minimal routing with a reduced number of virtual channels. For torus and mesh networks, with only two virtual channels, LASH throughput is increased by an average factor of improvement of 3.30 for large networks. For regular networks with some unconnected (faulty) links, equal performance improvements are achieved. Even for highly irregular networks of size up to 128 switches the new routing scheme only needs three virtual channels for guaranteeing minimal routing. Besides, LASH-TOR performs well compared to dimension order routing for mesh and torus networks.

An efficient all-to-all communication algorithm for torus and mesh networks, A2AT, was proposed. A2AT schedules message sending sequence so that all links are fully used by exploiting function of concurrent message transfer in the node. By using A2AT, the hop count of messages equals the maximum number of messages sharing a link in their routes for all message transfers. A2AT can therefore maintain synchronization without the need for phasing operation such as an MPI barrier. When the VOQ which is an ideal configuration for A2AT was used, communication times for mesh/torus network obtained by A2AT were roughly 1.20 and 1.09 times higher, on average, than those of the ideal times. When the networks had the minimum number of virtual channels and a small buffer, assuming a practical network, A2AT was able to reduce communication times by 12.5% and 36.0% compared with those of the conventional algorithm. When two controllers are used, A2AT reduced 28.2% and 55.7% communication time with those by A2AND on 15x15x15 (=3,375 nodes) mesh and torus networks respectively (18.6% and 44.8% in average). A2AT also reduced 15.1% and 41.9% of communication time with those by A2AND on the same mesh and torus networks respectively (14.4% and 37.5% in average) when six controllers are used.

Compressionless Routing (GR) is a new adaptive routing framework which provides a unified framework for efficient deadlock-free adaptive routing and fault-tolerance. CR exploits the tight-coupling between wormhole routers for flow control to detect potential deadlock situations and recover from them. Fault-tolerant Compressionless Routing (FCR) extends Compressionless Routing to support end-to-end fault-tolerant delivery. Detailed routing algorithms, implementation complexity and performance simulation results for CR and FCR are presented.CR has the following advantages: deadlock-free adaptive routing in torus networks with no virtual channels, simple router designs, order-preserving message transmission, applicability to a wide variety of network topologies, and elimination of the need for buffer allocation messages. FCR has the following advantages: tolerates transient faults while maintaining data integrity (nonstop fault-tolerance), tolerates permanent faults, can be applied to a wide variety of network topologies, and eliminates the need for software buffering and retry for reliability. These advantages of CR and FCR not only simplify hardware support for adaptive routing and fault-tolerance, they also can simplify communication software layers.

The selection of a topology is essential to the performance of interconnection networks, so designing a new, cost-effective topology is very significant. 2D mesh is one of the most popular topologies. However, the diameter and average distance of a 2D mesh are large enough to greatly influence the performance of the network. This paper presents a novel topology called TM, which combines the advantages of both a 2D torus and a 2D mesh. For an n×n network, the total number of links in a TM is the same as that in a mesh, while the diameter of a TM is extremely close to that of a torus. Besides, the average distance of a TM is at the middle of that of a torus and that of a mesh. To prevent deadlocks in TMs, a virtual network partitioning scheme is adopted into the TM network. Moreover, both of the deterministic and fully-adaptive routing techniques in TMs are proposed in this paper. Compared to mesh, the TM network provides average distance and diameter reduction, which contributes to the performance enhancement. Sufficient simulation results are presented to show the effectiveness of the TM network, and the new routing schemes proposed for it, by comparing with the mesh network. Compared to the torus, which requires at least 3 virtual channels to support fully-adaptive routing, the TM network can support fully-adaptive routing with only 2 virtual channels. Seen from the experimental results, in most cases, the performance of TM is worse than the torus, while in some cases, the performance of TM is comparable to torus or even better than the torus.

We present a method to enhance wormhole routing algorithms for deadlock-free fault-tolerant routing in tori. We consider arbitrarily-located faulty blocks and assume only local knowledge of faults. Messages are routed via shortest paths when there are no faults, and this constraint is only slightly relaxed to facilitate routing in the presence of faults. The key concept we use is that, for each fault region, a fault ring consisting of fault free nodes and physical channels can be formed around it. These fault rings can be used to route messages around fault regions. We prove that at most four additional virtual channels are sufficient to make any fully-adaptive algorithm tolerant to multiple faulty blocks in torus networks. As an example of this technique, we present simulation results for a fully-adaptive algorithm and show that good performance can be obtained with as many as 10% links faulty.

Fault tolerant routing algorithms, are a key concern in on-chip communication. This paper examines fault tolerant communication algorithms for use in network-on-chip (NoC). We propose an improved wormhole-switched routing algorithm in 2-dimensional mesh based on f-cube3 algorithm to decrease message latency. The existing key concept is using numbers of virtual channels (VC) via a physical link. This paper proposes some improvements to make use of VCs while the numbers of them are fixed. We show that when a message is not blocked by fault, all VCs could be used; f-cube3, however, uses only one of the VCs. Furthermore, the strength of the improved algorithm is demonstrated by comparing results of simulations in both f-cube3 and the improved algorithm if-cube3.

A Hierarchical Torus Network (HTN) is a 2D-torus network of multiple basic modules, in which the basic modules are 3D-torus networks that are hierarchically interconnected for higher level networks. The dynamic communication performance of the HTN using the dimension-order routing under common traffic patterns have been evaluated, and have been shown to be good. However, dynamic communication performance of HTN under adverse traffic patterns has not been evaluated yet. In this paper, we evaluate the dynamic communication performance of HTN using a deadlock-free dimension order routing with 3 virtual channels under adverse traffic patterns, and compare it with H3D-mesh, mesh, and torus networks. It is shown that even under adverse traffic patterns, the HTN yields high throughput and low average transfer time, which provide better dynamic communication performance than H3D-mesh, mesh, and torus networks.

In this paper, we have evaluated the dynamic communication performance of the mesh and torus networks using a open source TOPAZ simulator using virtual cut through switching under uniform traffic pattern. It is found that the torus network yields low latency and high throughput than that of mesh network. Therefore, The dynamic communication performance of the torus network is better than that of the mesh network. The well known phenomenon is justified using a new open source simulator, TOPAZ simulator.

We present a fault tolerant method tailored for n-dimensional mesh networks that is able to handle multiple faults, even for two dimensional meshes. The method does not require existence of virtual channels. The traditional way of achieving fault tolerance based on adaptivity and adding virtual channels as the main mechanisms, has not shown the ability to handle multiple faults in wormhole mesh networks. In this paper we propose another strategy to provide high degree of fault-tolerance, we describe a technique which alters the routing function on the fly. The alteration action is always taken locally and distributed to a limited number of non-neighbor nodes.

The major concern in a Controller Area Network based safety critical system are node failures, its early detection and failure tolerance. Aiming at the improvement of node fault detection timing response and reliability of a CAN based distributed system, this paper mainly focuses on a new fault detection and tolerance algorithm named Distributed Node Fault Detection and Tolerance [DNFDT] Algorithm for Controller Area Network. The purpose of the algorithm is to have an effective fault detection method for (n-1) node faults for n node system by reducing the fault detection cycle timings and by limited checking on fault free nodes. A four node experimental hardware platform was implemented and performance evaluation of the time elapsed for one complete fault detection cycle under varying CAN bus loads have been obtained.

A new performance measure for characterizing fault rings in interconnection networks

Because of its excellent properties of fault tolerance, efficiency and availability, the practical Byzantine fault tolerance (PBFT) algorithm has become the mainstream consensus algorithm in blockchain. However, current PBFT algorithms have problems such as inadequate security of primary node selection, high communication overhead and network delay in the process of consensus. To address these problems, we design a novel efficient Byzantine fault tolerance algorithm based on credit grouping, called CG-PBFT. First, we propose a new credit evaluation model to obtain nodes’ credit values and introduce an optimized three-way quick sorting algorithm to divide nodes into the master-node group, the consensus-node group and the observation-node group, which have different privileges. The nodes in the observation-node group are restricted from participating in consensus, which reduces the communication overhead and improves consensus efficiency. Second, we propose an optimized selection method for the primary node based on a voting mechanism whereby the consensus-node group and observation-node group vote to produce the primary node, which reduces the probability of malicious nodes acting as the primary node and improves the security of primary node selection. Finally, the identity conversion mechanism between node groups is designed, and the actual behavior of nodes within different groups is given credit rewards or punishment, so as to keep an incentive for nodes to participate in appropriate system behavior and improve the working enthusiasm of nodes. The experimental simulation results show that compared with existing PBFT algorithms, the CG-PBFT algorithm improves the average throughput by 51.3% and reduces the average delay by 64.5%; it greatly improves the operating efficiency of the system and can be more suitable for application in the consortium blockchain scenarios.

The real-time intelligent perception and prediction of traffic situation can assist connected automated vehicles (CAVs) in path planning and reduce traffic congestion in Cognitive Internet of Vehicles (CIoVs). The centralized traffic congestion prediction solutions generally fail to adapt to the dynamic traffic environment and lead to significant communication overheads. Blockchain technology has attracted great attention in the information sharing of vehicular networks for its advantages in decentralization, transparency, traceability, and tamper-proof capability. However, due to the bottlenecks, such as high computational cost, current blockchains are incapable actuate on efficient online traffic situational cognition and prediction for CIoVs. Motivated by this, we propose a blockchain-enabled cognitive segments sharing framework for online multistep congestion duration prediction. We design a cognitive model of traffic situation based on anomaly detection and filtering mechanism to guarantee the accuracy of the cognitive segments before being packaged into the block. Furthermore, to improve the consensus efficiency, we design a credit evaluation mechanism and propose a credit-based delegated Byzantine fault tolerance (CDBFT) algorithm. Finally, we propose an online multistep prediction algorithm based on long short-term memory (LSTM) to predict future traffic congestion duration. Experimental results demonstrate that the proposed algorithms achieve shorter consensus latency and higher predictive accuracy than the existing algorithms.

Cloud computing is a promising paradigm that provides users higher computation advantages in terms of cost, flexibility, and availability. Nevertheless, with potentially thousands of connected machines, faults become more frequent. Consequently, fault-tolerant load balancing becomes necessary in order to optimize resources utilization while ensuring the reliability of the system. Common fault tolerance techniques in cloud computing have been proposed in the literature. However, they suffer from several shortcomings: some fault tolerance techniques use checkpoint-recovery which increases the average waiting time and thus the mean response time. While other models rely on task replication which reduces the cloud's efficiency in terms of resource utilization under variable loads. To address these deficiencies, an efficient and adaptive fault tolerant algorithm for load balancing is proposed. Based on the CloudSim simulator, some series of test-bed scenarios are considered to assess the behavior of the proposed algorithm.