Joint coverage and link utilization for fast IP local protection

To mitigate the impact of failures, many IP Fast Local Recovery (IPFLR) schemes have been proposed to reroute traffic in the events of failures. However, the existing IPFLR schemes either aimed to find the alternate backup routes to protect failures, or focused on balancing the traffic load routed on the backup routes. Furthermore, in Internet, flows are often managed by shortest path routing, and therefore purely determining the backup routing paths is not sufficient in protecting the error-prone networks. In this paper, we propose a Simulated Annealing based Load balancing and Protection (SALP) scheme to determine link weights for balancing link utilization in the non-failure state and simultaneously construct backup routing tables for protecting any single link failure in IP networks. In our proposed scheme, the two most significant issues, (1) load balancing and (2) coverage, are jointly considered to recover the network operation from single link failures. In the proposed scheme, upon a failure, only the nodes adjacent to a failure are activated to divert affected traffic to backup paths without disturbing regular traffic. Numerical results delineate that the proposed scheme achieves high coverage rate and load balancing at the expense of slightly increasing the entries of backup routing table.     

基于线性松弛方法的网络故障链路诊断

为解决通信网络中端到端测量定位故障链路的NP难问题,提出了一种新的松弛布尔约束的诊断方法。首先将网络中的路径状态和链路状态的关系建模为布尔代数方程,而故障定位的本质即满足该布尔方程条件的优化求解;然后,依据该优化表达式判断其NP性来源于链路状态的布尔约束（正常/故障）,通过将布尔约束松弛为线性约束,所提方法将问题简单地转换为线性规划（LP）问题,线性规划问题非常容易求解并可以由任何LP求解器来得到故障链路集合。在真实网络拓扑中进行了链路故障诊断仿真实验,实验结果表明,所提方法与现有的经典启发式算法——TOMO相比,降低了5%~30%的误诊率。     

Inter-Cluster Routing Authentication for Ad Hoc Networks by a Hierarchical Key Scheme

Dissimilar to traditional networks, the features of mobile wireless devices that can actively form a network without any infrastructure mean that mobile ad hoc networks frequently display partition due to node mobility or link failures. These indicate that an ad hoc network is difficult to provide ou-llne access to a trusted authority server. Therefore, applying traditional Public Key Infrastructure （PKI） security framework to mobile ad hoc networks will cause insecurities. This study proposes a scalable and elastic key management scheme integrated into Cluster Based Secure Routing Protocol （CBSRP） to enhance security and non-repudiation of routing authentication, and introduces an ID-Based internal routing authentication scheme to enhance the routing performance in an internal cluster. Additionally, a method of performing routing authentication between internal and external clusters, as well as inter-cluster routing authentication, is developed. The proposed cluster-based key management scheme distributes trust to an aggregation of cluster heads using a threshold scheme faculty, provides Certificate Authority （CA） with a fault tolerance mechanism to prevent a single point of compromise or failure, and saves CA large repositories from maintaining member certificates, making ad hoc networks robust to malicious behaviors and suitable for numerous mobile devices.     

Reliable multistage interconnection network design

High-performance supercomputers generally comprise millions of CPUs in which interconnection networks play an important role to achieve high performance. New design paradigms of dynamic on-chip interconnection network involve a) topology b) synthesis, modeling and evaluation c) quality of service, fault tolerance and reliability d) routing procedures. To construct a dynamic highly fault tolerant interconnection networks requires more disjoint paths from each source-destination node pair at each stage and dynamic rerouting capability to use the various available paths effectively. Fast routing and rerouting strategy is needed to provide reliable performance on switch/link failures. This paper proposes two new architecture designs of fault tolerant interconnection networks named as reliable interconnection networks (RIN-1 and RIN-2). The proposed layouts are multipath multi-stage interconnection networks providing four disjoint paths for all the source-destination node pairs with dynamic rerouting capability. The designs can withstand switch failures in all the stages (including input and output stages) and provide more reliability. Reliability analysis of various MIN architectures is evaluated. On comparing the results with some existing MINs it is evident that the proposed designs provides higher reliability values and fault tolerance.     

Design of 4-disjoint gamma interconnection network layouts and reliability analysis of gamma interconnection Networks

Multistage interconnection networks (MINs) are widely used for reliable data communication in a tightly coupled large-scale multiprocessor system. High reliability of MINs can be achieved using fault tolerance techniques. The fault tolerance is generally achieved by disjoint paths available through multiple connectivity options. The gamma interconnection network (GIN) is a class of fault tolerant MINs providing alternate paths for source–destination node pairs. Various 2-disjoint and 3-disjoint GIN architectures have been presented in the literature. In this paper, two new designs of 4-disjoint paths multistage interconnection networks, called 4-disjoint gamma interconnection networks (4DGIN-1 and 4DGIN-2) are proposed. The proposed 4DGINs provide four disjoint paths for each source–destination pair and can tolerate three switches/link failures in intermediate interconnection layers. Proposed designs are highly reliable GIN with higher fault-tolerant capability than other gamma networks at low cost. Terminal pair reliabilities of proposed designs and various other 2-disjoint and 3-disjoint GINs are evaluated, analyzed and compared. Reliability values of proposed designs are found higher.     

Multidomain Diagnosis of End-to-End Service Failures in Hierarchically Routed Networks

Probabilistic inference was shown effective in the nondeterministic diagnosis of end-to-end service failures when applied in a centralized management system where the manager possesses a global knowledge of the system structure and state. Since many networks are organized into multiple administrative domains that may be unable to share configuration and state information, these centralized techniques are not applicable to them. This paper proposes a fault localization technique suitable for multidomain networks with hierarchical routing. The proposed technique divides the computational effort and system knowledge among multiple, hierarchically organized managers. Each manager performs fault localization in the domain it manages and requires only the knowledge of its own domain. We show through simulation that the proposed approach not only improves the feasibility of fault localization in multidomain networks, but also increases the effectiveness of probabilistic diagnosis and makes it realizable in networks of considerable size     

基于拥塞及内存感知的SD-WAN故障恢复

在软件定义广域网(SD-WAN)中, 链路故障会导致大量丢包, 严重时会引起部分网络瘫痪. 现有的流量工程方法通过在数据平面提前安装备份路径能够加快故障恢复过程, 但在资源受限的情况下难以适应各种网络故障情况, 从而使恢复后的网络性能下降. 为了保证网络在故障恢复之后的性能并减少备份资源的消耗, 本文提出一种基于拥塞及内存感知的主动式故障恢复方案(CAMA), 不仅能够将受影响数据流进行快速重定向, 还能实现负载均衡避免恢复后潜在的链路拥塞. 实验结果表明, 与已有方案相比, CAMA能有效利用备份资源, 在负载均衡上有较好的性能, 且仅需少量备份规则即可覆盖所有单链路故障情况.     

Using Network Fault Predictions to Enable IP Traffic Management

IP traffic management is important for the continued growth of the Internet. Several traffic management algorithms exist today. However, to enable these algorithms it is necessary to provide reliable alarms relating to network performance bottlenecks and failures. In this work we propose an algorithm to obtain reliable predictive alarms for network fault conditions. The algorithm is based on modeling network fault behavior. The algorithm has been successfully tested on two production networks. Predictive alarms were obtained for four different types of failures: file server failures, network access problems, protocol implementation errors, and runaway processes. The potential of using this model to do fault classification is also discussed. In addition, it is shown that the proposed algorithm performs better than the majority-vote scheme.     

Dynamic Path Management with Resilience Constraints under Multiple Link Failures in MPLS/GMPLS Networks

Most previous research on MPLS/GMPLS recovery management has focused on efficient routing or signaling methods from single failures. However, multiple simultaneous failures may occur in large-scale complex virtual paths of MPLS/GMPLS networks. In this paper, we present a dynamic MPLS/GMPLS path management strategy in which the path recovery mechanism can rapidly find an optimal backup path which satisfies the resilience constraints under multiple link failure occurrences. We derived the conditions to test the existence of resilience-guaranteed backup path, and developed a decomposition theorem and backup path construction algorithm for the fast restoration of resilience-guaranteed backup paths, for the primary path with an arbitrary configuration. Finally, simulation results are presented to evaluate the performance of the proposed approach.     

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.     

Secure and efficient key management in mobile ad hoc networks

In mobile ad hoc networks, due to unreliable wireless media, host mobility and lack of infrastructure, providing secure communications is a big challenge. Usually, cryptographic techniques are used for secure communications in wired and wireless networks. Symmetric and asymmetric cryptography have their advantages and disadvantages. In fact, any cryptographic means is ineffective if its key management is weak. Key management is also a central aspect for security in mobile ad hoc networks. In mobile ad hoc networks, the computational load and complexity for key management are strongly subject to restriction by the node's available resources and the dynamic nature of network topology. We propose a secure and efficient key management (SEKM) framework for mobile ad hoc networks. SEKM builds a public key infrastructure (PKI) by applying a secret sharing scheme and using an underlying multi-cast server groups. We give detailed information on the formation and maintenance of the server groups. In SEKM, each server group creates a view of the certificate authority (CA) and provides certificate update service for all nodes, including the servers themselves. A ticket scheme is introduced for efficient certificate service. In addition, an efficient server group updating scheme is proposed. The performance of SEKM is evaluated through simulation.     

基于优化链路权值的域内路由保护方案

目前,互联网部署的域内链路状态路由协议,如开放最短路径优先(Open Shortest Path First,OSPF)和中间系统到中间系统(Intermediate System-to-Intermediate System,IS-IS),采用被动恢复方案应对网络故障。随着网络的发展,大量的实时应用部署在互联网上,OSPF的收敛时间无法满足这些实时应用对收敛时间的需求。因此,学术界和工业界提出采用路由保护方案来应对网路中出现的故障。然而,已有的路由保护方案存在两个方面的问题:1)默认路径和备份路径的交叉度较高,如LFA；2)为了计算两条交叉度低的路径,对默认路径加以限制,即默认路径不采用最短路径,如Color Tree。为了解决上述两个问题,首先将上述问题归结为整数规划模型,接着利用启发式方法计算近似最优解,最后在实际网络和模拟网络中对所提算法进行了大量实验。实验结果表明,所提算法可以降低默认路径和备份路径的交叉度,极大地提高网络的可用性。     

A new algorithm for virtual path network design in ATM networks

Virtual paths (VPs) in an ATM network form a logical network, called VP network (VPN), over the underlying physical network. VPN allows flexible management of network resources and hence its design is an important issue in designing an ATM network. In this paper, we consider the VPN design problem which is formulated as an optimization problem with the objective of minimizing the switching and transmission cost, and control and management cost. We present here, a two-phase heuristic solution for designing a good VPN for a given traffic demand. The first phase is a routing phase in which a route is found between every node pair in the network. In the second phase, paths are selected as VPs using the set of routes generated in the routing phase. A path is selected as a VP so as to minimize the following parameters: (i) the total number of VPs configured; (ii) the number of VPs carried by a link (load); and (iii) the VP hopcount, the number of VPs that are concatenated to form a virtual channel (VC). We study the performance of the proposed algorithm through extensive simulation on various networks. The results show that the VPN generated by the proposed algorithm is good in minimizing the number of VPs configured, the load on a link, and the VP hopcount. The comparison of the results obtained by the proposed algorithm and that of Ahn et al. [Virtual path layout design in ATM networks, in: Proceedings of IEEE INFCOM’94, Toronto, Ontario, Canada, 1994, pp. 192–200] shows that our algorithm performs better.     

Intra-domain routing convergence with centralized control

The decentralized control scheme for routing in current IP networks has been questioned, and a centralized routing scheme has been proposed as an alternative. In this paper, we compare the convergence of centralized control scheme with decentralized link-state routing protocols. We first review the architectural advantages and challenges of centralized control. Thereafter, we identify and discuss the components of the convergence time in both schemes. We present how to achieve fast routing convergence in networks with centralized control. In particular, we analyze how to distribute forwarding information efficiently. Finally, we perform simulation studies on the convergence time for both real and synthetic network topologies and study the impact of control element location, link weights, and number of failures on the convergence time. The results show that the centralized control scheme can provide faster routing convergence than link-state routing protocols.     

多信道无线Mesh网络信道分配算法

针对无线Mesh网络的带宽容量问题,文章通过使用无线网络干扰协议模型对无线链路的干扰进行量化,利用整数线性规划公式对信道分配问题进行描述,在信道分配的时候,应用目标函数对无线链路的信道分配进行优化,使网络总的干扰权重最小化,在此基础上提出一个信道分配的启发式算法。仿真结果表明,文章提出的算法能提高网络的吞吐量。     

多信道无线Mesh网络负载均衡路由算法研究

针对无线网状网的网络容量问题,在多信道无线网状网模型的基础上,利用线性规划公式对无线网状网的路由问题进行描述,在此基础上提出了一个负载均衡的路由算法,在对业务请求的路由跳步数进行约束的前提上,通过减少网络链路上的负载,达到提高网络的吞吐量的目的。仿真结果表明,提出的算法能显著提高网络性能。     

视频服务器网络中影像对象映射问题的研究

视频服务器网络中的影像对象映射问题是一种新的组合优化问题.服务器网络可以建立在基于局域网的工作站网络之上,也可以建立在广域网之上.基于对用户的服务请求模式、服务器网络的存储容量和通信带宽等因素的综合考虑,研究了服务器网络中影像对象映射问题,利用局部搜索算法给出了一套对该映射问题的解决方案.然后用一套基准集实例对给出的算法集进行验证.结果表明,在较短的计算时间内,该算法可以得到近似最优解的方案.     

Segment Routing体系结构中的域内路由保护方案

学术界和工业界提出利用路由保护方案来提高域内路由协议应对故障的能力，从而加速网络故障恢复，降低由于网络故障引起的网络中断时间。目前互联网普遍采用的路由保护方案包括LFA和U-turn，由于它们的简单和高效，受到了互联网服务提供商的支持，但是这两种方案的单链路故障保护率较低。因此，段路由（Segment Routing，SR）被提出解决上述两种方案存在的问题，已有的针对SR的研究主要集中在其体系结构和应用场景。研究如何在SR中计算segments，将该问题表述为一个整数线性规划问题，提出一种两阶段的启发式算法（Two Phase Heuristic Algorithm，TPHA）求解该问题，将算法在不同网络拓扑中进行了模拟。模拟结果表明，TPHA的单链路故障保护率远远高于LFA和U-turn的单链路故障保护率。     

Redundant multicast routing in multilayer networks with shared risk resource groups: Complexity,models and algorithms

This paper presents a redundant multicast routing problem in multilayer networks that arises from large-scale distribution of realtime multicast data (e.g., Internet TV, videocasting, online games, stock quotes). Since these multicast services commonly operate in multilayer networks, the communications paths need to be robust against a single router or link failure as well as multiple such failures due to shared risk link groups (SRLGs). The main challenge of this multicast is to ensure the service availability and reliability using a path protection scheme, which is to find a redundant path that is SRLG-disjoint (diverse) from each working path. The objective of this problem is, therefore, to find two redundant multicast trees, each from one of the two redundant sources to every destination, at a minimum total communication cost whereas two paths from the two sources to every destination are guaranteed to be SRLG-diverse (i.e., links in the same risk group are disjoint). In this paper, we present two new mathematical programming models, edge-based and path-based, for the redundant multicast routing problem with SRLG-diverse constraints. Because the number of paths in path-based model grows exponentially with the network size, it is impossible to enumerate all possible paths in real life networks. We develop three approaches (probabilistic, non-dominated and nearly non-dominated) to generate potentially good paths that may be included in the path-based model. This study is motivated by emerging applications of internet-protocol TV service, and we evaluate the proposed approaches using real life network topologies. Our empirical results suggest that both models perform very well, and the nearly non-dominated path approach outperforms all other path generation approaches.     

A Dynamic Shadow Approach to Fault-Tolerant Mobile Agents in an Autonomic Environment

Large-scale distributed applications such as online information retrieval and collaboration over computational elements demand an approach to self-managed computing systems with a minimum of human interference. However, large scales and full distribution often lead to poor system dependability and security, and increase the difficulty in managing and controlling redundancy for fault tolerance. In particular, fault tolerance schemes for mobile agents to survive agent server crash failures in an autonomie environment are complex since developers normally have no control over remote agent servers. Some solutions inject a replica into stable storage upon its arrival at an agent server. But in the event of an agent server crash the replica is unavailable until the agent server recovers. In this paper we present a failure model and an exception handling framework for mobile agent systems. An exception handling scheme is developed for mobile agents to survive agent server crash failures. A replica mobile agent operates at the agent server visited prior to its master's current location. If a master crashes its replica is available as a replacement. The proposed scheme is examined in comparison with a simple time-out scheme. Experimental evaluation is performed, and performance results show that the scheme leads to some overhead in the round trip time when fault tolerance measures are exercised. However the scheme offers the advantage that fault tolerance is provided during the mobile agent trip, i.e. in the event of an agent server crash all agent servers are not revisited.