Link-disjoint Paths Research Articles

모바일 애드혹 네트워크에서의 AODV 기반 치대 비중첩 다중경로 라우팅 프로토콜

모바일 애드혹 네트워크(MANET)는 어떤 고정 기반구조나 중앙 집중형 관리 구조를 갖지 않는 모바일 노드의 집합으로 구성된다. AODV (Ad hoc On-demand Distance Vector routing)는 MANET용 온디맨드(on-demand) 라우팅 프로토콜로서, IETF (Internet Engineering Task Force)의 MANET 워킹 그룹에 제출된 기고문(Internet Draft)이다. 본 논문에서는 최대의 노드 비중첩 및 링크 비중첩을 제공하고, AODV 프로토콜은 물론 기존의 AODV 기반 다중경로 프로토콜보다 성능이 우수한 새로운 최대 비중첩 다중경로 AODV (MDAODV) 프로토콜을 제안한다. 본 연구의 핵심 아이디어는 경로 요청(RREQ:Route REQuest) 메시지에 소스 라우팅(source routing) 주소 정보를 추가시켜 확장하는 것과 수신 노드가 일정 시간 동안 도착한 다수의 RREQ를 조사하여 2개의 경로를 선택하는 것이다. 제안한 MDAODV 프로토콜은 기존 다중경로 라우팅 프로토콜에 비해 높은 신뢰성과 우수한 견고성을 갖는 경로를 제공할 뿐만 아니라, 수신 노드에서 경로를 결정하므로 중간 노드에서의 오버헤드를 감소시킨다. 성능평가 결과에 의하면, 제안한 MDAODV 프로토콜은 기존의 AODV 기반 다중경로 프로토콜보다 패킷 전달율과 평균 지연시간의 측면에서 성능이 우수한 반면 라우팅 오버헤드는 오히려 감소하는 경향을 나타낸다. A mobile ad hoc network (MANET) is a collection of mobile nodes without any fixed infrastructure or my form of centralized administration such as access points and base stations. The ad hoc on-demand distance vector routing (AODV) protocol is an on-demand routing protocol for MANETs, which is one of the Internet-Drafts submitted to the Internet engineering task force (IETF) MANET working group. This paper proposes a new multipath routing protocol called maximally disjoint multipath AODV (MDAODV), which exploits maximally node- and link-disjoint paths and outperforms the conventional multipath protocol based on AODV as well as the basic AODV protocol. The key idea is to extend only route request (RREQ) message by adding source routing information and to make the destination node select two paths from multiple RREQs received for a predetermined time period. Compared to the conventional multipath routing protocol, the proposed MDAODV provides more reliable and robust routing paths and higher performance. It also makes the destination node determine the maximally node- and link-disjoint paths, reducing the overhead incurred at intermediate nodes. Our extensive simulation study shows that the proposed MDAODV outperforms the conventional multipath routing protocol based on AODV in terms of packet delivery ratio and average end-to-end delay, and reduces routing overhead.

Using mesh and multi-ring methods in the design of survivable wavelength-routed all-optical networks

This paper presents a comprehensive investigation of a wide range of protection strategies against all single link failures in all-optical wavelength division multiplexing (WDM) networks based on mesh and multi-ring architectures. In the mesh architecture, three protection strategies namely, minimal cost, single link basis and disjoint path protection strategies are investigated. In the multi-ring architecture, the distribution and non-distribution traffic multi-ring design strategies are extensively examined. Although, the concepts of mesh and multi-ring designs have previously been perceived to be fundamentally different, in this paper, we shall explain and show that these two architectures can be systematically related and viewed as a unified concept. This new way of looking at the fully survivable network design helps us to understand clearly the mechanisms and performance of each protection strategy. In addition, this approach allows us to see the trend of fiber-cost requirements that increase step-by-step from the most complicated mesh protection to the simplest multi-ring protection architectures. To minimize the system cost of 100% protection WDM networks, mathematical models based on the integer linear programming (ILP) are derived as the tool for achieving optimal path placement, wavelength assignment and ring selection simultaneously. Apart from the mathematical model, the main contributions of this paper are the analysis and comparison in aspects of the spare capacity requirement and ease of operation and practical feasibility amongst these protection strategies. However, the emphasis will be on the multi-ring protection schemes. In addition, the influence of the number of multiplexed wavelengths per fiber to design outcomes and the benefit of having wavelength conversion capability in WDM network environment are also studied. Copyright © 2004 AEI.

Dynamic Establishment of Segmented Protection Paths in Single and Multi-Fiber WDM Mesh Networks

Wavelength division multiplexed (WDM) networks are matured to provide, scalable data centric infrastructure, capable of delivering flexible, value added, high speed and high bandwidth services directly from the optical (WDM) layer. But, providing fault-tolerance at an acceptable level of overhead in these networks has become a critical problem. This is due to the size of the current and future networks and diverse quality of service (QoS) requirements for multimedia and mission critical applications. Several distributed real-time applications require communication services with fault-tolerance apart from guaranteed timeliness at acceptable levels of overhead. Several methods exist in the literature which attempt to guarantee recovery in a timely and resource efficient manner. These methods are centered around a priori reservation of network resources called spare resources along a protection path. This protection path is usually routed from source to destination along a totally link disjoint path from primary path. This paper considers the problem of routing and wavelength assignment (RWA) in wavelength routed WDM optical networks. In particular, we propose an efficient algorithm to select routes and wavelengths to establish dependable connections (D-connections), called segmented protection paths. Our algorithm does not insist on the existence of totally disjoint paths to provide full protection. We present experimental results which suggest that our scheme is attractive enough in terms of average call acceptance ratio, spare wavelength utilization, and number of requests that can be satisfied for a given number of wavelengths assuming that the requests come one at time, and wavelengths are assigned according to fixed ordering. Furthermore, the results suggest that our scheme is practically applicable for medium and large sized networks, which improves number of requests that can be satisfied and helps in providing better QoS guarantees such as bounded failure recovery time and propagation delays without any compromise on the level of fault-tolerance for a given number of wavelengths and fibers. We conduct extensive simulation experiments to evaluate the effectiveness of the proposed scheme on different networks and compare with existing methods.

Multi-path selection for multiple description video streaming over overlay networks

Real-time media distribution over the Internet poses several challenging problems due to its stringent delay/loss requirements and complex network dynamics. A promising approach to alleviate the severe impacts of these dynamics is to transmit the media over diverse paths. For such an environment, multiple description (MD) coding has been previously proposed to produce multiple independently decodable streams that are routed over partially link–disjoint (non-shared) paths for combatting bursty packet losses and error propagation. However, selecting these paths appropriately is fundamental to the success of MD streaming and path diversity. Hence, in this paper we develop models for MD streaming over multiple paths and based on these models we propose a multi-path selection method that chooses a set of paths maximizing the overall quality at the client under various constraints. The simulation results with MPEG-2 show that sizeable average peak signal-to-noise ratio (PSNR) improvements (ranging from 0.73 to 6.07 dB) can be achieved when the source video is streamed over intelligently selected multiple paths as opposed to over the shortest path or maximally link–disjoint paths. In addition to the PSNR improvement, end-users experience a more continual, i.e., uninterrupted, streaming quality. Our work also considers the architecture and mechanisms by which multi-path streaming can be accomplished over a conventional IP network.

Routing permutations with link-disjoint and node-disjoint paths in a class of self-routable interconnects

We consider efficiently routing permutations in a class of switch-based interconnects. Permutation is an important communication pattern in parallel and distributed computing systems. We present a generic approach to realizing arbitrary permutations in a class of unique-path, self-routable interconnects. It is well-known that this type of interconnect has low hardware cost, but can realize only a small portion of all possible permutations between its inputs and outputs in a single pass. We consider routing arbitrary permutations with link-disjoint paths and node-disjoint paths in such interconnects in a minimum number of passes. In particular, routing with node-disjoint paths has important applications in emerging optical interconnects. We employ and further expand the Latin square technique used in all-to-all personalized exchange algorithms for this class of interconnects for general permutation routing. Our implementation of permutation routing is optimal in terms of the number of passes that messages are transmitted through the network, and it is near-optimal in network transmission time for sufficiently long messages. The possibility of adopting a single-stage interconnect is also discussed.

Heuristic for the maximum disjoint paths problem in wavelength-routed networks with shared-risk link groups [Invited

We tackle the problem of finding the maximum number of link-disjoint paths between a pair of source-destination nodes in wavelength-routed networks, subject to the shared-risk link group (SRLG) constraints. We propose a simple heuristic algorithm whose main idea is to iteratively find the path with the minimum total weight of all the SRLGs through which it passes until no further path can be found, where the weight of each SRLG is basically proportional to its size, and those SRLGs appearing in the minimum cut between the source-destination nodes are assigned higher weights. Extensive simulation results show that the proposed method, with a complexity comparable to that of the simplest conventional k-shortest-path algorithm, steadily outperforms the best existing method.

Ad hoc on-demand multipath distance vector routing

We present AOMDV, an on-demand multipath distance vector protocol for mobile ad hoc networks. AOMDV is based on a prominent on-demand single path protocol called AODV. AOMDV establishes multiple loop-free and link-disjoint paths. Performance comparison of AOMDV with AODV using ns-2 simulations under varying node speeds shows that AOMDV provides a factor of two improvement in delay and about 20% reduction in routing overhead, while having similar packet delivery fraction.

A simple dynamic integrated provisioning/protection scheme in IP over WDM networks

This article presents a simple integrated provisioning/protection scheme to dynamically allocate restorable bandwidth guaranteed paths in IP over WDM networks. A guaranteed restorable path implies that a flow of data is successfully routed if both an active path and another alternate link-disjoint path are found at the same time. Unlike the conventional approach, where the IP and WDM layers are not aware of each other, the new scheme takes advantage of the development in generalized multi-protocol label switching (GMPLS) to provide integrated end-to-end survivability by incorporating network state information from both layers (e.g., the cost information in physical links, the bandwidth usage on each lightpath, and intermediate router speed) into protection path allocation. Simulation results are used to evaluate the performance of the new scheme and show that the proposed protection approach can efficiently improve the network utilization, and deliver reliable services.

Reconfiguration for service and self-healing in ATM networks based on virtual paths

This paper presents a reconfiguration scheme resulting in capacity efficiency and fast restoration by utilizing the inherent benefits of Virtual Paths in ATM networks. The unified optimization of bandwidth reconfiguration is addressed so that switched ATM networks can support both service and survivability from a common pool of network spare capacity at a given time. The spare capacity is composed of idle bandwidth and freed up bandwidth from the switch pairs which have a surplus bandwidth. Fast restoration can be achieved by using the pre-optimized network spare bandwidth and preplanned backup Virtual Paths based on the link and node disjoint path routing scheme. The overall operation of the proposed self-healing strategy can be consolidated into distributed fault management functions at ATM layer based on Virtual Paths. The scheme enables a logical Virtual Paths ring protection switching in ATM networks.

Very Efficient Cyclic Shifts on Hypercubes

Cyclic shifts are intrinsic operations in many parallel algorithms. Therefore, it is important to execute them efficiently. In this note, we present and analyze an algorithm for the cyclic shift operation onn-dimensional (distributed memory) hypercubes. On asynchronous hypercubes, we have shown that all previously known algorithms for cyclic shifts need local message buffers. In order to overcome this, we present an algorithm that always uses link-disjoint paths for routing. We prove that by using this algorithm, any cyclic shift can be realized by using at most 4/3nsteps, without using any local message buffers.

Comparison of k-shortest paths and maximum flow routing for network facility restoration

In the development of technologies for span failure restoration, a question arises about the restoration rerouting characteristics to be specified. In theory, maximal rerouting capacity is obtained with a maximum flow (Max Flow) criterion. However, rerouting that realizes the k-successively shortest link disjoint paths (KSP) may be faster, easier, and, in distributed implementation, more robust than a distributed counterpart for Max Flow. The issue is, therefore, what the restoration capacity penalty is if KSP is used instead of Max Flow. To explore this tradeoff, the authors present a comparative study of the effectiveness of KSP versus Max Flow as an alternative rerouting criteria in the context of transport network span restoration. The comparison applies to both centrally controlled and distributed restoration systems. Study methods include exhaustive span failure experiments on a range of network models, and parametric and analytical investigations for insight into the factors resulting in KSP versus Max Flow differences. The main finding is that KSP restoration capacity is more than 99.9% of that from Max Flow in typical network models. The hypothesis is made that a generalized "trap" topology is responsible for all KSP-Max Flow capacity differences. The hypothesis is tested experimentally and used to develop analytical bounds which agree well with observed results. These findings and data are relevant to standards makers and equipment developers in specifying and engineering future restorable networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>