A mutual alternative routing model for circuit-switched networks

Security measures are being applied in the Telecom Eireann trunk telephone network to minimise disruption due to excess traffic or system failure. Dynamic measures, such as network management, will be deployed in the very near future, but in the meantime static measures are being applied. Geographically separate exchanges of the same status are provided at major nodes with traffic shared equally between them on separate transmission links. Rerouting is provided automatically when a system fails, but at a reduced grade of service. The paper presents a model which simulates this concept of mutual alternative routing using the UNIX-based OPNET (Optimised Network Engineering Tools) package     

Static and dynamic approaches to modeling end-to-end routing in circuit-switched networks

We present two routing strategies, identified herein as static least loaded routing (SLLR) and dynamic least loaded routing (DLLR). Dynamic routing in circuit-switched networks has been an active research topic. The literature to date in this area has focused on how to choose the "best" alternate route for overflow traffic from a direct route, within a network setting referred to as the backbone network. The traffic type considered in the literature has typically been one with a single destination. Least loaded routing (LLR) is an example of a state-dependent routing that selects the least loaded two-link alternate route when traffic overflows from the direct route. Motivated by the development of an emerging traffic type, called multidestination traffic, whose destination is not necessarily limited to a single location, we provide two routing strategies that deal with both the routing of the multiple-destination traffic to the extended network dimension, which is referred to as the destination network, and the routing of the backbone network traffic via LLR. In selecting the destination for multidestination traffic, SLLR employs static information, whereas DLLR employs real-time load status information concerning the destination links. We develop fixed-point models for both DLLR and SLLR. We also validate and compare the models through simulation. The results suggest that DLLR outperforms SLLR in all the scenarios, demonstrating the benefit of state-dependent routing in an end-to-end network. Further, the DLLR scheme improves if an "incident preference" rule is adopted; the rule allows a multidestination call to first choose the incident destination link, if any.     

Call queueing in circuit-switched networks

Consider a circuit-switched network whereC source switches are connected to a destination switch via a tandem switch. Circuit-switched networks traditionally employ a Blocked Calls Lost (BCL) call admission control: a call is rejected if all access circuits from the originating switch to the tandem switch are busy, or if allB outgoing circuits from the tandem switch to the destination switch are busy. This paper investigates a simple extension to the BCL control. Rather than reject all blocked calls, the Blocked Calls Queued (BCQ) control holds some blocked calls by storing their call signalling information in a buffer at the tandem switch. These calls will later be connected when circuits become available. The BCQ model is solved using standard methods requiring O(BC) storage locations and O(B ² C) arithmetic operations. We show that the BCQ control becomes effective if calls are rejected (source rejection) when all access circuits are busy. We demonstrate that the BCQ control with source rejection achieves a substantial reduction in the loss probability at the expense of a small connection delay.This work was supported by a grant from the Foundation for Research Development Communications Systems Programme.     

Analysis of rerouting in circuit-switched networks

Dynamic routing has been adopted in circuit-switched networks in many parts of the world. Most of the routing algorithms used are least loaded routing (LLR) based for its simplicity and efficiency. Rerouting is the practice of routing calls on alternate paths back to direct paths or to other less congested alternate paths. It allows the continuous redistribution of network loads for the relief of the congestion on direct paths. In this paper, we present an original analysis of an LLR-based rerouting scheme. Through numerical examples and confirmation by computer simulation, the throughput gain of rerouting is established     

Packet delay in optical circuit-switched networks

A framework is provided for evaluation of packet delay distribution in an optical circuit-switched network. The framework is based on a fluid traffic model, packet queueing at edge routers, and circuit-switched transmission between edge routers. Packets are assigned to buffers according to their destination, delay constraint, physical route and wavelength. At every decision epoch, a subset of buffers is allocated to end-to-end circuits for transmission, where circuit holding times are based on limited and exhaustive circuit allocation policies. To ensure computational tractability, the framework approximates the evolution of each buffer independently. "Slack variables" are introduced to decouple amongst buffers in a way that the evolution of each buffer remains consistent with all other buffers in the network. The delay distribution is derived for a single buffer and an approximation is given for a network of buffers. The approximation entails finding a fixed point for the functional relation between the "slack variables" and a specific circuit allocation policy. An analysis of a specific policy, in which circuits are probabilistically allocated based on buffer size, is given as an illustrative example. The framework is shown to be in good agreement with a discrete event simulation model.     

Performance analysis and fault tolerance of randomized routing on Clos networks

Beside universality and very low latency, Youssef's randomized self-routing algorithms [25] have high tolerance for multiple faults and more strikingly have the potential for fault tolerance without diagnosis. In this paper we study the performance of Youssef's routing algorithms for faulty Clos networks in the presence of multiple faults in multiple columns with and without fault detection. We show that with fault detection and diagnosis, randomized routing algorithms provide scalable, very efficient and fault tolerant routing mechanisms. Without fault detection and diagnosis, randomized routing provides good fault tolerance for faulty switches in either the first or the second column. The delays become large for faults in the third column or for faults in more than one column. In conclusion, randomized routing enables the system to run without periodic fault detection/diagnosis, and if and when the performance degrades beyond a certain threshold, diagnosis can be performed to improve the routing performance. This revised version was published online in June 2006 with corrections to the Cover Date.     

A taxonomy of rerouting in circuit-switched networks

In circuit-switched networks it is well known that dynamic routing can provide significant throughput gain over fixed routing. Rerouting is the practice of routing calls currently on alternate paths to direct paths or other less congested alternate paths. Previous studies have shown that rerouting can not only increase the throughput of dynamic routing, but also maintain network stability without the need for trunk reservation. This article presents a taxonomy of rerouting in circuit-switched networks showing the various ways rerouting can be designed. In addition, a comparative study on a number of rerouting schemes are performed in a uniformly loaded, fully connected circuit-switched network     

Path selection in user-controlled circuit-switched optical networks

User-controlled circuit-switched optical networks are gaining popularity in an effort to fulfill the insatiable data transport needs of the online community. In this paper we consider the resource allocation challenges that arise in such networks, in particular problems related to construction of end-to-end lightpaths for carrying large multimedia streams. Specifically, we discuss variations of the least cost and widest path problems that address two unique aspects of the user-controlled environment. First, since network resources are exposed for user-control using a service-oriented software control plane, each lightpath is subject to an expiry time. Second, because Wavelength Division Multiplexing (WDM) and resource partitioning introduces multiple redundant paths, classic least cost path computations tend to yield multiple optimal solutions, and so it is useful to break ties among these in a judicious manner. We present polynomial-time path selection techniques that address these issues using efficient data structures. We also show the benefit of breaking ties in shortest path computations in a manner that reduces harmful fragmentation of capacity.     

Performance of routing schemes in wireless personal networks

Routing efficiency in wireless communication networks depends critically on the propagation of location information into the network. We propose new dynamic traffic and state‐dependent routing algorithms which are suitable for the demands of future wireless personal communications networks. Copyright © 1999 John Wiley & Sons, Ltd.     

基于PSO的OBS路由优化选择算法研究

光突发交换(OBS)被认为是下一代光交换技术.利用粒子群优化算法(PSO)对OBS网络路由优化选择问题进行了研究和分析,仿真结果表明,基于PSO的OBS路由算法在计算代价方面要优于传统的最短路径算法,结论对改进OBS的路由选择协议有一定的理论指导意义.     

Behaviour of circuit-switched multistage networks in presence of memory hot spot

Addresses the important problem of evaluating the performance of tightly coupled multiprocessor systems under memory hot spot traffic by presenting an interference analysis of multistage interconnection networks (MINs) for such systems. It is shown that the tree saturation effect does not occur in nonblocking circuit-switched MINs.<>     

General criterion for decomposition of exact blocking computationin circuit-switched networks

The criterion for the decomposition of the computation of blocking probabilities in circuit-switched networks is given. As the criterion does not depend on the network topology or the traffic distribution, more efficient decomposition can be obtained accordingly     

Comparative evaluations of randomized and dynamic routingstrategies for circuit-switched networks

The performances of two classes of routing algorithms, randomized and deterministic, are evaluated and compared in terms of revenue generated and link failures. The randomized algorithm evaluated is dynamic alternate routing, and for the deterministic algorithm, attempts to carry a call are made in a specific precomputed order. The design of the routing sequences depends upon analytic approximations based on fixed-point equations to evaluate network performance and heuristics for the complicated problem of network revenue maximization. The control mechanism of trunk reservations is shown to play an important role in all cases. The performances of the algorithms were evaluated on a fully connected six-node network, the data for which were extracted from a realistic network. The design tools, time constants of various algorithms, and hybrid algorithms developed using the evaluation results are described     

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on‐demand provisioning of wavelength‐routed channels with service‐differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol (IP) network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing (WDM) technologies. Because of the availability of ultra long‐reach transport and all‐optical switching, the deployment of all‐optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video‐on‐demand systems, real‐time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment (RWA). The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call‐blocking probability. The dynamic traffic‐grooming problem in wavelength‐routed networks is generally a two‐layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance engineering of metropolitan area optical networks through impairment constraint routing

We demonstrate the use of impairment constraint routing for performance engineering of transparent metropolitan area optical networks. Our results show the relationship between blocking probability and different network characteristics such as span length, amplifier noise figure, and bit rate, and provide information on the system specifications required to achieve acceptable network performance.     

Performance analysis of cellular networks

Dynamic channel allocation can reduce the probability of blocking in cellular telephone networks. However, more is needed to achieve optimal performance. The author aims at estimating the minimal blocking probability for some simple cellular networks. Some dynamic channel allocation strategies are analyzed, the optimal performance (obtained by dynamic allocation and flow control) of some very simple networks is computed, and simple bounds on optimal performance are presented. These results lead to a better understanding of cellular networks and can be used to evaluate new control algorithms     

Multipath multihop routing analysis in mobile ad hoc networks

This paper proposes an analytical modeling framework to investigate multipath routing in multihop mobile ad hoc networks. In this paper, a more generalized system has been considered and mathematically analyzed to observe some of the related performance measures of the ad hoc network. Each node in the network is assumed to have finite buffer. The single-path model is approximated to be a multi-node M/M/1/B tandem network, and the multi-path model as a set of multiple parallel paths. This proposed model allows us to investigate issues such as end-to-end delivery delay, throughput and routing reliability in mobile ad hoc networks. Theoretical results have been verified by numerical results. An optimal path selection strategy has been proposed to select a minimized delay path among the available multiple paths between source-destination pair.     

Message delay and queue-size analysis for circuit-switched TDMAsystems

A multiple-access communications channel which is shared among network stations using a circuit-switched time-division multiple-access (CS-TDMA) scheme is examined. Each station is allocated a fixed number of slots (N) during each frame. The authors carry out queue-size message delay analysis for CS-TDMA systems. They derive the generating function of the queue size and of the waiting time distribution for a discrete-time Geom^[x]/Geom/N queuing system. This result is used to obtain the generating function of the system size for the CS-TDMA scheme. The associated computation requires the solution of (N+1)2^N linear equations. To derive a more computationally effective procedure, tight lower and upper bounds are obtained, requiring the solution of at most 3N linear equations. The authors prove that a slot allocation scheme which distributes station slots uniformly over the frame yields a message delay lower bound. The application of the results to the analysis of demand-assigned CS-TDMA systems is also discussed