Enhanced fault tolerant routing algorithms using a concept of “balanced ring”

Fault rings can be used to guide messages bypass faulty nodes/links in a fault tolerant interconnection network. However, nodes on the fault ring become hot spots, thus causing uneven distribution of the traffic loads. To avoid such traffic congestion, a concept of the balanced ring is proposed in this paper. The proposed balanced ring, defined as concentric rings of a given fault ring, can be applied to the fault tolerant routing algorithms for mesh and torus topologies. By properly guiding messages to route on the balanced ring and the fault ring, more balanced link utilization and greatly reduced traffic congestion can be achieved on a fault tolerant network. Methods of applying the balanced ring concept to some published fault tolerant routing algorithms are discussed. Proof of deadlock and livelock freedom is also presented. The use of balanced ring does not need to add new virtual channels. The performance of two routing algorithms with and without the balanced ring is simulated and evaluated. The results indicate that routing algorithms with the balanced rings constantly yield larger throughput and smaller latency than those without.     

A family of mechanisms for congestion control in wormhole networks

Multiprocessor interconnection networks may reach congestion with high traffic loads, which prevents reaching the wished performance. Unfortunately, many of the mechanisms proposed in the literature for congestion control either suffer from a lack of robustness, being unable to work properly with different traffic patterns or message lengths, or detect congestion relying on global information that wastes some network bandwidth. This paper presents a family of mechanisms to avoid network congestion in wormhole networks. All of them need only local information, applying message throttling when it is required. The proposed mechanisms use different strategies to detect network congestion and also apply different corrective actions. The mechanisms are evaluated and compared for several network loads and topologies, noticeably improving network performance with high loads but without penalizing network behavior for low and medium traffic rates, where no congestion control is required.     

Fuzzy-based Adaptive Routing Algorithm for Networks-on-Chip

In this paper, we propose two adaptive routing algorithms to alleviate congestion in the network. In the first algorithm, the routing decision is assisted by the number of occupied buffer slots at the corresponding input buffer of the next router and the congestion level of that router. Although this algorithm performs better than the conventional method, DyXY, in some cases the proposed algorithm leads to non-optimal decisions. Fuzzy controllers compensate for ambiguities in the data by giving a level of confidence rather than declaring the data simply true or false. To make a better routing decision, we propose an adaptive routing algorithm based on fuzzy logic for Networks-on-chip where the routing path is determined based on the current condition of the network. The proposed algorithm avoids congestion by distributing traffic over the routers that are less congested or have a spare capacity. The output of the fuzzy controller is the congestion level, so that at each router, the neighboring router with the lowest congestion value is chosen for routing a packet. To evaluate the proposed routing method, we use two multimedia applications and two synthetic traffic profiles. The experimental results show that the fuzzy-based routing scheme improves the performance over the DyXY routing algorithm by up to 25% with a negligible hardware overhead.     

一种MPLS流量工程中的动态路由算法

提出了一种MPLS流量工程中新的保证带宽的动态路由算法。传统的算法如SPF(Shortest Path First)算法、WSP算法（Widest Shortest Path）等都没有利用业务分布或入出路由器对（Ingress-Egress Pairs）的信息,可能导致严重的网络资源使用不充分的问题。该方法分两步：①离线路由,基于业务分布和日常统计的静态研究;该阶段能充分利用网络资源,有助于在线路由阶段动态路径的选择及避免拥塞;②根据第①步的结论及实际的网络状态,在线路由。重点针对在线路由提出了一种新的动     

Vehicle routing under time-dependent travel times: The impact of congestion avoidance

Daily traffic congestion forms a major problem for businesses such as logistic service providers and distribution firms. It causes late arrivals at customers and additional costs for hiring the truck drivers. Such costs caused by traffic congestion can be reduced by taking into account and avoiding predictable traffic congestion within vehicle route plans. In the literature, various strategies are proposed to avoid traffic congestion, such as selecting alternative routes, changing the customer visit sequences, and changing the vehicle-customer assignments. We investigate the impact of these and other strategies in off-line vehicle routing on the performance of vehicle route plans in reality. For this purpose, we develop a set of vehicle routing problem instances on real road networks, and a speed model that reflects the key elements of peak hour traffic congestion. The instances are solved for different levels of congestion avoidance using a modified Dijkstra algorithm and a restricted dynamic programming heuristic. Computational experiments show that 99% of late arrivals at customers can be eliminated if traffic congestion is accounted for off-line. On top of that, about 87% of the extra duty time caused by traffic congestion can be eliminated by clever congestion avoidance strategies.     

Deadlock-free multicast wormhole routing in 2-D mesh multicomputers

Multicast communication services, in which the same message is delivered from a source node to an arbitrary number of destination nodes, are being provided in new-generation multicomputers. Broadcast is a special case of multicast in which a message is delivered to all nodes in the network. The nCUBE-2, a wormhole-routed hypercube multicomputer, provides hardware support for broadcast and a restricted form of multicast in which the destinations form a subcube. However, the broadcast routing algorithm adopted in the nCUBE-2 is not deadlock-free. In this paper, four multicast wormhole routing strategies for 2-D mesh multicomputers are proposed and studied. All of the algorithms are shown to be deadlock-free. These are the first deadlock-free multicast wormhole routing algorithms ever proposed. A simulation study has been conducted that compares the performance of these multicast algorithms under dynamic network traffic conditions in a 2-D mesh. The results indicate that a dual-path routing algorithm offers performance advantages over tree-based, multipath, and fixed-path algorithms     

基于改进Dijkstra算法的配用电通信网流量调度策略

针对配用电通信网中数据汇聚易产生拥塞的问题,提出了一种复合边权值流量调度路由算法。首先,依据跳数建立节点分层模型;然后,划分配用电业务优先级和节点拥塞等级;最后,以跳数、流量负载率和链路利用率为综合指标计算边权值,对需要流量调度的节点根据改进的Dijkstra算法进行路由选择,同时对重度拥塞节点按照配用电业务优先级进行调度。与最短路径（SPF）算法和贪婪背压算法（GBRA）相比,在数据生成率为80 kb/s时,所提算法紧急型业务丢包率分别减少了81.3%和67.7%,关键型业务丢包率分别减少了79%和63.8%。仿真结果表明,所提算法能有效缓解网络拥塞,提高网络有效吞吐量,降低网络端到端时延和高优先级业务的丢包率。     

Bi-LCQ: A low-weight clustering-based Q-learning approach for NoCs

Network congestion has a negative impact on the performance of on-chip networks due to the increased packet latency. Many congestion-aware routing algorithms have been developed to alleviate traffic congestion over the network. In this paper, we propose a congestion-aware routing algorithm based on the Q-learning approach for avoiding congested areas in the network. By using the learning method, local and global congestion information of the network is provided for each switch. This information can be dynamically updated, when a switch receives a packet. However, Q-learning approach suffers from high area overhead in NoCs due to the need for a large routing table in each switch. In order to reduce the area overhead, we also present a clustering approach that decreases the number of routing tables by the factor of 4. Results show that the proposed approach achieves a significant performance improvement over the traditional Q-learning, C-routing, DBAR and Dynamic XY algorithms.     

一种考虑节点拥塞情况的DTN概率路由算法*

容迟网络是一种新型网络,其概率路由算法根据历史相遇频率对相遇概率进行计算与更新,通过相遇概率判断是否转发报文。当节点缓存受限时,在网络中采用概率路由算法使得节点很容易发生拥塞,对报文的传送产生影响。为了减小拥塞对概率路由算法的影响,提出了一种考虑节点拥塞情况的概率路由算法,将节点相遇的概率和节点拥塞的情况综合起来,得到一个报文的递交概率,降低了由于拥塞对网络性能的影响,提高了报文的递交率,减小了报文在缓存中排队等候的时间。仿真结果表明,与传统的概率路由算法相比,在改进后的概率路由算法中报文递交率显著提高,平均延迟也在降低。     

Bio-inspired self-aware fault-tolerant routing protocol for network-on-chip architectures using Particle Swarm Optimization

This research paper proposes a bio-inspired self-aware fault-tolerant routing protocol for network-on-chip architecture using particle swarm optimization (PSO), which considers synchronous, asynchronous, and self-organizing communication mechanisms to intelligently load-balance the traffic on the entire network in the presence of faulty components. By way of experimentation and simulation, this study demonstrates that the proposed scheme can converge to a global optimum, minimal routing path in real time, in the presence of network congestion and faulty routers and links. The basic PSO algorithm was improved to implement the proposed routing scheme, named bio-inspired self-aware fault-tolerant routing protocol (BISFTRP). This scheme uses the synchronous, asynchronous, and self-organizing features of PSO to create a global routing table and intelligent adaptation, which gives rise to scalable, real-time, and dynamic routing decisions with high throughput, low latency, and minimum power consumption. A cycle-accurate simulation system to demonstrate the flexibility and efficiency of the proposed scheme is used. Comparison results with state-of-the-art fault-tolerant routing algorithms show that the BISFTRP routing protocol achieves high routing performance without routing oscillations and throughput degradation. Furthermore, the hardware implementation results show that the BISFTRP router achieves an efficient area and power utilization, compared with state-of-the-art routers.     

Extension of Multiprotocol Label Switching for long-range dependent traffic: QoS routing and performance in IP networks

This paper presents an extension to the Multiprotocol Label Switching (MPLS) traffic engineering in IP networks with long-range dependent traffic. The extension provides the ability to diverge traffic flows away from the shortest path calculated by the traditional IP routing protocols into a less congested area of the network. When the traffic burstiness of a packet flow exceeds a predefined threshold, the extension calculates the cost of the traffic distribution and the effectiveness of Label Switching Routers (LSPs) to minimize the number of discarded packets. The simulation results demonstrate that the extension significantly improves the overall network performance in link utilization, port processor utilization, message delay, number of dropped packets, and buffer usage level.     

流量工程中多维目标优化的路由算法综述

互联网中传统的最短路径路由算法本质上存在导致拥塞的可能。网络拥塞不仅会降低网络性能,而且会使得服务提供商难以完成对客户的服务质量保证。通过在路由选择阶段面向流量工程实施优化,能够避免拥塞,提高网络资源利用率。概述面向流量工程的约束路由算法的研究进展。首先阐述了三类主要的流量工程优化目标：最小化网络资源占用、负载平衡和最小干涉,然后分析了各类典型算法,最后对此方向的研究进行了总结和展望。     

A new congestion control algorithm for improving the performance of a broadcast-based multiprocessor architecture

Congestion occurring in the input queues of broadcast-based multiprocessor architectures can severely limit their overall performance. The existing congestion control algorithms estimate congestion based on a node’s output channel parameters such as the number of free virtual channels or the number of packets waiting at the channel queue. In this paper, we have proposed a new congestion control algorithm to prevent congestion on broadcast-based multiprocessor architectures with multiple input queues. Our algorithm performs congestion control at the packet level and takes into account the next input queue number which will be accessed by the processor, which form the fundamental differences between our algorithm and the algorithms based on the idea of virtual channel congestion control. The performance of the algorithm is evaluated by OPNET Modeler with various synthetic traffic patterns on a 64-node Simultaneous Optical Multiprocessor Exchange Bus (SOME-Bus) architecture employing the message passing protocol. Performance measures such as average input waiting time, average network response time and average processor utilization have been collected before and after applying the algorithm. The results show that the proposed algorithm is able to decrease the average input waiting time by 13.99% to 20.39%, average network response time by 8.76% to 20.36% and increase average processor utilization by 1.92% to 6.63%. The performance of the algorithm is compared with that of the other congestion control algorithms and it is observed that our algorithm performs better under all traffic patterns. Also, theoretical analysis of the proposed method is carried out by using queuing networks.     

Performance evaluation of mesh-based NoCs: Implementation of a new architecture and routing algorithm

This paper presents the result of experiments conducted in mesh networks on different routing algorithms, traffic generation schemes and switching schemes. A new network on chip (NoC) topology based on partial interconnection of mesh network is proposed and a routing algorithm supporting the proposed architecture is developed. The proposed architecture is similar to standard mesh networks, where four extra bidirectional channels are added which remove the congestion and hotspots compared to standard mesh networks with fewer channels. Significant improvement in delay (60% reduction) and throughput (60% increase) was observed using the proposed network and routing when compared with the ideal mesh networks. An increase in number of channels makes the switches expensive and could increase the area and power consumption. However, the proposed network can be useful in high speed applications with some compromise on area and power.     

Reconfigurable multicast routing for Networks on Chip

Several unicast and multicast routing protocols have been presented for MPSoCs. Multicast protocols in NoCs are used for cache coherency in distributed shared memory systems, replication, barrier synchronization, or clock synchronization. Unicast routing algorithms are not suitable for multicast, as they increase traffic, congestion and deadlock probability. Famous multicast schemes such as tree-based and path-based schemes have been proposed originally for multicomputers and recently adapted to NoCs. In this paper, we propose a switch tree-based multicast scheme, called STBA. This method supports tree construction with a minimum number of routers. Our evaluation results reveal that, for both synthetic and real traffic loads, the proposed scheme outperforms the baseline tree-based routing scheme in a conventional mesh by up to 41% and reduces power consumption by up to 29%.     

基于全分布式分组无线网络的蚂蚁路由算法

该文介绍了全分布式分组无线网络中路由算法。当前广泛运用的OSPF路由算法在网络的链路发生阻塞时，不能及时探测到链路状况。当链路发生拥塞时，在发包率继续增大的时候，只能简单地丢弃数据包。就此该文在分布式的无线网络中应用了蚂蚁算法。该算法由发送探测包来担任“觅食蚂蚁”在短时间内找出最优路径，分散流量，避免网络的拥塞。通过仿真结果表明：该算法在网络利用率和数据包传送时延上有较好的改善。     

A general methodology for direction-based irregular routing algorithms

This paper presents a general methodology for generating deadlock-free routing algorithms for irregular networks. Constructing a spanning tree on the given network, assigning directions to the network channels, creating deadlock-free zones, and specifying a logical sequence of the produced deadlock-free zones are the four fundamental steps that the proposed methodology takes to generate deadlock-free and connected routing algorithms. By applying the proposed methodology with two known labeling methods we have generated six irregular routing algorithms: three of them are novel routing algorithms and three of them (the Up/Down, Left/Right, and L-turn routing algorithms) have already been proposed in the literature. Extensive simulation experiments have been performed considering various network topologies, different network sizes (considering different network nodes and network channels), various message lengths, a variety of spanning tree roots, and a wide range of message (traffic) generation rates. Simulation results show that the six routing algorithms can be divided into three pairs. Routing members of each pair show similar behavior in terms of message latencies and saturation generation rates. However, it is worth noting that for a given topology the performance of the six routing algorithms may be totally different and it mainly depends on the network topology.     

A new performance measure for characterizing fault rings in interconnection networks

One of the fundamental issues in parallel computers is how to efficiently perform routing in a faulty network where each component fails with some probability. Adaptive fault-tolerant routing algorithms in such systems have been frequently suggested as a means of providing continuous operations in the presence of one or more failures by allowing the graceful system degradation. Many algorithms involve adding buffer space and complex control logic to the routing nodes. However, the addition of extra logic circuits and buffer space makes nodes more liable to failure and less reliable. Further, if the shape of fault pattern is confined, then many non-faulty nodes will be sacrificed and hence their resources are wasted. This is clearly an undesirable solution and motivates solutions that provoke efficient use of non-faulty nodes. One such approach to reducing the number of functional nodes that must be marked as faulty is based on the concept of fault rings to support more flexible routing around rectangular fault regions. Before such schemes can be successfully incorporated in networks, it is necessary to have a clear understanding of the factors that affect their performance potential. In this paper, we propose the first general solution for computing the probability of message facing the fault rings with and without overlapping in the well-known torus networks. We also conduct extensive simulation experiments using various fault patterns, the results of which are used to confirm the good accuracy of the proposed analytical models.     

ERC2:具有拥塞控制策略的DTN传染路由方法

针对延迟容忍网络（DTN）拓扑结构动态变化和节点存储空间有限的问题,提出一种具有拥塞控制策略的DTN传染路由（ERC²）方法。该方法基于一种动态存储状态模型（DSSM）,节点可通过感知网络状况动态调整节点半拥塞状态的门限降低网络发生拥塞的可能性,增加ACK索引以及消息管理队列,使节点存储状态随着网络负载的随机变化而动态更新并主动删除冗余包,并根据不同拥塞状态结合传染路由和Prophet路由的优点选择单一或混合模式进行消息转发,从而达到预防、避免、解除拥塞的目的,实现节点自适应缓存管理以及网络的动态拥塞控制。在模拟器ONE上采用Working Day Movement模型进行仿真,其中与Prophet相比,ERC²方法在消息递交率上提高66.18%,平均时延降低48.36%,转发次数提高22.83%。仿真结果表明,在拥塞程度不同的场景中,ERC²与Epidemic、Prophet路由算法相比具有更好的网络性能。     

小时间尺度网络拥塞研究*

基于窗口的拥塞控制算法通常忽略了比往返时间级更小的时间尺度上的网络拥塞,因此不能达到设计的预期效果。重点从理论上研究了窗口更新算法与小时间尺度网络拥塞之间的相互关系,提出了窗口递增算法的小时间尺度突发性度量方法,并分析了小缓冲高速网络环境下传统TCP窗口递增算法的效率。