Dynamic Routing Scheme Research Articles

Demonstration of Deflection Routing With Layer-2 Evaluation at 40 Gb/s in a Three-Node Optical Burst Switching Testbed

We developed an optical burst switching (OBS) network testbed with three nodes, where each node consisted of a fast 5 5 (Pb,La)(Zr,Ti)O optical matrix switch. A newly developed Ether frame media converter was successfully used to evaluate Layer-2 performance of the testbed, with a line rate of 40Gb/s. A dynamic deflection routing scheme for contention resolution is implemented. Error-free switching with 40-Gb/s payload was achieved over the three nodes, promising low frame loss due to dynamic operation. By comparing effects of random collision with and without deflection routing for varying loads, we demonstrate that near-theoretical low frame loss is achievable in fast Layer-2 (Ether frame) transport over OBS networks.

An enhanced dynamic multilayer routing for networks with protection requirements

This paper presents a new enhanced dynamic and multi-layer protection (DMP) routing scheme that considers cooperation between packet and wavelength switching domain in order to minimize the resource consumption. The paper describes the architecture of the multilayer network scenario and compares the proposed algorithm with other routing mechanisms applying protection at the IP/multi-protocol label switching (MPLS) layer or at the optical layer. Simulation results show that DMP reduces the number of optical-electrical-optical (o-e-o) operations and makes an efficient use of the network resources compared to non-multilayer proposals.

Informationally Decentralized Video Streaming Over Multihop Wireless Networks

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Various packet scheduling, dynamic routing, error-protection, and channel adaptation strategies have been proposed at different layers of the protocol stack to address multi-user video streaming over multihop wireless networks. However, these cross-layer transmission strategies can be efficiently optimized only if they use accurate information about the network conditions and hence, are able to timely adapt to network changes. Due to the informationally decentralized nature of the multihop wireless network, performing centralized optimization for delay-sensitive video streaming application based on global information about the network status is not practical. Distributed solutions that adapt the transmission strategies based on timely information feedback need to be considered. To acquire this information feedback for cross-layer adaptation, we deploy an overlay infrastructure, which is able to relay the necessary information about the network status and incurred delays across different network “horizons” (i.e., across a different number of hops in a predetermined period of time). In this paper, we propose a distributed streaming approach that is optimized based on the local information feedback acquired from the various network horizons. We investigate the distributed cross-layer adaptation at each wireless node by considering the advantages resulting from an accurate and frequent network information feedback from larger horizons as well as the drawbacks resulting from an increased transmission overhead. Based on the information feedback, we can estimate the <emphasis emphasistype="italic">risk</emphasis> that packets from different priority classes will not arrive at their destination before their decoding deadline expires. Subsequently, the various transmission strategies such as packet scheduling, retransmission limit and dynamic routing policies are adapted to jointly consider the estimated risk as well as the impact in terms of distortion </para>

Dynamic online QoS routing schemes: Performance and bounds

Several dynamic QoS routing techniques have been recently proposed for new IP networks based on label forwarding. However, no extensive performance evaluation and comparison is available in the literature. In this paper, after a short review of the major dynamic QoS routing schemes, we analyze and compare their performance referring to several networks scenarios. In order to set an absolute evaluation of the performance quality we have obtained the ideal performance of any routing scheme using a novel and flexible mathematical programming model that assumes the knowledge of arrival times and duration of the connections offered to the network. This model is based on an extension of the maximum multi-commodity flow problem. Being an integer linear programming model, its complexity is quite high and its evaluation is constrained to networks of limited size. To overcome the computational complexity we have defined an approximate model, based on the multi-class Erlang formula and the minimum multi-commodity cut problem, that provides an upper bound to the routing scheme performance. The performance presented in the paper, evaluated by measuring the connection rejection probability, shows that the schemes considered reach, in several scenarios, the ideal performance, showing that no much gain is left for alternate new schemes.

Simplification of network dynamics in large systems

We show that when networks are large significant simplicity can be achieved for pricing-based control. We first consider a general loss network with Poisson arrivals and arbitrary holding time distributions. In dynamic pricing schemes, the network provider can charge different prices to the user according to the current utilization level of the network and also other factors. We show that when the system becomes large the performance (in terms of expected revenue) of an appropriately chosen static pricing scheme, whose price is independent of the current network utilization, will approach that of the optimal dynamic pricing scheme. Further, we show that under certain conditions, this static price is independent of the route that the flows take. We then extend the result to the case of dynamic routing, and show that the performance of an appropriately chosen static pricing scheme with bifurcation probability determined by average parameters can also approach that of the optimal dynamic routing scheme when the system is large. These results deepen our understanding of pricing-based network control. In particular, they provide us with the insight that, when the system is large, an appropriate pricing strategy based on the average network conditions (hence, slowly changing) can approach optimality.

Dynamic routing in translucent WDM optical networks: the intradomain case

Translucent wavelength-division multiplexing optical networks use sparse placement of regenerators to overcome physical impairments and wavelength contention introduced by fully transparent networks, and achieve a performance close to fully opaque networks at a much less cost. In previous studies, we addressed the placement of regenerators based on static schemes, allowing for only a limited number of regenerators at fixed locations. This paper furthers those studies by proposing a dynamic resource allocation and dynamic routing scheme to operate translucent networks. This scheme is realized through dynamically sharing regeneration resources, including transmitters, receivers, and electronic interfaces, between regeneration and access functions under a multidomain hierarchical translucent network model. An intradomain routing algorithm, which takes into consideration optical-layer constraints as well as dynamic allocation of regeneration resources, is developed to address the problem of translucent dynamic routing in a single routing domain. Network performance in terms of blocking probability, resource utilization, and running times under different resource allocation and routing schemes is measured through simulation experiments.

Dynamic multilayer routing schemes in GMPLS-based IP+optical networks

This article presents two dynamic multilayer routing policies implemented in the photonic MPLS router developed by NTT for IP+optical generalized MPLS networks. According to IP traffic requests, wavelength paths called lambda label switched paths are set up and released in a distributed manner based on GMPLS routing and signaling protocols. Both dynamic routing policies first try to allocate a newly requested electrical path to an existing optical path that directly connects the source and destination nodes. If such a path is not available, the two policies employ different procedures. Policy 1 tries to find available existing optical paths with two or more hops that connect the source and destination nodes. Policy 2 tries to establish a new one-hop optical path between source and destination nodes. The performances of the two routing policies are evaluated. Simulation results suggest that policy 2 outperforms policy 1 if p is large, where p is the number of packet-switching-capable ports; the reverse is true only if p is small. We observe that p is the key factor in choosing the most appropriate routing policy. We also describe items that need to be standardized in the IETF to effectively achieve multilayer traffic engineering.

A Maximum Lifetime Data Gathering Algorithm for Wireless Sensor Networks

This paper investigates the maximum lifetime data gathering problem theoretically. Specifically, (1) the simplified static routing scheme where only one routing tree is used to gather data during the lifetime of network is analyzed, (2) the actual dynamic routing scheme where a series of routing trees are used to gather data is analyzed, (3) a near optimal maximum lifetime data gathering and aggregation algorithm MLDGA is proposed, which tries to minimize the total energy consumption in each round and maximize the lifetime of a routing tree used in the round, (4) the MLDGA algorithm is simulated in Java programming language. Comparing with the existing algorithms that are only efficient in some specified conditions, the simulation results show that MLDGA performs well regardless

A dynamic vehicle routing problem with time-dependent travel times

In this paper we present a formulation for the dynamic vehicle routing problem with time-dependent travel times. We also present a genetic algorithm to solve the problem. The problem is a pick-up or delivery vehicle routing problem with soft time windows in which we consider multiple vehicles with different capacities, real-time service requests, and real-time variations in travel times between demand nodes. The performance of the genetic algorithm is evaluated by comparing its results with exact solutions and lower bounds for randomly generated test problems. For small size problems with up to 10 demands, the genetic algorithm provides almost the same results as the exact solutions, while its computation time is less than 10% of the time required to produce the exact solutions. For the problems with 30 demand nodes, the genetic algorithm results have less than 8% gap with lower bounds. This research also shows that as the uncertainty in the travel time information increases, a dynamic routing strategy that takes the real-time traffic information into account becomes increasingly superior to a static one. This is clear when we compare the static and dynamic routing strategies in problem scenarios that have different levels of uncertainty in travel time information. In additional tests on a simulated network, the proposed algorithm works well in dealing with situations in which accidents cause significant congestion in some part of the transportation network.

Tabu Search Algorithm for Dynamic Vehicle Routing Problems Under Real-Time Information

Dynamic vehicle routing strategies have been widely discussed because of advances in information technologies. Dynamic vehicle routing problems are important aspects of commercial vehicle operation applications of intelligent transportation system technologies. One possible operational benefit of real-time information might be the ability to reroute commercial vehicles efficiently according to current traffic conditions. The present effort is aimed at developing a tabu-based dynamic vehicle routing algorithm under real-time information and then evaluating the algorithm in a simulation-assignment framework. Two types of information, historical information and real-time information, are considered in the tabu search algorithms to design temporal as well as spatial tabu lists for route construction and improvement. Numerical experiments conducted with the network of the city of Taichung, Taiwan, are presented to investigate dynamic vehicle dispatching and routing strategies under real-time information supply strategies and to assess the effectiveness of such strategies for traffic incidents.

State-of-the-art progress in developing survivable routing schemes in mesh WDM networks

This article introduces the state-of-the-art progress in developing survivable routing schemes in the optical layer of modern mesh WDM networks. Emphasis is placed on the requirements for achieving survivability that keep stringent service continuity for bandwidth provisioning under any unexpected failure of network infrastructure (e.g., a link, node, or device). We first review the reported dynamic survivable routing schemes that find the least-cost working and protection path-pair for both dedicated and shared protection. With the knowledge of shared risk link group (SRLG), we define the cost function and link-state for solving the protection path for a given working path. This article also discusses the survivable routing schemes for spare capacity allocation that deal with multiple working paths, in which both span-oriented and path-oriented spare capacity allocation schemes will be defined and discussed.

Study of Solution Approach for Dynamic Vehicle Routing Problems with Real-Time Information

Recent advances in commercial vehicle operations (CVO), especially in communication and information technologies, allow the study of dynamic vehicle routing problems under new and updated information, such as traffic conditions and new customers. Two major operational benefits of CVO include ( a) dynamically assigning vehicles to time-sensitive demands, and ( b) efficiently rerouting vehicles according to current traffic conditions. In this research, stochastic vehicle routing problems (SVRP) are considered and extended to incorporate real-time information for dynamic vehicle routing problems. The SVRP model is formulated by a chance-constrained model and is solved by CPLEX with branch-and-bound techniques. Numerical experiments are conducted in a Taichung city network to investigate dynamic vehicle routing strategies under real-time information supply strategies and to assess the effectiveness of such strategies in a dynamic perspective.

A simple fault-tolerant adaptive and minimal routing approach in 3-D meshes

In this paper we propose a sufficient condition for minimal routing in 3-dimensional (3-D) meshes with faulty nodes. It is based on an early work of the author on minimal routing in 2-dimensional (2-D) meshes. Unlike many traditional models that assume all the nodes know global fault distribution or just adjacent fault information, our approach is based on the concept of limited global fault information. First, we propose a fault model called faulty cube in which all faulty nodes in the system are contained in a set of faulty cubes. Fault information is then distributed to limited number of nodes while it is still sufficient to support minimal routing. The limited fault information collected at each node is represented by a vector called extended safety level. The extended safety level associated with a node can be used to determine the existence of a minimal path from this node to a given destination. Specifically, we study the existence of minimal paths at a given source node, limited distribution of fault information, minimal routing, and deadlock-free and livelock-free routing. Our results show that any minimal routing that is partially adaptive can be applied in our model as long as the destination node meets a certain condition. We also propose a dynamic planar-adaptive routing scheme that offers better fault tolerance and adaptivity than the planar-adaptive routing scheme in 3-D meshes. Our approach is the first attempt to address adaptive and minimal routing in 3-D meshes with faulty nodes using limited fault information.

A Novel Distributed Protocol for Path Selection in Dynamic Wavelength-Routed WDM Networks

This paper solves the problem of path selection for WDM mesh networks with a special focus on the implementation in middle-sized networks, such as metropolitan-area networks (MANs). A novel routing and signaling protocol, called asynchronous criticality avoidance (ACA), is proposed to improve the network performance. With the ACA protocol, a specific set of wavelength channels are defined as critical links between a node pair according to dynamic link-state. Criticality information is defined as the critical links and the associated information, which is coordinated and disseminated by each source node to every other source node as an inter-arrival critical coordination. Routing and wavelength assignment is performed along with the criticality avoidance mechanism, in which path selection process is devised to take the criticality information into consideration. Simulation is conducted in 22- and 30-node networks to examine the proposed approach. The simulation results show that the ACA protocol significantly outperforms the fixed-path least-congested (FPLC) and adaptive dynamic routing (ADR) schemes under the fixed alternate routing architecture.

다중무인운반차 시스템의 새로운 동적경로계획 알고리즘 : 비정지우선 우회 알고리즘

We present a new dynamic routing scheme for multiple autonomous guided vehicles (AGVs) systems. There have been so many results concerned with scheduling and routing of multiple AGV systems; however, most of them are only applicable to systems with a small number of AGVs under a low degree of concurrency. With an increased number of AGVs in recent applications, these AGV systems are faced with another problem that has never been occurred in a system with a small number AGVs. This is the stop propagation problem. That is, if a leading AGV stops then all the following AGVs must stop to avoid any collision. In order to resolve this problem, we propose a nonstop preferential detour (NPD) algorithm which is a new dynamic routing scheme employing an election algorithm. For real time computation, we introduce two stage control scheme and propose a new path searching scheme, k-via shortest path scheme for an efficient dynamic routing algorithm. Finally, the proposed new dynamic routing scheme is illustrated by an example.

Static and dynamic low-congested interval routing schemes

Interval routing schemes (IRS) have been extensively investigated in the past years with special emphasis on shortest paths. Besides their theoretical interest, IRS have practical applications, as they have been implemented with wormhole routing in the last generation of INMOS transputer router chips. In this paper we consider IRS that are optimal with respect to the congestion of the induced path system. In fact, wormhole routing is strongly influenced by the maximum number of paths that share a physical link and from low to moderate congestion it outperforms the packet switching technique. We provide a general framework able to deal with the various congestion issues in IRS. In fact, we will distinguish between static cases, in which the source–destination configurations are fixed, and dynamic cases, where they vary over time. All these situations can be handled in a unified setting, thanks to the notion of competitiveness introduced in this paper. We first give some general results not related to specific traffic demands. Then, in the one-to-all communication pattern, we show that constructing competitive IRS for a given network is an intractable problem, both for the static and the dynamic case, that is when the root vertex is fixed and when it can change along the time, respectively. Finally, both for one-to-all and all-to-all communication patterns, we provide nicely competitive k-IRS for relevant topologies. Networks considered are chains, trees, rings, chordal rings and multi-dimensional grids and tori. We consider both the directed congestion case, in which there are pairwise opposite unidirectional links connecting two neighbor processors, and the undirected congestion case, in which two neighbors are connected by a single bi-directional link.

A Fault-tolerant Adaptive and Minimal Routing Scheme in $n$-D Meshes

In this paper a sufficient condition is given for minimal routing in n-dimensional (n-D) meshes with faulty nodes contained in a set of disjoint fault regions. It is based on an early work of the author on minimal routing in low-dimensional meshes (such as 2-D meshes with faulty blocks). Unlike many traditional models that assume all the nodes know global fault distribution, our approach is based on the concept of limited global fault information. First, a novel fault model called Fault Region is proposed in which all faulty nodes in the system are contained in a set of disjoint regions. Fault information is coded in a 2n-tuple called Extended Safety Level associated with each node of an n-D mesh to support minimal routing. Specifically, we study the existence of minimal paths at a given source node, limited distribution of fault information, minimal routing and deadlock-free routing. Our results show that any minimal routing that is partially adaptive can still be applied, as long as the destination node meets a certain safety condition. A dynamic planar-adaptive routing scheme is presented that offers better fault tolerance and adaptivity than the regular planar-adaptive routing scheme in n-D meshes. In 3-D meshes, both regular and dynamic planar-adaptive routing need three virtual channels. Our approach is the first attempt to address minimal routing in n-D meshes with faulty nodes using limited global fault information.

Dynamic multi-path routing

In this paper we study the dynamic multi-path routing problem. We focus on an operating regime where traffic flows arrive at and depart from the network in a bursty fashion, and where the delays involved in link state advertisement may lead to "synchronization" effects that adversely impact the performance of dynamic single-path routing schemes.We start by analyzing a simple network of parallel links, where the goal is to minimize the average increase in network congestion on the time scale of link state advertisements. We consider an asymptotic regime leading to an optimization problem permitting closed-form analysis of the number of links over which dynamic multi-path routing should be conducted. Based on our analytical result we examine three types of dynamic routing schemes, and identify a robust policy, i.e., routing the traffic to a set of links with loads within a factor of the least loaded, that exhibits robust performance. We then propose a similar policy for mesh networks and show by simulation some of its desirable properties. The main results suggest that our proposal would provide significant performance improvement for high speed networks carrying bursty traffic flows.

Evaluation Framework for Dynamic Vehicle Routing Strategies Under Real-Time Information

Dynamic vehicle dispatching and routing strategies are important aspects of commercial vehicle operations applications of intelligent transportation systems technologies. One possible operational benefit of real-time information is the ability to reroute commercial vehicles efficiently according to current traffic conditions. A dynamic evaluation framework in which dispatching and routing strategies for individual vehicles can be tested in a realistic traffic simulation environment is developed. The simulation-assignment model, DYNASMART, is applied to evaluate such strategies in a traffic network. Numerical experiments conducted in the Taichung network are presented to investigate dynamic vehicle dispatching and routing strategies under real-time information supply strategies and to assess the effectiveness of such strategies in a dynamic perspective.

Dynamic multicast routing in VLSI

As real-time applications requiring dynamic group communication emerges, existing multicast routing algorithms must be improved to cater for high-speed routing decisions. Most of the reported efficient multicast routing algorithms for real-time applications construct a multicast tree using the Dijkstra's algorithm. However, they require reconstruction of the tree when there are group membership changes or faulty links/nodes in the session. In this paper, a dynamic routing strategy that does not rely on the construction of the multicast tree is presented. It is based on the “clustering technique” and it lends well for VLSI implementation. The Cluster Unit was implemented using VHDL and a suitable architecture for the routing strategy has been proposed. Performance evaluations based on software simulations show that the proposed routing strategy performs better than the most widely used multicast routing algorithm when the number of nodes become large. Moreover, performance comparisons based on the VHDL implementation of the Cluster Unit show that the proposed technique performs significantly better when realised in VLSI.