VBMAR: virtual network load balanced minimal adaptive routing

A new deadlock prevention scheme for nonminimal adaptive wormhole routing

Wormhole routing makes the communication latency insensitive of the network diameter and reduces the buffer size of each router. It has been widely adopted in many new generation distributed memory multiprocessor systems (DMMPs). The concept of virtual system is invented for deadlock-free routing design. Using a great deal of virtual channels is quite expensive to be implemented in practice and is not limitless. In this paper experimental results are given to evaluate the tradeoff between network congestion delay and throughput. Some results show that the congestion delay does not reduce visibly when the number of virtual channels is greater than that of internal channels by 2. A reasonable number of virtual channels can be derived from the results. A virtual networks system using only four virtual networks, two virtual channels in each direction, is presented. It shows that the minimum number of virtual networks to support a partially adaptive, minimal and deadlock free routing in k-ary n-cubes is just four. It uses only four virtual networks but can get a high degree of adaptiveness and high traffic capacity. Simulation results are presented to verify the performance.

The authors describe a simple adaptive routing scheme for datagram (connectionless) and virtual circuit (connection-oriented) transmission that relieves congestion resulting from nonuniform traffic patterns and network failures. The authors describe a fixed-routing algorithm for dedicated channel ShuffleNets. Based on the fixed routing algorithm, an adaptive routing scheme for datagram transmission is presented followed by performance results for uniform and nonuniform traffic patterns and fault tolerance. The adaptive routing of datagrams uses only the local queue size information available at the network interface units (NIUs) and redistributes the load as congestion develops. Since datagrams are individually routed through the network, they may not arrive at their destination in the order they were generated and may need to be resequenced. The authors compute an upper estimate on the resequencing buffer size for stream traffic. A virtual circuit version of the adaptive routing algorithm eliminates the need for resequencing buffers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive routing is widely regarded as a promising approach to improving interconnection network performance. Many designers of adaptive routing algorithms have used synthetic communication patterns, such as uniform and transpose traffic, to compare the performance of various adaptive routing algorithms with each other and with oblivious routing. These comparisons have shown that the average message latency is usually lower with adaptive routing. On the other hand, when a parallel program is executed on a multiprocessor the goal is to reduce the total execution time. We explain why improving the average message latency of a routing algorithm does not necessarily lead to a lower execution time for real applications. We support this observation by reporting simulation results for both adaptive and oblivious routing using communication derived from real applications. Specifically, we report the performance of various routing algorithms for directed acyclic graphs (DAGs) derived from the Cholesky factorization of sparse matrices. Our results show that there is little correlation between average message latency and the total execution time of a parallel program. Hence, average message latency does not seem to be a useful measure of the performance of a routing algorithm. This strongly suggests that current comparisons of routing algorithms do not provide a reliable indication of the performance improvements to be realized by executing programs on a multiprocessor with such a routing algorithm. We interpret these results and suggest several alternatives for further research.

The performance of interconnection networks can be improved drastically by using wormhole routing and virtual channel flow control. Adaptive routing strategies, which are superior to oblivious routing, supply a set of alternative output virtual channels associated with different physical links, when a message is routed. A selection function selects a free one from the set. In this paper, we have evaluated the performance of three adaptive wormhole routing algorithms with minimum paths in 3D mesh networks: Dynamic Routing proposed by Dally and Aoki, Negative Last routing developed by Glass and Ni based on their Turn Model and Full Dynamic Routing proposed by us based on Duato’s adaptive routing theory. Three different selection functions, namely Static, Random and Greedy have been compared.

Adaptive deadlock-free routing mechanisms are required to handle variable traffic patterns in dragonfly networks. However, distance-based deadlock avoidance mechanisms typically employed in Dragonflies increase the router cost and complexity as a function of the maximum allowed path length. This paper presents on-the-fly adaptive routing (OFAR), a routing/flow-control scheme that decouples the routing and the deadlock avoidance mechanisms. OFAR allows for in-transit adaptive routing with local and global misrouting, without imposing dependencies between virtual channels, and relying on a deadlock-free escape subnetwork to avoid deadlock. This model lowers latency, increases throughput, and adapts faster to transient traffic than previously proposed mechanisms. The low capacity of the escape subnetwork makes it prone to congestion. A simple congestion management mechanism based on injection restriction is considered to avoid such issues. Finally, reliability is considered by introducing mechanisms to find multiple edge-disjoint Hamiltonian rings embedded on the dragonfly, allowing to use multiple escape subnetworks.

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.

A theory for the design of deadlock-free adaptive routing algorithms for wormhole networks, proposed by the author (1991, 1993), supplies sufficient conditions for an adaptive routing algorithm to be deadlock-free, even when there are cyclic dependencies between channels. Also, two design methodologies were proposed. Multicast communication refers to the delivery of the same message from one source node to an arbitrary number of destination nodes. A tree-like routing scheme is not suitable for hardware-supported multicast in wormhole networks because it produces many headers for each message, drastically increasing the probability of a message being blocked. A path-based multicast routing model was proposed by Lin and Ni (1991) for multicomputers with 2D-mesh and hypercube topologies. In this model, messages are not replicated at intermediate nodes. This paper develops the theoretical background for the design of deadlock-free adaptive multicast routing algorithms. This theory is valid for wormhole networks using the path-based routing model. It is also valid when messages with a single destination and multiple destinations are mixed together. The new channel dependencies produced by messages with several destinations are studied. Also, two theorems are proposed, developing conditions to verify that an adaptive multicast routing algorithm is deadlock-free, even when there are cyclic dependencies between channels. As an example, the multicast routing algorithms of Lin and Ni are extended, so that they can take advantage of the alternative paths offered by the network.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We present a model for designing wormhole routing algorithms that are deadlock free, livelock free, minimal or nonminimal, and maximally adaptive. A unique feature of this model is that it is not based on adding physical or virtual channels to network topologies (though it can be applied to networks with extra channels). Instead, the model is based on analyzing the directions in which packets can turn in a network and the cycles that the turns can form. Prohibiting just enough turns to break all of the cycles produces routing algorithms that are deadlock free, livelock free, minimal or nonminimal, and maximally adaptive for the network. In this paper, we focus on the two most common network topologies for wormhole routing,n-dimensional mesh, just a quarter of the turns must be prohibited to prevent deadlock. The remaining three quarters of the turns permit partial adaptiveness in routing. Partially adaptive routing algorithms are described for 2D meshes,n-dimensional meshes,k-aryn-cubes, and hypercubes. Simulations of partially adaptive and nonadaptive routing algorithms for 2D meshes and hypercubes show that which algorithm has the lowest latencies and highest sustainable throughput depends on the pattern of message traffic. For nonuniform traffic, partially adaptive routing algorithms perform better than non-adaptive ones.

A new deadlock-free routing scheme for meshes is proposed based on a new virtual network partitioning scheme, called channel overlapping. Two virtual networks can share some common virtual channels based on the new virtual network partitioning scheme. The deadlock-free adaptive routing method is then extended to deadlock-free adaptive fault-tolerant routing in 3D meshes still with two virtual channels. A few faulty nodes can make a higher dimensional mesh unsafe for fault-tolerant routing methods based on the block fault model, where the whole system (n-dimensional space) forms a fault block. Planar safety information in meshes is proposed to guide fault-tolerant routing and classifies fault-free nodes inside 2D planes. Many nodes globally marked as unsafe in the whole system become locally enabled inside 2D planes. This fault-tolerant deadlock-free adaptive routing algorithm is also extended to the one in an n-dimensional meshes with two virtual channels. Extensive simulation results are presented and compared to previous methods.

In this paper, we present the performance analysis of bufferless slotted optical packet switching using non uniform traffic pattern. The mathematical analysis has been done to evaluate the packet loss rate and also compared with the existing uniform traffic pattern. In addition to this, we have also studied the performance of the non uniform traffic pattern with the uniform traffic pattern of various packet sizes. Under non-uniform traffic pattern, packet loss rate is very much reduced compared to the uniform traffic pattern and more number of packets has been transmitted for the same period of time.

Due to Low-Rate Wireless Personal Area Networks(LR-WPANs) is popularly used in Internet of Things (IOT) in recent years, Chiu and Wang proposed a linked list routing algorithm with wormhole mechanism, which includes the linked list network construction mechanism, the wormhole mechanism and the MODBUS extension instructions for data collection. There are still a lot of non-adaptive problems in that algorithm, such that network initialization problem, continuous nodes broken problem and node outliers problem. Those problems could make the whole network stay in unstable state when the special conditions bring out. In this paper, we proposed an adaptive linked-list routing algorithm with wormhole mechanism. By proposed the Lock-address mechanism fundamentally, we can make the stable chain scission, reset sequentially and cutting timer determination mechanism for broken nodes. In simulation, the performance of network initialization of adaptive linked-list routing algorithm with wormhole mechanism and flooding is compared and simulated by NS3 in this paper. The simulations results reveal that the initialization of adaptive linked-list routing algorithm with wormhole mechanism is more efficient than flooding when nodes are 5 meters apart and a matrix model of nodes number from 7*7 to 15*15.

Communication delay in hypercubes in the presence of bit-reversal traffic

We consider routing and wavelength assignment in wavelength-routed all-optical networks (WAN) with circuit switching. The conventional approaches to address this issue consider the two aspects of the problem disjointly by first finding a route from a predetermined set of candidate paths and then searching for an appropriate wavelength assignment. We adopt a more general approach in which we consider all paths between a source-destination (s-d) pair and incorporate network state information into the routing decision. This approach performs routing and wavelength assignment jointly and adaptively, and outperforms fixed routing techniques. We present adaptive routing and wavelength assignment algorithms and evaluate their blocking performance. We obtain an analytical technique to compute approximate blocking probabilities for networks employing fixed and alternate routing. The analysis can also accommodate networks with multiple fibers per link. The blocking performance of the proposed adaptive routing algorithms are compared along with their computational complexity.

In this paper, we present an adaptive fault-tolerant wormhole routing algorithm for hypercubes by using 4 virtual networks. Each node is identified to be in one of the four states: safe, ordinarily unsafe, strongly unsafe, and faulty. Based on the concept of unsafe nodes, we design a routing algorithm for hypercubes that can tolerate at least n-1 faulty nodes and can route a message via a path of length no more than the Hamming distance between the source and destination plus four. Previous algorithms which achieve the same fault tolerant ability need at least 5 virtual channels per physical channel. Simulation results show that our algorithm outperforms previous known results.