A novel path protection scheme for MPLS networks using multi-path routing

Multi-protocol label switching (MPLS) is an evolving network technology that is used to provide traffic engineering (TE) and high speed networking. Internet service providers, which support MPLS technology, are increasingly demanded to provide high quality of service (QoS) guarantees. One of the aspects of QoS is fault tolerance. It is defined as the property of a system to continue operating in the event of failure of some of its parts. Fault tolerance techniques are very useful to maintain the survivability of the network by recovering from failure within acceptable delay and minimum packet loss while efficiently utilizing network resources.In this paper, we propose a novel approach for fault tolerance in MPLS networks. Our approach uses a modified (k, n) threshold sharing scheme with multi-path routing. An IP packet entering MPLS network is partitioned into n MPLS packets, which are assigned to node/link disjoint LSPs across the MPLS network. Receiving MPLS packets from k out of n LSPs are sufficient to reconstruct the original IP packet. The approach introduces no packet loss and no recovery delay while requiring reasonable redundant bandwidth. In addition, it can easily handle single and multiple path failures.     

A New Fast Backup Method for Bidirectional Multicast Traffic in MPLS Networks: Control Plane Procedures and Evaluation by Simulations

Bidirectional multicast mechanisms are used to support multi-point to multi-point (MP2MP) traffic such as video-conferencing. These mechanisms are deployed today in multi-protocol label switching (MPLS) networks using the connectionless mode in which traffic engineering (TE) features such as bandwidth reservation and fast reroute in case of link and/or node failure are not defined. Indeed, TE procedures are defined in MPLS for unicast and multicast point-to-multipoint (P2MP) traffic only. Hence, MP2MP traffic that requires TE procedures is carried out using a full mesh of P2P or P2MP paths. Similarly, a full mesh of P2P and P2MP backup paths should be predefined in order to fast reroute traffic in case of a node failure. This leads to a major scalability problem since MPLS TE paths incur heavy overhead burden on MPLS nodes (CPU and memory). In this paper, we emphasize on fast reroute procedures using MP2MP TE paths. In particular, we define the control plane procedures that should be established. In addition, we present a simulation study that demonstrates the scalability amelioration when using MP2MP TE paths for fast rerouting instead of full mesh P2P and/or P2MP paths.     

Fast setup of end-to-end paths for bandwidth constrained applications in an IP/MPLS–ATM integrated environment

Transport networks are currently being moved towards a model of high performance Internet Protocol/Multiprotocol Label Switching (IP/MPLS) routers interconnected through intelligent core networks. Currently, Asynchronous Transfer Mode (ATM) technology has been widely deployed in several network backbones along with the Private Network-to-Network Interface (PNNI) protocols as the control plane. In order to cope with the increasing Internet traffic demands in the current context, fast setup of end-to-end paths with the required Quality of Service (QoS) is necessary.This paper analyzes the case of two IP/MPLS networks interconnected through an ATM core network, assuming MPLS as the mechanism to provide Traffic Engineering in the IP networks, and a PNNI-based control plane in the core network. This paper aims to define a mechanism needed to set up a fast end-to-end QoS Label Switched Path (LSP) between two Label Switched Routers (LSRs) belonging to different IP/MPLS domains. First, the fast end-to-end setup is achieved by modifying the network backbone control plane. Second, two different aggregation schemes are proposed to summarize the QoS network state information to be transported through the ATM core network. Therefore, both the efficient aggregation schemes and the fast mechanism allow source routing to set up a path faster than the existing methods and to reduce the blocking probability using a summary of the available resource information.     

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.     

Loop-free alternates and not-via addresses: A proper combination for IP fast reroute?

The IETF currently discusses fast reroute mechanisms for IP networks (IP FRR). IP FRR accelerates the recovery in case of network element failures and avoids micro-loops during re-convergence. Several mechanisms are proposed. Loop-free alternates (LFAs) are simple but cannot cover all single link and node failures. Not-via addresses can protect against these failures but are more complex, in particular, they use tunneling techniques to deviate backup traffic. In the IETF it has been proposed to combine both mechanisms to merge their advantages: simplicity and full failure coverage.This work analyzes LFAs and classifies them according to their abilities. We qualitatively compare LFAs and not-via addresses and develop a concept for their combined application to achieve 100% single failure coverage, while using simple LFAs wherever possible. The applicability of existing LFAs depends on the resilience requirements of the network. We study the backup path length and the link utilization for both IP FRR methods and quantify the decapsulation load and the increase of the routing table size caused by not-via addresses. We conclude that the combined usage of both methods has no advantage compared to the application of not-via addresses only.     

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.     

MPLS快速重路由多故障恢复算法的研究

传统的MPLS快速重路由技术在面对网络多故障的情况时有许多不足之处,为了更好的解决问题,提出一种新的MPLS快速重路由多故障恢复算法.算法采用Detour路径保护方式,对有不同备份路径经过的链路上的预留带宽资源进行共享管理,并为工作路径建立主、从备份路径.仿真实验结果显示,该算法能够有效减少备份路径上预留带宽资源消耗,对出现多故障的网络进行快速恢复.     

MPLS技术及其发展趋势

多协议标签交换使用定长的标签来引导数据高速传输和交换。MPLS,实现了增强的流量工程和负载均衡,为服务供应商和企业改善整体网络管理、更好地利用可用带宽提供了技术支持。MPLS技术为传输网和光网络、支持移动IP、以及在无线移动通信网的发展中提供了重要解决方案     

Multiprotocol label switching and IP. Part I. MPLS VPNs over IP tunnels

Multiprotocol label switching (MPLS) is a tunneling technology used in many service provider networks. The most popular MPLS-enabled application in use today is the MPLS virtual private network, MPLS VPNs were developed to operate over MPLS networks, but they can also run over native IP networks. This offers providers flexibility in network-deployment choices, improved routing system scalability, and greater reach to customers. The key element is the ability to encapsulate MPLS packets in IP tunnels.     

支持多故障恢复的MPLS快速重路由

分析了传统MPLS快速重路由应对多故障环境的不足,提出一种支持MPLS域并发多故障时快速恢复的重路由策略.通过有限洪泛故障信息,使本地修复的节点掌握有限范围内节点、链路的可用性信息,并通过建立主,从备份路径,保证MPLS层有效的恢复及较快的切换速度.理论分析及实验结果表明了该方法的可行性和有效性.     

基于VRF和RT实现BGP／MPLS VPNs中的VPN拓扑发现

在RFC 2547中定义的BGP／MPLS VPNs允许服务提供者使用他们的IP骨干提供VPN服务，使用BGP对骨干网络的路由器分发VPN路由信息，使用MPLS转发VPN流量。BGP／MPLS VPNs允许服务提供者在VPN内定义拥有任意数量结点的任意拓扑。服务提供者能建立使用相同核心网络的多个VPN。目前大多数服务提供者手工地或通过使用配置的数据库实现BGP／MPLS VPNs。本文描述的算法使VPN拓扑发现过程自动化。使用该算法，服务提供者能使用当前网络配置信息自动地发现VPN拓扑。     

汇聚组播:新型MPLS服务质量组播体系结构

为支持新兴网络应用,IP组播(multicast)和MPLS(multi-protocol label switching)技术分别从不同方向扩展了当前的IP路由和交换模式.MPLS和IP组播的结合是当前研究的一个热点,MPLS网络中的服务质量组播面临着标签资源匮乏、组播路由状态的可扩展性以及具体实现上的困难.针对这些问题,提出了基于汇聚方法的新型MPLS服务质量组播体系结构,提出在现有的路由控制平面上叠加一层面向IP组播服务的控制平面,取代组播路由协议并支持组播聚集,形成2层控制平面结构.定义了两平面之间的协作和交互方式,并通过扩展RSVP-TE(resource reservation protocol-traffic engineering) P2MP(point to multi-point)协议,在新的体系结构中融合了服务质量控制能力.另外,还探讨了汇聚组播中基于距离约束选择汇聚路由器的算法,实现了基于Linux的MPLS组播路由器和IP组播服务控制系统,并组建了实验平台.实验和模拟结果表明,基于汇聚组播的双平面网络控制结构能够适应组播用户和网络拓扑的动态变化,能够有效节省MPLS标签资源,平衡网络中组播流量的分布.     

Designing a Reliable IPTV Network

Meeting IPTV's quality of service constraints (such as low latency and loss) requires designing the right combination of underlying IP-transport, restoration, and video and packet recovery methods. Carriers use link-based fast reroute (FRR) as the primary transport restoration method to achieve this goal. Although we can carefully tune the link weights in the IP routing protocol to avoid traffic overlap from FRR during single link failures, multiple failures can still cause path overlap in long-distance networks. By having FRR, IGP, and multicast protocols work in harmony and with appropriate link weight assignments, this approach can help minimize path overlap during multiple failures.     

Layer 2 over IP/MPLS

Over the past several years, traditional carriers and Internet service providers (ISPs) have invested billions of dollars deploying high-speed, high-capacity IP networks. This expansion is intended to lay the foundation for a network that could accommodate exponential traffic growth and deliver new revenue-generating services. Traffic from advanced services incorporating elements such as on-demand video, packet voice, wireless communications, and peer-to-peer networking is expected to consume whatever capacity providers can offer while leading to increased opportunities for revenue growth. The advanced services traffic has yet to materialize. An unintentional consequence of this buildout, however, is that ISP networks possess a glut of capacity. At the same time, ISPs are under great pressure to reduce operational and infrastructure costs while attempting to make money and attract customers with new services. One way to achieve both goals is to carry all traffic over a single IP or multiprotocol label-switching (MPLS) network     

Extension of Multiprotocol Label Switching for long-range dependent traffic: QoS routing and performance in IP networks

This paper presents an extension to the Multiprotocol Label Switching (MPLS) traffic engineering in IP networks with long-range dependent traffic. The extension provides the ability to diverge traffic flows away from the shortest path calculated by the traditional IP routing protocols into a less congested area of the network. When the traffic burstiness of a packet flow exceeds a predefined threshold, the extension calculates the cost of the traffic distribution and the effectiveness of Label Switching Routers (LSPs) to minimize the number of discarded packets. The simulation results demonstrate that the extension significantly improves the overall network performance in link utilization, port processor utilization, message delay, number of dropped packets, and buffer usage level.     

Policy-Based Grooming in Optical Networks

This work presents a discussion about policies and architecture to aggregate Internet Protocol/Multiprotocol Label Switching (IP/MPLS) traffics within lightpaths. The scenario is that of IP/MPLS client networks over an optical network. It is well known that aggregating lower traffic flows (e.g., packet-based LSPs—Label Switched Path) within higher traffic flows (e.g., lambda-based LSPs) is considered an effective way to maximize the use of the optical network resources. In this work, the policies are divided into two groups. The first one, which solely considers the class of the flow (High Priority—HP or Low Priority—LP), consists of simple policies meant to aggregate packet-based LSPs within lightpaths. In this group, the policies we have defined intend to reduce the optical network overhead to remove and reroute LP LSPs. The second group presents more sophisticated policies taking into account the possibility of having to deal with further transport faults. In this case, the grooming is better planned and the defined policies tend to reduce the negative impact when a failure is detected in the optical transport network. Our approach has been implemented to validate the policies and the results for each group are showed and discussed.     

一种快捷的MPLS网络负载均衡动态路由算法

针对MPLS网络引入了一种快捷的有带宽保证的负载均衡动态路由算法（FDRA）,该算法通过提出预期负载的概念和链路上的剩余容量来定义链路的成本,然后采用以链路成本为基础的最短路径算法选路,使得网络快捷地建立尽可能多的有带宽保证的路由,并且使这些路由均衡地通过网络。在与其他算法相比较中,该算法在业务请求拒绝率和重路由性能方面有更好的表现,特别是路由的建立时间快捷。     

New MPLS network management techniques based on adaptive learning

The combined use of the differentiated services (DiffServ) and multiprotocol label switching (MPLS) technologies is envisioned to provide guaranteed quality of service (QoS) for multimedia traffic in IP networks, while effectively using network resources. These networks need to be managed adaptively to cope with the changing network conditions and provide satisfactory QoS. An efficient strategy is to map the traffic from different DiffServ classes of service on separate label switched paths (LSPs), which leads to distinct layers of MPLS networks corresponding to each DiffServ class. In this paper, three aspects of the management of such a layered MPLS network are discussed. In particular, an optimal technique for the setup of LSPs, capacity allocation of the LSPs and LSP routing are presented. The presented techniques are based on measurement of the network state to adapt the network configuration to changing traffic conditions.     

On basic properties of fault-tolerant multi-topology routing

Multi-topology routing has recently gained popularity as a simple yet efficient traffic engineering concept. Its basic purpose is to separate different classes of network traffic, which are then transported over disjoint logical topologies. Multi-topology routing is used as a basis for implementation of an IP fast reroute scheme called Multiple Routing Configurations (MRC).MRC has a range of attractive properties, but they do come at a cost. In order to guarantee recovery from any single link or node failure in the network, MRC has to maintain several logical topologies and thus an increased amount of routing information. The number of the logical topologies in MRC need not be large; even simple heuristic algorithms often yield good results in practice. However, why this is the case is not fully understood yet.In this paper, we introduce a theoretical framework for fault-tolerant multi-topology routing (FT-MTR). MRC is a practical implementation of FT-MTR in connectionless IP networks. We use FT-MTR to study how the internal topological structure of the communication network relates to two important problems. The first problem is minimizing the number of logical topologies and thus the routing state in FT-MTR. We show how to use the sets of nodes that separate the topology graph to devise an advanced heuristic for “intelligent” construction of the logical topologies. Finding the separating sets in a topology graph is computationally demanding; we present an algorithm that performs well in tested real network topologies. We evaluate the separation-set based heuristic for the logical topology construction and show that it outperforms the known MRC heuristics.The second problem is the FT-MTR load distribution after a failure. We use the separating sets to devise a novel algorithm for failure load distribution. This algorithm does not require knowledge of the traffic demand matrix, still, our tests indicate that it performs as good as, or better than, known MRC load-distribution algorithms that do require the demand matrix as input.     

Energy-aware traffic engineering: A routing-based distributed solution for connection-oriented IP networks

The present paper deals with energy saving in IP networks and proposes a distributed energy-aware traffic engineering solution, named DAISIES, for switching off network links according to traffic variations. DAISIES works in a connection-oriented network, e.g. an IP/MPLS network, and follows a routing-based approach, i.e. it acts on the routing algorithm whilst link switch-off/on are consequence of routing decisions. The basic idea is to re-compute the path of each traffic demand when its requested capacity changes. A specific cost function is used to compute link weights into the shortest path routing algorithm with the goal of keeping unused as many links as possible. The main advantages of DAISIES can be summarized as follows: (i) no changes are required to current routing and signaling protocols, (ii) packet loss is completely avoided, (iii) both traffic decreasing and increasing and changing network conditions are automatically managed, and (iv) link switch-off/on take place transparently to the routing protocol and to other nodes. The performance of the proposed solution is evaluated in terms of energy saving relative to a static network optimized to support the peak traffic. Results show that DAISIES is able to save about 30% of energy in several traffic conditions. Moreover, it is shown that it is possible keeping the additional complexity low and still reaching high energy efficiency.