A novel recursive shared segment protection algorithm in survivable WDM networks

This paper investigates the problem of dynamic survivable routing for shared segment protection in mesh Wavelength-Division-Multiplexing (WDM) optical networks. We propose a heuristic algorithm, named Recursive Shared Segment Protection (RSSP), to introduce a more flexible way to partition the working path into segments and compute the corresponding backup segments. In RSSP, the working segments cannot be determined before the backup segments are found, we adopt a recursive process to compute the backup segments one by one and then choose an optimized way to partition the working path. The calculations of every neighbor working segment and its backup segment are connected with each other. We constrain the hop count for each backup segment to insure the short failure recovery time and control the bandwidth resource utilization. Compared with the Share Path Protection (SPP), RSSP can achieve much shorter failure recovery time with a little sacrifice in bandwidth resource utilization and RSSP can also perform better compromise between the failure recovery time and the bandwidth resource utilization than the Equal-Length Segment Protection (ELSP) algorithm. We evaluate the effectiveness of RSSP and the results are found to be promising.     

Multiple link failures survivability of optical networks with traffic grooming capability

This paper investigates the problem of survivable traffic grooming (STG) in shared mesh optical networks and proposes different frameworks for improving the survivability of low speed demands against multiple near simultaneous failures. Spare capacity reprovisioning has recently been considered for improving the overall network restorability in the event of dual failures; here, after the recovery form the first failure, some connections in the network may become unprotected and exposed to new failures. Capacity reprovisioning then allocates protection resources to unprotected and vulnerable connections so that the network can withstand a future failure. In this paper, we propose two different reprovisioning schemes (lightpath level reprovisioning, LLR, and connection level reprovisioning, CLR); they differ in the granularity at which protection resources are reprovisioned. Further, each of these schemes is suitable for a different survivable grooming policy. While LLR provides collective reprovisioning of connections at the lightpath level, CLR reprovisions spare bandwidth for lower speed connections instead. We use simulation methods to study the performance of these schemes under two grooming policies (PAL and PAC), and we show that while CLR reprovisions substantially many more connections than LLR (i.e., potentially more management overhead) CLR yields a much better network robustness to simultaneous failures due to its superior flexibility in using network resources.     

Traffic recovery time constrained shared sub-path protection algorithm in survivable WDM networks

With the development of real-time applications, the traffic recovery time, which is defined as the duration between the failure occurrence on the working path and the interruptive traffic has been successfully switched to the backup path, has become the basic Quality-of-Service (QoS) requirement in survivable WDM networks. In this paper, we address the problem of shared sub-path protection with considering the constraint of traffic recovery time and propose a new heuristic algorithm called Traffic recovery time Constrained Shared Sub-Path Protection (TC_SSPP) to compute the working path and the Shared-Risk-Link-Group (SRLG)-disjoint backup sub-paths. The main target of our work is to improve the resource utilization ratio and reduce the blocking probability for dynamic network environment. By properly setting the delay parameter for each link and running the Delay Constrained Shortest Path Algorithm (DCSPA) to compute the backup sub-paths, TC_SSPP can effectively guarantee the traffic recovery time. Simulation results show that the proposed TC_SSPP can outperform the traditional algorithms.     

Protections for multicast session in WDM optical networks under reliability constraints

In this paper, we investigate protections of multicast session under reliability constraints in WDM optical networks, which is not referred in previous works. All of the papers about protection of multicast session discuss 100% reliability that may be distinct in different users’ requirement. At the beginning of the paper, we discuss the reliability of a tree. Then under reliability constraints, we propose three novel protection algorithms, which are Arc-Disjoint Tree with Different Reliability (ADT_DiR), Partial Tree Protection (PTP) and Choosing Segments Protection (CSP). ADT_DiR finds an arc-disjoint tree if the reliability of primary tree does not meet users’ requirement. PTP finds a small protection tree for some part of primary tree and also meets users’ requirement. CSP divides primary tree into segments first, and then protects some segments that are picked up by a strategy while satisfying users’ requirement. Compared with all protection schemes in other papers, which provide 100% reliability, ADT_DiR, PTP and CSP all decrease the resources needed by backup tree and reduce the failure probability of finding backup trees. The simulation results show that all the three protection schemes decrease the blocking ratio and reduce the protection resources consumed comparing to other protection schemes while meeting users’ requirement under dynamic traffics.     

Fast reroute from single link and single node failures for IP multicast

The rise in multicast implementations has seen with it an increased support for fast failure recovery from link and node failures. Most recovery mechanisms augment additional services to existing protocols causing excessive overhead, and these modifications are predominantly protocol-specific. In this paper, we develop a multicast failure recovery mechanism that constructs protocol independent fast reroute paths to recover from single link and single node failures. We observe that single link failure recovery in multicast networks is similar to recovering unicast traffic, and we use existing unicast recovery mechanisms for multicast traffic. We construct multicast protection trees that provide instantaneous failure recovery from single node failures. For a given node x, the multicast protection tree spans all its neighbors and does not include itself. Thus, when the node fails, the neighbors of the node are connected through the multicast protection tree instead of node x, and forward the traffic over the multicast protection tree for the duration of failure recovery. The multicast protection trees are constructed a priori, without the knowledge of the multicast traffic in the network. Based on simulations on three realistic network topologies, we observe that the multicast protection trees increase the routing table size only by 38% on average and the path length between any source–destination pair by 13% on average.     

A new approach for designing fault-tolerant WDM networks

In recent years, path protection has emerged as a widely accepted technique for designing survivable WDM networks. This approach is attractive, since it is able to provide bandwidth guarantees in the presence of link failures. However, it requires allocating resources for backup lightpaths, which remain idle under normal fault-free conditions. In this paper, we introduce a new approach for designing fault-tolerant WDM networks, based on the concept of survivable routing. Survivable routing of a logical topology ensures that the lightpaths are routed in such a way that a single link failure does not disconnect the network. When a topology is generated using our approach, it is guaranteed to have a survivable routing. We further ensure that the logical topology is able to handle the entire traffic demand after any single link failure. We first present an ILP that optimally designs a survivable logical topology, and then propose a heuristic for larger networks. Experimental results demonstrate that this new approach is able to provide guaranteed bandwidth, and is much more efficient in terms of resource utilization, compared to both dedicated and shared path protection.     

A new shared-risk link groups (SRLG)-disjoint path provisioning with shared protection in WDM optical networks

This paper addresses the protection problem in WDM optical networks and presents a New Shared-risk link groups (SRLG)-Disjoint Path Provisioning (NSDPP) approach with shared protection to tolerate the single-risk failure. Comparing to previous Shared-risk link groups (SRLG)-Disjoint Path Provisioning (SDPP) approach, NSDPP is able to obtain better performance, because in NSDPP some primary path and backup paths of other primary paths can share the common resources if the corresponding rules can be satisfied. Simulation results are shown to be promising.     

Nonblocking WDM multicast switching networks

With ever increasing demands on bandwidth from emerging bandwidth-intensive applications, such as video conferencing, E-commerce, and video-on-demand services, there has been an acute need for very high bandwidth transport network facilities. Optical networks are a promising candidate for this type of applications. At the same time, many bandwidth-intensive applications require multicast services for efficiency purposes. Multicast has been extensively studied in the parallel processing and electronic networking community and has started to receive attention in the optical network community recently. In particular, as WDM (wavelength division multiplexing) networks emerge, supporting WDM multicast becomes increasingly attractive. In this paper, we consider efficient designs of multicast-capable WDM switching networks, which are significantly different and, hence, require nontrivial extensions from their electronic counterparts. We first discuss various multicast models in WDM networks and analyze the nonblocking multicast capacity and network cost under these models. We then propose two methods to construct nonblocking multistage WDM networks to reduce the network cost     

PTN网络的二次断纤链路规划算法

在PTN（PacketTransportNetwork）网络规划建设中,需要对光纤链路留出备份带宽,以保证部分光纤断开时,受影响业务有足够的容量进行路由重组。这也是提高网络生存性的有效方法之一。文中首先遍历网络双链路的失效状态,然后断开网络中任意两条链路,通过逐次增加链路容量来保证失效业务能够重组路由;最后提出二次断纤链路容量规划算法并进行试验仿真。结果表明,该算法在节约网络带宽、降低建造成本以及故障容错方面有着良好性能,能够很好应用于传送网络的链路规划中。     

Protection based on backup radios and backup fibers for survivable Fiber-Wireless (FiWi) access network

In Fiber-Wireless (FiWi) access network, the optical back-end is vulnerable to the network component failure due to its tree topology. Any failure at the optical back-end may cause huge data loss. Thus, the survivability in FiWi is an important issue, especially the protection for the optical back-end. Some works propose to protect the optical back-end in FiWi by means of the wireless rerouting in the wireless front-end. However, these works cannot guarantee that there are always the available wireless paths for the traffic rerouting. In this paper, we divide the failures at the optical back-end into ONU-level failure and OLT-level failure according to the failure severity. To tolerate the ONU-level failure, we allocate each ONU a partner ONU and establish the wireless-backup-path between them by deploying backup radios on the traversed wireless routers. To tolerate the OLT-level failure, we cluster all segments in the network and place the backup fibers among the segments in each cluster to establish the protection ring. Thus, each pair of segments in the same cluster can backup for each other along the optical-backup-paths on the protection ring. We propose the heuristic algorithms to minimize the cost of backup radios and the cost of backup fibers. The simulation results demonstrate that the proposed algorithms are effective in enhancing the survivability of FiWi, while requiring less cost than the previous works.     

Building Edge-Failure Resilient Networks

We consider the design of resilient networks that are fault tolerant against link failures. Resilience against link failures can be built into the network by providing backup paths, which are used in the eventuality of an edge failure occurring on a primary path in the network. We consider several network design problems in this context; these problems are motivated by the requirements of current high-speed optical networks. In all the following problems the objective is to provide resilience in networks while minimizing the cost incurred. The main problem under consideration in this paper is that of backup allocation: this problem takes as its input an already provisioned primary network and a parameter k, and allocates backup capacity on the edges of the underlying network so that all the demand can be routed even in the presence of k edge failures. We also consider a variant of this problem where the primary network has a tree topology, and it is required that the restored network retains a tree topology. We then address the problem of simultaneous primary and backup allocation: we are given specifications of the traffic to be handled, and the goal is to provision both the primary as well as the backup network. Finally, we investigate a single-commodity problem motivated by a pragmatic scenario in which the primary network is not known in advance and demands between source--sink pairs arrive online.     

Heuristic algorithms for designing self-repairing protection trees in mesh networks

Protection trees have been used in the past for restoring multicast and unicast traffic in networks in various failure scenarios. In this paper we focus on shared self-repairing trees for link protection in unicast mesh networks. Shared protection trees have been proposed as a relatively simple approach that is easy to reconfigure and could provide sub-second restoration times with sub-optimal redundancy requirement. The self-repairing nature of this class of protection trees may make them an attractive option for cases where dynamic changes in network topology or demand may occur. In this paper, we present heuristic algorithms to design a self-repairing protection tree for a given network. We study the restorability performance of shared trees and examine the limitations of such schemes in specific topologies, such as cases where long node chains exist. Using extensive simulations with thousands of randomly generated network graphs. We compare redundancy and average backup path length of shared protection trees with optimal tree designs and non-tree designs. We also apply our algorithms to the problem of designing the protection tree in a pre-designed fixed-capacity network, and study the performance of shared protection trees in this scenario under different network loads and link utilization levels.     

Comparison of recovery schemes to maximize restorable throughput in multicast networks

Multicast networks have many applications especially in real-time content delivery systems. For high-quality services, users do not expect to witness any interruption; thus, network link failure has to be handled gracefully. In unicast networks there are many approaches for dealing with link failures using backup paths. Recently, Cohen and Nakibly categorized these methods, provided linear programming formulations for optimizing network throughput under the assumption that the paths are splitable, and compared them experimentally. In this work, we take their approach and apply to the multicast failure recovery problem. We propose backup bandwidth allocation algorithms based on linear programs to maximize the throughput, and perform an experimental study on the performance of recovery schemes. We study many recovery schemes in multicast networks and propose a new recovery scheme that performs better than all other recovery scheme except the one that recomputed the whole multicast tree from scratch for each link failure.     

光纤Mesh网络动态组播业务疏导算法

针对当前低速组播业务请求与光网络高速波长传输容量的问题,基于光网络组播业务疏导模型,提出动态组播业务疏导算法,将新的组播业务请求疏导到已建立的光组播树上,达到提高网络资源的利用率、降低组播业务连接阻塞概率的目的。仿真结果表明,该算法可有效地改善网络性能。     

Efficient fault-tolerant routing in multihop optical WDM networks

This paper addresses the problem of efficient routing in unreliable multihop optical networks supported by Wavelength Division Multiplexing (WDM). We first define a new cost model for routing in (optical) WDM networks that is more general than the existing models. Our model takes into consideration not only the cost of wavelength access and conversion but also the delay for queuing signals arriving at different input channels that share the same output channel at the same node. We then propose a set of efficient algorithms in a reliable WDM network on the new cost model for each of the three most important communication patterns-multiple point-to-point routing, multicast, and multiple multicast. Finally, we show how to obtain a set of efficient algorithms in an unreliable WDM network with up to f faulty optical channels and wavelength conversion gates. Our strategy is to first enhance the physical paths constructed by the algorithms for reliable networks to ensure success of fault-tolerant routing, and then to route among the enhanced paths to establish a set of fault-free physical routes to complete the corresponding routing request for each of the communication patterns     

A subtree-based approach to failure detection and protection for multicast in SDN

Software-defined networking (SDN) has received tremendous attention from both industry and academia. The centralized control plane in SDN has a global view of the network and can be used to provide more effective solutions for complex problems, such as traffic engineering. This study is motivated by recent advancement in SDN and increasing popularity of multicasting applications. We propose a technique to increase the resiliency of multicasting in SDN based on the subtree protection mechanism. Multicasting is a group communication technology, which uses the network infrastructure efficiently by sending the data only once from one or multiple sources to a group of receivers that share a common path. Multicasting applications, e.g., live video streaming and video conferencing, become popular, but they are delay-sensitive applications. Failures in an ongoing multicast session can cause packet losses and delay, which can significantly affect quality of service (QoS). In this study, we adapt a subtree-based technique to protect a multicast tree constructed for OpenFlow switches in SDN. The proposed algorithm can detect link or node failures from a multicast tree and then determines which part of the multicast tree requires changes in the flow table to recover from the failure. With a centralized controller in SDN, the backup paths can be created much more effectively in comparison to the signaling approach used in traditional multiprotocol label switching (MPLS) networks for backup paths, which makes the subtree-based protection mechanism feasible. We also implement a prototype of the algorithm in the POX controller and measure its performance by emulating failures in different tree topologies in Mininet.     

一种新的WDM网状网中的动态子通路保护算法

论文研究了业务量疏导WDM网状网中的生存性问题,提出一种新的基于优先级的自适用子通路保护算法(PASPP)。该算法在为子通路寻找保护通路时,高优先级业务可以通过抢占低优先级的业务保护通路来提高其连通率,而同时对低优先级业务也能提供部分保护。仿真结果表明,该算法有较好的性能。     

Efficient path protection in bi-directional WDM systems

Bi-directional WDM transmission is a technique that allows data to be transmitted simultaneously in both directions of a fiber, with different sets of wavelength channels for each direction. Compared with unidirectional WDM systems, it not only saves the cost of deploying extra fibers, but also allows more flexible bandwidth provisioning. To exploit this flexibility, we investigate path protection schemes for bi-directional WDM transmission systems in this paper. With path protection, a call is accepted if and only if an active data path together with a disjointed backup path can be found in the network. With bi-directional WDM, backup resource sharing in both directions of a fiber is possible. Based on a set of judiciously designed link cost functions, two original path protection schemes are proposed in this paper, BiPro and BiProLP. BiProLP aims at further economizing the hardware cost incurred by BiPro. In contrast to the traditional unidirectional schemes, we show that both BiPro and BiProLP can yield noticeably lower call blocking probability, higher system capacity and shorter active/backup path length.     

Restoration Probability Modelling for Active Restoration-Based Optical Networks with Correlation Among Backup Routes

Active restoration (AR) is a novel lightpath restoration scheme proposed recently to guarantee a certain degree of survivability in wavelength-division multiplexing (WDM) optical networks with a reasonable trade-off between capacity requirement and restoration time. In this paper, we conduct a comprehensive performance analysis for AR-based optical networks. In particular, we propose a novel analytical framework for modeling the restoration probability of a connection (the probability that the connection can be successfully restored in case of a failure) when the possible correlation among its multiple backup routes is incorporated. Although theoretically, we need to consider all the possible correlations between as many as Q) pairs of backup routes to analyze the restoration probability in a network with N nodes, and this high computation complexity may obscure the practicality of an approach, considering all the possible correlations among backup routes, our analysis in this paper indicates that by considering at most the possible correlations among any three successive backup routes of a connection, we can achieve a very good approximation to the simulated restoration probability of the connection, as verified by extensive simulation results upon two typical network topologies under various workloads. We find that the proposed framework can deeply investigate into the inherent relationship among restoration probability, wavelength channel utilization ratio, number of wavelengths per fiber, routes hop length, and wavelength conversion capability. As a result, the framework significantly contributes to the related areas by providing network designers with a quantitative tool to evaluate the restoration probability and, thus, the survivability of AR-based optical networks.     

Protecting multicast services in optical internet backbones

Many applications in the future Internet will use the multicasting service mode. Since many of these applications will generate large amounts of traffic, and since users expect a high level of service availability, it is important to provision multicasting sessions in the future Internet while also providing protection for multicast sessions against network component failures. In this paper we address the multicast survivability problem of using minimum resources to provision a multicast session and its protection paths (trees) against any single-link failure. We propose a new, and a resource efficient, protection scheme, namely, Segment-based Protection Tree (SPT). In SPT scheme, a given multicast session is first provisioned as a primary multicast tree, and then each segment on the primary tree is protected by a multicast tree instead of a path, as in most existing approaches. We also analyze the recovery performance of SPT and design a reconfiguration calculation algorithm to compute the average number of reconfigurations upon any link failure. By extending SPT to address dynamic traffic scenarios, we also propose two heuristic algorithms, Cost-based SPT (CB_SPT) and Wavelength-based SPT (WB_SPT). We study the performance of the SPT scheme in different traffic scenarios. The numerical results show that SPT outperforms the best existing approaches, optimal path-pair-based shared disjoint paths (OPP_SDPs). SPT uses less than 10% extra resources to provision a survivable multicast session over the optimal solution and up to 4% lower than existing approaches under various traffic scenarios and has an average number of reconfigurations 10–86% less than the best cost efficient approach. Moreover, in dynamic traffic cases, both CB_SPT and WB_SPT achieves overall blocking probability with 20% lower than OPP_SDP in most network scenarios.