Obtaining the optimal configuration of high-radix Combined switches

High-radix switches reduce network cost and improve network performance, especially in large switch-based interconnection networks. However, there are some problems related to the integration scale to implement such switches in a single chip. An interesting alternative for building high-radix switches consists of combining several current smaller single-chip switches to obtain switches with a greater number of ports. A key design issue of this kind of high-radix switches is the internal switch configuration, specifically, the correspondence between the ports of these high-radix switches and the ports of their smaller internal single-chip switches. In this paper we use artificial intelligence and data mining techniques in order to obtain the optimal internal configuration of all the switches in the network of large supercomputers running parallel applications. Simulation results show that using the resultant switch configurations, it is possible to achieve similar performance as with single-chip switches with the same radix, which would be unfeasible with the current integration scale.     

Cost Comparison of Alternative Architectures for IP-over-Optical Core Networks

We explore alternative architectures to reduce cost of IP-over-optical core networks. We conducted a detailed cost study of three architectures. We start with a Baseline architecture that captures present mode of operations with future traffic projections and utilizes technologies such as Ethernet line-cards and OTN sub-wavelength switching. The next architecture, Streamlined, replaces the hub-and-spoke topology of Baseline with a flat topology and is also more judicious in its restoration design. Our detailed study shows significant cost savings for the Streamlined architecture compared to the Baseline. We reduce the cost further in our third proposed architecture: Ethernet enabled IP core consisting of OTN switches (with and without packet switching) and without any backbone routers or MPLS switches. Our results also demonstrate that we can achieve significant reduction in switching costs but reducing cost of transport remains a significant challenge. This paper is an extended version of our previous work published in (11th international conference on the design of reliable communication networks (DRCN), pp 227–234, 2015).     

Formalization and configuration methodology for high-radix combined switches

In large switch-based interconnection networks, increasing the switch radix results in a decrease in the total number of network components, and consequently the overall cost of the network can be significantly reduced. Moreover, high-radix switches are an attractive option to improve the network performance in terms of latency since hop count is also reduced. However, there are some difficulties related to integration scale to design such switches. In this paper we present and formalize an interesting alternative for building high-radix switches going beyond the integration scale bounds. The idea basically consists in combining several current smaller switches to obtain switches having greater number of ports. This strategy will remain valid as the scale of integration keeps evolving. Although simple, this strategy raises key design challenges in order to these high-radix switches achieve the best performance. The resultant internal structure of these switches becomes an important design decision, and an arbitrary selection may produce a significant performance degradation. For this reason, we also propose a general methodology to configure in an optimal way the internal switch structure and apply it to a particular case in order to show how it works. The resultant switch configurations are evaluated in order to show the real potential of our proposal.     

A flexible optical switch architecture for efficient transmission of optical bursts

In this paper, we propose a new optical switch architecture for optical WDM networks. Flexibility and efficiency in terms of controlling and utilizing optical power are key features of the architecture. The architecture uses switching components which have increased flexibility of how optical power received on an input port is managed when switching optical signals. Like the traditional optical switches, optical power can be directed towards one output port only. Further, unlike the traditional switches, on need basis, the power can be split on a desired sub-set of output ports, thus reducing power wastage on unwanted ports. Such split power can be directed fully towards a single output port as and when it is needed. This flexible and efficient power management makes the architecture a potential candidate for optical networks with its usage in several dimensions. The dimensions include (1) switching methods such as circuit level switching and bursty level switching, (2) network types such as core, metro, and access networks, (3) support for technologies such as Light-trails and Light-trees, and (4) support for functionalities such as survivability and multicasting with new features. Importantly, there is potential that the architecture enhances adaptability based on the needs, and it supports co-existence and seamless integration of different environments.In this paper, our focus is on investigating bursty level switching using the proposed switch architecture. We use the flexibility of the switch and adopt a new switching method for data bursts. This switching method is efficient for switching bursts while introducing new challenges. Unlike the traditional switching method, it switches bursts arriving on an input link with zero (or very small) time gaps to different output links in certain scenarios. Further, it also switches bursts from different input links to the same output link when they arrive with zero (or very small) time interval. Adopting such switching approaches has potential benefits in terms of delay-load performance and blocking performance. While the bursts are switched from the same input link to different output links in this approach, it creates some unwanted signals. We investigate scenarios in which the unwanted signals create any problems and this poses some challenges. To address such challenges, we develop a transmission protocol. We investigate the performance of our solutions using simulation studies and verify the two significant gains: (1) networks’ capability to sustain traffic loads up to the maximum level in terms of the delay-load performance, which is similar to the performance seen for hypothetical ideal switches with zero switching time, and (2) improved blocking performance.     

Multicast support in multi-chip centralized schedulers in Input Queued switches

IQ switches store packets at input ports to avoid the memory speedup required by OQ switches. However, packet schedulers are needed to determine an I/O (input/output) interconnection pattern that avoids conflicts among packets at output ports. Today, centralized, single-chip, scheduler implementation are largely dominant. In the near future, the multi-chip scheduler implementation will be needed to reduce the hardware scheduler complexity in very large, high-speed, switches. However, the multi-chip implementation implies introducing a non-negligible delay among input and output selectors used to determine the I/O interconnection pattern at each time slot. This delay, mainly due to inter-chip latency, requires modifications to traditional scheduling algorithms, which normally rely on the hypothesis that information exchange among selectors can be performed with negligible delay. We propose a novel multicast scheduler, named IMRR, an extension of a previously proposed multicast scheduling algorithm named mRRM, making it suitable to a multi-chip implementation, and examine its performance by simulation.     

Cost-Efficient Dragonfly Topology for Large-Scale Systems

It is more efficient to use increasing pin bandwidth by creating high-radix routers with a large number of narrow ports instead of low-radix routers with fewer wide ports. Building networks using high-radix routers lowers cost and improves performance, but also presents many challenges. The dragonfly topology minimizes network cost by reducing the number of global channels required.     

Shortcut Switching Strategy in Metro Ethernet networks

IEEE Spanning Tree Protocol (STP) is a layer-2 protocol which provides a loop-free connectivity across various network nodes. STP does this task by reducing the topology of a switched network to a tree topology where redundant ports are blocked. Blocked ports are then kept in a standby mode of operation until a network failure occurs. In STP, there is not any traffic engineering mechanism for load balancing. This results in uneven load distribution and bottlenecks especially close to the Root. This protocol imposes a severe penalty on the performance and scalability of Metro Ethernet networks, since it makes inefficient use of links and switches. In this paper, we propose a novel switching strategy named Shortcut Switching Strategy (SSS) that uses blocked ports to forward frames in some special and restricted cases. It is an improved version of the standard STP and its main advantages are simplicity and backward-compatibility. Shortcut Switching Strategy decreases the average traffic volume on links and switches, improves load balancing on links and switches and reduces the Bandwidth Blocking Probability. We will demonstrate these improvements by using analytical and simulation methods for some well-known topologies. Simulation results show that using SSS can give about 25% reduction in average link loads, average switch loads and average number of hop counts compared to STP.     

Taking a free ride for routing topology inference in peer-to-peer networks

A Peer-to-Peer (P2P) network can boost its performance if peers are provided with underlying network-layer routing topology. The task of inferring the network-layer routing topology and link performance from an end host to a set of other hosts is termed as network tomography, and it normally requires host computers to send probing messages. We design a passive network tomography method that does not require any probing messages and takes a free ride over data flows in P2P networks. It infers routing topology based on end-to-end delay correlation estimation (DCE) without requiring any synchronization or cooperation from the intermediate routers. We implement and test our method in the real world Internet environment and achieved the accuracy of 92 % in topology recovery. We also perform extensive simulation in OMNeT++ to evaluate its performance over large scale networks, showing that its topology recovery accuracy is about 95 % for large networks.     

Linear recursive networks and their applications in distributedsystems

We present a new class of interconnection topologies called the Linear Recursive Networks (LRNs) and examine their possible applications in distributed systems. Each LRN is characterized by a recursive pattern of interconnection which can be specified by simple parameters. Basic properties such as node degree, diameter, and the performance of routing algorithms for all LRNs are then collectively analyzed in terms of these parameters. By choosing appropriate values for the parameters, our results can assist a network designer in selecting a topology with required routing performance and cost of interconnection. A subclass of LRNs, called Congruent LRNs (CLRNs), is also identified here and shown to possess desirable properties for more tightly coupled systems. It is shown that the CLRNs include existing networks such as hypercube and generalized Fibonacci cubes. These results suggest that the linear recursive networks potentially have applications in interconnecting distributed systems     

Chams: Churn-aware overlay construction for media streaming

Overlay networks support a wide range of peer-to-peer media streaming applications on the Internet. The user experience of such applications is affected by the churn resilience of the system. When peers disconnect from the system, streamed data may be delayed or lost due to missing links in the overlay topology. In this paper, we explore a proactive strategy to create churn-aware overlay networks that reduce the potential of disruptions caused by churn events. We describe Chams, a middleware for constructing overlay networks that mitigates the impact of churn. Chams uses a ??hybrid?? approach??it implicitly defines an overlay topology using a gossip-style mechanism, while taking the reliability of peers into account. Unlike systems for overlay construction, Chams supports a variety of topologies used in media streaming systems, such as trees, multi-trees and forests. We evaluate Chams with different topologies and show that it reduces the impact of churn, while imposing only low computational and message overheads.     

Location and Configuration Management in Mobile-Switch ATM Networks

The features of two important application scenarios, supporting mobile switches with fixed end users and mobile switches with mobile users, are dramatically different from those of the traditional wired network structure. To exploit mobile switches, the location and configuration management of mobile switches is essential to handle the mobility and topology change of the wireless/mobile ATM network. In this paper we address the location management and configuration problems of mobile switches in an ATM network. We investigate several aspects of the location management problem including architecture to support switch mobility, mobile switch tracking, and mobile switch locating. We propose an approach that is based on the Private Network-Network Interface (PNNI) protocol. We extend the PNNI protocol to enable it to handle mobile switches. Moreover, we develop analytical models to determine the tracking and locating costs for mobile switches under the proposed scheme. The models illustrate the relation between total cost (tracking cost + locating cost) and peer group size. The models can be used to derive the optimal configuration for an ATM network with mobile switches.     

Epidemic-based reliable and adaptive multicast for mobile ad hoc networks

An emerging approach to distributed systems exploits the self-organization, autonomy and robustness of biological epidemics. In this article, we propose a novel bio-inspired protocol: EraMobile (Epidemic-based Reliable and Adaptive Multicast for Mobile ad hoc networks). We also present extensive performance analysis results for it. EraMobile supports group applications that require high reliability. The protocol aims to deliver multicast data reliably with minimal network overhead, even under adverse network conditions. With an epidemic-based multicast method, it copes with dynamic and unpredictable topology changes due to mobility. Our epidemic mechanism does not require maintaining any tree- or mesh-like structure for multicasting. It requires neither a global nor a partial view of the network, nor does it require information about neighboring nodes and group members. In addition, it substantially lowers overhead by eliminating redundant data transmissions. Another distinguishing feature is its ability to adapt to varying node densities. This lets it deliver data reliably in both sparse networks (where network connectivity is prone to interruptions) and dense networks (where congestion is likely). We describe the working principles of the protocol and study its performance through comparative and extensive simulations in the ns-2 network simulator.     

基于端口流量的物理网络拓扑发现方法研究

物理网络拓扑从第二层反映出交换机之间的连接关系,它在网络管理系统中具有重要的地位。文章通过对交换机端口流量的分析,提出在交换式以太网中利用端口流量进行物理网络拓扑发现的方法,即端口流量法。该方法适用于多数交换式以太网环境,在实验环境中较好地发现物理网络拓扑。     

Design and performance of speculative flow control for high-radix datacenter interconnect switches

High-radix switches are desirable building blocks for large computer interconnection networks, because they are more suitable to convert chip I/O bandwidth into low latency and low cost than low-radix switches [J. Kim, W.J. Dally, B. Towles, A.K. Gupta, Microarchitecture of a high-radix router, in: Proc. ISCA 2005, Madison, WI, 2005]. Unfortunately, most existing switch architectures do not scale well to a large number of ports, for example, the complexity of the buffered crossbar architecture scales quadratically with the number of ports. Compounded with support for long round-trip times and many virtual channels, the overall buffer requirements limit the feasibility of such switches to modest port counts. Compromising on the buffer sizing leads to a drastic increase in latency and reduction in throughput, as long as traditional credit flow control is employed at the link level. We propose a novel link-level flow control protocol that enables high-performance scalable switches that are based on the increasingly popular buffered crossbar architecture, to scale to higher port counts without sacrificing performance. By combining credited and speculative transmission, this scheme achieves reliable delivery, low latency, and high throughput, even with crosspoint buffers that are significantly smaller than the round-trip time. The proposed scheme substantially reduces message latency and improves throughput of partially buffered crossbar switches loaded with synthetic uniform and non-uniform bursty traffic. Moreover, simulations replaying traces of several typical MPI applications demonstrate communication speedup factors of 2 to 10 times.     

Topological network design: A survey

We consider the problem of topological optimization of communication networks subject to a number of design constraints, such as maximum network diameter, maximum node degree, k-node (link) survivability, and network fault tolerance. The primary design problem can be described as follows: Given a set of network nodes, it is required to find a topology Ψ, selected from all possible topologies, so that the cost of Ψ (measured possibly in terms of the maximum diameter, maximum node degree, etc.) is less than that of any other network topology and such that Ψ satisfies some given design constraints. Fault tolerance is concerned with the ability of the network nodes to communicate in the presence of a set of faulty links and/or nodes. The network design problem considering reliability constraints is NP-hard. We classify the research efforts presented in the literature for solving the topological optimization design problem as hierarchical, enumerative, or iterative techniques. In this paper, we provide a survey of the topological network design techniques under different design constraints. Experimental results obtained by applying a number of algorithms to a set of randomly generated networks are presented and compared.     

An update-based step-wise optimal cache replacement for wireless data access

Many network applications requires access to most up-to-date information. An update event makes the corresponding cached data item obsolete, and cache hits due to obsolete data items become simply useless to those applications. Frequently accessed but infrequently updated data items should get higher preference while caching, and infrequently accessed but frequently updated items should have lower preference. Such items may not be cached at all or should be evicted from the cache to accommodate items with higher preference. In wireless networks, remote data access is typically more expensive than in wired networks. Hence, an efficient caching scheme considers both data access and update patterns can better reduce data transmissions in wireless networks. In this paper, we propose a step-wise optimal update-based replacement policy, called the Update-based Step-wise Optimal (USO) policy, for wireless data networks to optimize transmission cost by increasing effective hit ratio. Our cache replacement policy is based on the idea of giving preference to frequently accessed but infrequently updated data, and is supported by an analytical model with quantitative analysis. We also present results from our extensive simulations. We demonstrate that (1) the analytical model is validated by the simulation results and (2) the proposed scheme outperforms the Least Frequently Used (LFU) scheme in terms of effective hit ratio and communication cost.     

基于InfiniBand的多链路mesh/torus大规模并行系统互连网络

在大规模并行系统中,系统级互连网络的设计至关重要.InfiniBand作为一种高性能交换式网络被广泛应用于大规模并行处理系统中.mesh/torus拓扑结构相较于目前普遍应用于InfiniBand网络的胖树拓扑结构拥有更好的性能与可扩展性.尽管如此,研究发现,用传统的mesh/torus拓扑结构构建InfiniBand互连网络存在诸多问题.分析了传统网络拓扑结构的缺陷,并提出了一种基于InfiniBand的多链路mesh/torus互连网络.这种改进型的拓扑结构通过充分利用交换机间的多链路可以获得比传统mesh/torus网络更高的带宽.另外,同时给出了与该网络拓扑结构相配套的高效路由算法.最后,通过网络仿真技术对提出的算法进行了评估,实验结果显示提出的路由算法相较于其他路由算法拥有更好的性能与可扩展性.     

Adaptive-trail routing and performance evaluation in irregularnetworks using cut-through switches

Cut-through switching promises low latency delivery and has been used in new generation switches, especially in high speed networks demanding low communication latency. The interconnection of cut-through switches provides an excellent network platform for high speed local area networks (LANs). For cost and performance reasons. Irregular topologies should be supported in such a switch-based network. Switched irregular networks are truly incrementally scalable and have potential to be reconfigured to adapt to the dynamics of network traffic conditions. Due to the arbitrary topologies of networks, it is critical to develop an efficient deadlock-free routing algorithm. A novel deadlock-free adaptive routing algorithm called adaptive-trail routing is proposed to allow irregular interconnection of cut-through switches. The adaptive routing algorithm is based on two unidirectional adaptive trails constructed from two opposite unidirectional Eulerian trails. Some heuristics are suggested in terms of the selection of Eulerian trails, the avoidance of long routing paths, and the degree of adaptivity. Extensive simulation experiments are conducted to evaluate the performance of the proposed and two other routing algorithms under different topologies and traffic workloads     

On Minimizing the Cost of Location Management in Mobile Environments

A mobile host typically has a home agent that maintains a registry of its current location. This registry is normally updated every time a host changes its current network. The update cost could be reduced using a two-tier update process in which a registry is updated using special agents, called proxy agents. We study the problem of selecting proxy agents to minimize the cost of search associated with this two-tier update approach. We show that the problem can be formulated as p-center or p-median finding problems. We focus on the p-center formulation. Due to the intractability of the problem, we introduce a distributed strategy to solve the general problem and show that it yields an approximate solution for arbitrary networks. We present an implementation of the distributed strategy that produces an optimal solution for ring networks. We prove that the optimal solution for rings is fault tolerant and resilient to topology changes.     

Performance analysis of small non-uniform packet switches

Packet switches have been studied extensively as part of ATM and LAN networks under the assumption that the number of input ports N tends to infinity. Our study of packet switches is motivated by networks on chips, where N is usually 4 or 5 and asymptotic models lead to inaccurate results. We consider small non-uniform switches and accurately approximate stability conditions and throughput. In addition to this, we approximate the mean waiting time in the switch by that in a ./Geo/1 queue.