Performance modeling of Cartesian product networks

This paper presents a comprehensive performance model for fully adaptive routing in wormhole-switched Cartesian product networks. Besides the generality of the model which makes it suitable to be used for any product graph, experimental (simulation) results show that the proposed model exhibits high accuracy even in heavy traffic and saturation region, where other models have severe problems to predict the performance of the network. Most popular interconnection network can be defined as a Cartesian product of two or more networks including the mesh, hypercube, and torus networks. Torus and mesh networks are the most popular topologies used in recent supercomputing parallel machines. They have been widely used for realizing on-chip network in recent on-chip multicore and multiprocessors system.     

Performance improvement of dynamic buffered ATM switch

Performance of ATM networks depends on switch performance and architecture. This paper presents a simulation study of a new dynamic allocation of input buffer space in ATM switching elements. The switching elements are composed of input and output buffers which are used to store received and forwarded cells, respectively. Efficient and fair use of buffer space in an ATM switch is essential to gain high throughput and low cell loss performance from the network. In this paper, input buffer space of each switching element is allocated dynamically as a function of traffic load. A shared buffer pool is provided with threshold-based virtual partition among input ports, which supplies the necessary input buffer space as required by each input port. The system behaviour under varying traffic loads has investigated using a simulation program. Also, a comparison with a static allocation scheme shows that the threshold based dynamic buffer allocation scheme ensures an increased network throughput and a fair share of the buffer space even under bursty loading conditions.     

Approximate analysis of a discrete-time tandem network of cut-through queues with blocking and bursty traffic

A discrete-time tandem network of cut-through queues is presented. The model allows finite capacity queues, blocking, and bursty traffic. A new bursty arrival process, IBK(k), for cut-through traffic is introduced. The tandem network is analyzed using single-node decomposition. Each queue is analyzed numerically in isolation assuming that its arrival and service processes are known. The parameters of the arrival and service processes of the queues are obtained using an iterative scheme. The results obtained are approximate and validation tests have shown that the model has good accuracy. Using this model, the packet loss, throughput, and queue length distributions were obtained for different traffic parameters and queue sizes.     

Performance estimation of banyan semi layer networks with drop resolution mechanism

Multistage interconnection networks (MINs) are a basic class of switch-based network architectures, which are used for constructing scalable parallel computers or for connecting networks. Semi-layer MINs are a special case of MINs. A performance evaluation of semi-layer MINs (using simulation models) is presented in this paper. The configurations of the under study networks apply a conflict drop resolution mechanism. The proposed architecture's performance is studied under uniform traffic conditions and various offered loads, buffer-lengths and MIN sizes. In this paper, the improvements on semi-layer MIN performance, in terms of throughput and latency, are demonstrated quantitatively. These performance measures can be valuable tools for designers of parallel multiprocessor systems and networks, in order to minimize the overall deployment costs and help deliver efficient systems.     

Analysis of a finite buffer queue with different scheduling and push-out schemes

A queueing system M₁, M₂/G₁, G₂/1/N with different scheduling and push-out scheme is analyzed in this paper. This work is motivated by the study of the performance of an output link of ATM switches with traffic of two classes with different priorities. However, the queueing model developed in this paper is more general than that of the output link of ATM switches with two-class priority traffic. General service time distributions are allowed for classes 1 and 2 and a general service discipline function, ₁(i, j), is introduced where ₁(i, j) is the probability that a class 1 packet will be served, given that there are i class 1 and j class 2 packets waiting for service. An exact solution is obtained for the loss probabilities for classes 1 and 2, the queue length distribution and the mean waiting time for class 1. The queue length distribution and the mean waiting time for class 2 are calculated approximately. It is shown that the approximation is an upper bound and the error due to the approximation is very small when the loss probability of class 2 is small (e.g., less than 0.01).     

Performance of GSM networks with general packet radio services

Recently, most of the mobile network providers start to introduce general packet radio service (GPRS) in their existing GSM networks. GPRS is the technology that will enable more efficient Internet applications to run on mobile networks even before the installation of 3G systems. However, it is not yet clearly understood, how the new data services will affect the overall network performance. This paper provides a framework for analytical performance evaluation of a single GSM/GPRS cell based on a multidimensional Markov chain model. Important performance measures like new call and handover blocking probabilities, moments of the blocking period distributions, achievable average data rates and resource utilization are determined. Introducing a new connection admission control (CAC) algorithm, different partitioning strategies between GSM and GPRS resources are investigated. Finally, the influence of typical GPRS applications like Internet browsing on traditional GSM services has been studied.     

Infinitesimal and finite perturbation analysis for queueing networks

The sample-path perturbation analysis technique is extended to include finite (and possibly large) perturbations typically introduced by changes in queue sizes or other parameters. It is shown that there is a natural hierarchy of perturbation analysis which takes care of increasingly large perturbations. Experiments with zero (infinitesimal) and first order (finite) perturbation analysis show that significant accuracy improvement can be obtained with small increase in computational effort.     

Characterization of spatial fault patterns in interconnection networks

Parallel computers, such as multiprocessors system-on-chip (Mp-SoCs), multicomputers and cluster computers, are consisting of hundreds or thousands multiple processing units and components (such as routers, channels and connectors) connected via some interconnection network that collectively may undergo high failure rates. Therefore, these systems are required to be equipped with fault-tolerant mechanisms to ensure that the system will keep running in a degraded mode. Normally, the faulty components are coalesced into fault regions, which are classified into two major categories: convex and concave regions. In this paper, we propose the first solution to calculate the probability of occurrences of common fault patterns in torus and mesh interconnection networks which includes both convex (-shaped, □-shaped) and concave (L-shaped, T-shaped, +-shaped, H-shaped) regions. These results play a key role when studying, particularly, the performance analysis of routing algorithms proposed for interconnection networks under faulty conditions.     

Performance modeling and analysis of heterogeneous meta-computing systems interconnection networks

The overall performance of a distributed system often depends on the effectiveness of its interconnection network. Thus, the study of the communication networks for distributed systems is very important, which is the focus of this paper. In particular, we address the problem of interconnection networks performance modeling for heterogeneous meta-computing systems. We consider the meta-computing system as a typical multi-cluster system. Since the heterogeneity is becoming common in such systems, we take into account network as well as cluster size heterogeneity to propose the model. To this end, we present an analytical network model and validate the model through comprehensive simulation. The results of the simulation demonstrated that the proposed model exhibits a good degree of accuracy for various system organizations and under different working conditions.     

Performance evaluation of multicast communication in packet-switched networks

In this paper we describe the theoretical background and practical application of QNA-MC (queueing network analyser supporting multicast), a tool for the analytical evaluation of multicast protocols. QNA-MC is based on the QNA method, which (approximately) analyses open networks of GI|G|m queues. In contrast to standard QNA, QNA-MC allows for the specification and evaluation of multicast routes. As in real multicast communication, packets leaving a particular node can be copied and deterministically routed to several other nodes. In order to analyse such queueing networks, QNA-MC converts the multicast routes to a suitable input for standard QNA. From the results delivered by QNA, QNA-MC then derives several performance measures for multicast streams in the network. A validation of QNA-MC, via a comparison to simulation results, shows that QNA-MC yields very good results. Finally, we give a detailed application example by evaluating different multicast routing algorithms for a realistic video conferencing scenario in the European MBONE.     

Performance analysis of adaptive multipath load balancing in WDM–LOBS networks

The rapid advances in optical transmission technology have led to a wide deployment of WDM-based networks, and OBS is considered as a promising switching technology in the optical domain.

A major problem in OBS is undoubtedly burst contention. Different mechanisms to reduce burst loss probability have been proposed, but multipath routing has many advantages and it is a relatively little explored alternative in the scope of OBS networks.

Two interesting adaptive multipath mechanisms for OBS (AARA and GPMR) have been proposed in the literature, but both of them assume that all the interfaces have total wavelength conversion capacity. However, it is expected this feature to be gradually introduced, giving rise to heterogeneous scenarios where different types of interfaces coexist.

Although AARA is applicable to heterogeneous scenarios, GPMR must be slightly modified. We propose this modification and an interesting practical implementation for GPMR. Finally, it is shown that both solutions work satisfactorily well for homogeneous scenarios, but the modified GPMR works clearly better than AARA for heterogeneous scenarios.

On the other hand, by means of a general traffic model at the burst level, and through exhaustive simulation experiments, we study the effect of the correlation structure and of the marginal distribution of the traffic arrival pattern on the burst losses.     

A note on models for non-probabilistic analysis of packet switching networks

We consider two models commonly used in the literature to model adversarial injection of packets into a packet switching network. We establish the relation between these two types of models, and between them and the set of sequences of packets that allow stability. We also consider the adaptive setting in which packets are injected with only their source and destination but without a prescribed path to follow.     

Performance analysis of fast reservation protocols in ATM networks

In Asynchronous Transfer Mode (ATM) networks, VP/VC establishment and bandwidth reservation can be separately performed. Fast Reservation Protocol (FRP), a recently proposed protocol, utilizes this unique feature of the ATM technology to accomplish an efficient use of bandwidth. In FRP, a protocol data unit is called a burst, and a source requests the bandwidth reservation for each burst transmission on the established connection. In this paper, we provide an exact analysis for a class of FRP to obtain the burst delay distribution. Another feature of ATM is that the transmission rate can be set freely if it is admitted by the network. In our modeling, this feature is also incorporated in such a way that the requested bandwidth is reduced if the first attempt to reserve bandwidth is rejected by the network. Through numerical examples, appropriate values of control parameters such as the requested transmission rates are examined to show an effectiveness of FRP. The influences of the propagation delay and overhead due to control cells are also investigated by introducing an approximate technique.     

Performance analysis of large systems

A hybrid analytic and experimental approach to the analysis of large systems is described. The approach is iterative under the assumption that a correct analysis will not be made first time. It is primarily aimed at the analysis of the performance effect of proposed changes prior to coding them. The requirement is for a fairly approximate analysis that is easy to make. The approach is illustrated by an experiment on a relational database system but we believe it to be applicable to many kinds of large systems. The different reasons for analysing performance of a system are discussed and then the ways of approaching the analysis, with an outline of our approach. The details of our approach are given, and illustrated by our experiment.     

Performance of ad hoc networks with two-hop relay routing and limited packet lifetime (extended version)

We consider a mobile ad hoc network consisting of three types of nodes (source, destination and relay nodes) and using the two-hop relay routing. This type of routing takes advantage of the mobility and the storage capacity of the nodes, called the relay nodes, in order to route packets between a source and a destination. Packets at relay nodes are assumed to have a limited lifetime in the network. Nodes are moving inside a bounded region according to some random mobility model. Closed-form expressions and asymptotic results when the number of nodes is large are provided for the packet delivery delay and for the energy needed to transmit a packet from the source to its destination. We also introduce and evaluate a variant of the two-hop relay protocol that limits the number of generated copies in the network. Our model is validated through simulations for two mobility models (random waypoint and random direction mobility models), and the performance of the two-hop routing and of the epidemic routing protocols are compared.     

Performance analysis of ad-hoc routing in heterogeneous clustered multi-hop wireless networks

This paper analyzes the performance of clustered decode-and-forward multi-hop relaying (CDFMR) wireless Rayleigh fading networks, and sheds light on their design principles for energy and spectral efficiency. The focus is on a general performance analysis (over all SNR range) of heterogeneous wireless networks with possibly different numbers of relays in clusters of various separations. For clustered multi-hop relaying systems, hop-by-hop routing is known as an efficient decentralized routing algorithm which selects the best relay node in each hop using local channel state information. In this article, we combine hop-by-hop routing and cooperative diversity in CDFMR systems, and we derive (i) a closed-form expression for the probability distribution of the end-to-end SNR at the destination node; (ii) the system symbol error rate (SER) performance for a wide class of modulation schemes; and (iii) exact analytical expressions for the system ergodic capacity, the outage probability and the achievable probability of the SNR (power) gain. We also provide simple analytical asymptotic expressions for SER and the outage probability in high SNR regime. Numerical results are provided to validate the correctness of the presented analyses.     

Performance modeling of the LEACH protocol for mobile wireless sensor networks

In many wireless sensor network applications, nodes are mobile, while many protocols proposed for these networks assume a static network. Thus, it is important to evaluate if a traditional protocol designed for a static network can tolerate different levels of mobility. This paper provides an analytic model to investigate the effect of mobility on a well-known cluster-based protocol, LEACH. The model evaluates data loss after construction of the clusters due to node mobility, which can be used to estimate a proper update interval to balance the energy and data loss ratio. Thus, the results can help the network designer to adjust the topology update interval given a value of acceptable data loss threshold. A practical approach to increase the mobility tolerance of the protocol is applying a buffer zone to the transmission ranges of the nodes. The model is extended in order to consider the effect of buffer zone. To validate the analytic evaluations, extensive simulations are conducted and correctness of the evaluations is tightly verified.     

一类具有排队现象的工作流图的性能分析

基于极大代数方法,描述一类具有排队现象的工作流图中AND和XOR的时间逻辑关系.AND逻辑表示输出事件当且仅当输入事件都完成时发生,XOR逻辑表示在数个输入事件中按概率只有一个会发生并导致输出事件的发生.以AND和XOR基本模块构建这类工作流图模型,进行系统的性能分析,并给出顾客输出时间间隔下界的估计方法.通过实例仿真验证了建模、分析方法的可行性和有效性.     

Strong Menger connectivity with conditional faults on the class of hypercube-like networks

In this paper, we study the Menger property on a class of hypercube-like networks. We show that in all n-dimensional hypercube-like networks with n−2 vertices removed, every pair of unremoved vertices u and v are connected by min{deg(u),deg(v)} vertex-disjoint paths, where deg(u) and deg(v) are the remaining degree of vertices u and v, respectively. Furthermore, under the restricted condition that each vertex has at least two fault-free adjacent vertices, all hypercube-like networks still have the strong Menger property, even if there are up to 2n−5 vertex faults.