On failure dependent protection in optical grooming networks

In this paper, we study the impact of shared risk link group (SRLG) failures on shared-path protection by examining the percentage of connections that are vulnerable after SRLG failures, investigate the benefits of backup reprovisioning after SRLG failures, and evaluate different policies for backup reprovisioning. Compared with single-link failures, SRLG failures leave many more connections unprotected and vulnerable to the next failures and make the network topology much sparser. The major challenge of backup reprovisioning after SRLG failures is how to find SRLG-disjoint backup paths for those unprotected connections with a recovery ratio that is as high as possible within reasonable computational complexity. We are motivated to consider three reprovisioning policies by considering different sequences of reprovisioning according to the degree of SRLG constraints. The first policy is to reprovision backup paths for connections whose working paths traverse more SRLGs first (Policy I), and the second policy is to reprovision backup paths for connections whose working paths traverse fewer SRLGs first (Policy II). The third policy is to do backup reprovisioning randomly, i.e., we pick up an unprotected working path randomly (random reprovisioning). Extensive simulation results show that 1) SRLG failures will leave more connections unprotected compared with single-link failures, and the percentage of connections left vulnerable tends to be proportional to the SRLG size; 2) the network performance based on the first reprovisioning policy always performs best in recovery ratio; and 3) the network performance based on Policy II even underperforms the random reprovisioning. These results can be explained by the fact that connections whose working paths traverse fewer SRLGs are more flexible in finding SRLG-disjoint backup paths, and thus priority given to connections whose working paths traverse more SRLGs in Policy I can significantly improve the recovery ratio.

Link failures in wide area networks are common. To recover from such failures, a number of methods such as SONET rings, protection cycles, and source rerouting have been investigated. Two important considerations in such approaches are the recovery time and the needed spare capacity to complete the recovery. Usually, these techniques attempt to achieve a recovery time less than 50 ms. In this paper we introduce an approach that provides link failure recovery in a hitless manner, or without any appreciable delay. This is achieved by means of a method called diversity coding. We present an algorithm for the design of an overlay network to achieve recovery from single link failures in arbitrary networks via diversity coding. This algorithm is designed to minimize spare capacity for recovery. We compare the recovery time and spare capacity performance of this algorithm against conventional techniques in terms of recovery time, spare capacity, and a joint metric called Quality of Recovery (QoR). QoR incorporates both the spare capacity percentages and worst case recovery times. Based on these results, we conclude that the proposed technique provides much shorter recovery times while achieving similar extra capacity, or better QoR performance overall.

We consider routing in survivable networks that provide protection against node or link failures. In these networks resilience against failures is provided by routing connections on pairs of disjoint paths called primary and backup paths. The primary path of a connection carries its traffic under normal circumstances and in the eventuality of a network failure effecting the primary path the connection traffic (all or some portion of it) is rerouted over its backup path. In an online setting as connection requests arrive a pair of disjoint primary and backup paths of least total cost (under some link cost metric) are selected to route the connections. In many situations the cost metric used for the primary path differs from the cost metric used for the backup path. Also in many realistic settings these two cost metrics are related to each other. In this paper we study the problem of finding a pair of edge or node disjoint paths of least total cost where the cost of the primary path is the total cost of its links while the cost for the backup path is α times the sum of the cost of its links, for some given α < 1. We show that the problem is hard to approximate to within a factor $$\Omega((\frac{1}{\alpha})^{1-\epsilon})$$ for any positive $$\epsilon \le 1$$ . In addition we show that the problem is complete for a set of hard to approximate problems. On the positive side we show that a simple algorithm achieves an approximation ratio of $$O(\frac{1}{\alpha})$$ for the problem.

An efficient critical protection scheme for intra-domain routing using link characteristics

The paper proposes a Fast ReRoute model with the realization of path and bandwidth protection scheme, which can be used in MPLS for SDN. The task of calculating the set of disjoint primary and backup paths during fast rerouting was reduced to solving the optimization problem of Integer Linear Programming. The advantage of the proposed solution is the possibility of implementing 1:1, 1:2, …, 1:n path protection schemes without the introduction of an additional set of control (routing) variables, which contributes to reducing the dimension of the optimization problem being solved and the computational complexity of its practical implementation. The criterion of optimality of routing solutions contributes to the formation of the primary and backup disjoint paths with the highest possible bandwidth. In this case, the path with the maximum bandwidth will correspond to the primary path, while the remaining paths will be used as backup ones in decreasing order of their bandwidth. The total number of calculated disjoint paths depends on the selected redundancy scheme. The study conducted showed the efficiency and adequacy of the proposed Fast ReRoute model when using various redundancy schemes.

Due to the high data rates in optical networks,physical-layer attacks targeting service degradation, such as powerjamming, can potentially lead to large data and revenue losses.Conventional network survivability approaches which establishlink-disjoint working and backup paths to protect from componentfaults may not provide adequate protection for such attacks.Namely, the working and the backup paths, although link-disjoint,might both be affected by a single attack scenario due to specificattack propagation characteristics. To enhance the existing survivabilityapproaches, we utilize the concept of an attack group(AG) which incorporates these characteristics to identify connectionswhich can simultaneously be affected by a single attack. Weapply this concept to dedicated path protection (DPP) and developattack-aware DPP (AA-DPP) approaches which aim to establishAG-disjoint primary and backup paths in a cost-effective manner.We provide a two-step ILP formulation for the routing and wavelengthassignment of the working and backup paths, as well as aheuristic for larger problem instances. Numerical results indicatethat the proposed approaches provide dedicated path protectionschemes with enhanced attack protection without using more resources(i.e., wavelengths, average path lengths) than standardDPPmethods.

Distributed sub-light-tree based multicast provisioning with shared protection in elastic optical datacenter networks

A failure in optical networks can cause tremendous loss in data and revenue. To guarantee the service availability and handle network failures, shared protection is commonly used. One promising shared protection approach has been proposed which introduce relative priorities among connections contending for access to the shared backup paths. In this paper, a novel priority-aware shared protection algorithm is developed, called FPS, for the dynamic connection provision. In FPS, the relative priority between an incoming connection and an existing connection is flexibly determined to maximize the usage of backup wavelengths after ensuring not to violate the SLA-defined availability requirement of the existing connection. We show that the FPS can obtain significant improvements on resource overbuilding ration and blocking probability compared with existing priority-aware shared protection algorithm.

Routing and wavelength assignment vs. EDFA reliability performance in optical backbone networks: An operational cost perspective

Fast-recovery from link failures is a well-studied topic in IP networks. Employing fast-recovery in Ethernet networks is complicated as the forwarding is based on destination MAC addresses, which do not have the hierarchical nature similar to those exhibited in Layer 3 in the form of IP-prefixes. Moreover, switches employ backward learning to populate the forwarding table entries. Thus, any fast recovery mechanism in Ethernet networks must be based on undirected spanning trees if backward learning is to be retained. In this paper, we develop three alternatives for achieving fast recovery from single link failures in Ethernet networks. All three approaches provide guaranteed recovery from single link failures. The approaches differ in the technologies required for achieving fast recovery, namely VLAN rewrite or mac-in-mac encapsulation or both. We study the performance of the approaches developed on five different networks.

We propose a rapid restoration strategy against PNE-node failure during post-disaster cooperation among DC providers and optical-network carriers. Our strategy reduces disruption and improves DC-service restoration by 35% in 20% less time compared to baseline.

Partitioning a large network into a connected hierarchy is a proven technique for scalability, manageability, and reliability. Although a significant body of works is devoted to this area of interest, a reference to partitioning schemes where each partition remains 2-connected is missing. In optical networks, a failure of a physical component disrupts multiple logical links that share the component. Such a shared risk link group (SRLG) failure is more common than a single link or node failure in the logical topology. In this paper, we introduce the k-SRLG-connected partitioning problem for optical networks, where k ≥ 1. A logical topology is said to be k-SRLG-connected if its nodes remain connected upon any k-1 SRLG failures. We particularly focus on k = 2. Without 2-SRLG-connectivity, a partition can neither provide protection by allocating two SRLG-disjoint paths, nor provide restoration after a failure. Moreover, a single SRLG failure can split the partition into multiple disconnected components, resulting in the failure of the hierarchical network organization itself. We show that finding a 2-SRLG-connected partitioning for a given network is NP-complete and provide a distributed heuristic approach. Simulation results verify that the proposed 2-SRLG-connected partitioning scheme performs better than traditional 1-connected partitioning approaches with regard to survivability and system stability.

In this paper, we study restoration mechanisms to handle channel and link failures in an optical WDM wavelength-routed wide-area backbone network based on a mesh topology. The solution uses a small number of tunable lasers per link to provide restoration capability. In addition to link failures, we consider individual channel failures link-level mechanisms are presented: redirection algorithm (RDA) and disjoint path algorithm (DPA). These mechanisms use WDM-specific link information to compute the link restoration routes. We present results based on discrete-event simulations to understand the performance of the proposed mechanisms, in terms of restoration efficiency and restoration times. The results show that for networks of varying size and node degree with 32 wavelengths on each link, using as few as 8 tunable lasers per link provides good restoration efficiency under moderate traffic load. which might occur when one or more transceivers fail at the source of the lightpath or due to a failure in the switch fabric. Restoration is first attempted using the tunable lasers to transmit on the failed wavelengths. If all the failed lightpaths cannot be restored using the tunable lasers, unused wavelengths on the same link are used (this requires optical wavelength conversion at the nodes). For the remaining lightpaths requiring restoration, link-level restoration mechanisms are attempted. Two different

P4Resilience: Scalable Resilience for Multi-failure Recovery in SDN with Programmable Data Plane

The current state of security and availability of the Internet is far from being commensurate with its importance. The number and strength of DDoS attacks conducted at the network layer have been steadily increasing. However, the single path (SP) routing used in today’s Internet lacks a mitigation scheme to rapidly recover from network attacks or link failure. In case of a link failure occurs, it can take several minutes until failover. In contrast, multi-path routing can take advantage of multiple alternative paths and rapidly switch to another working path. According to the level of available path control, we classfy the multi-path routing into two types, first-hop multi-path (FMP) and multi-hop multi-path (MMP) routing. Although FMP routing supported by networks, such as SD-WAN, shows marginal improvements over the current SP routing of the Internet, MMP routing supported by a global Internet architecture provides strong improvement under network attacks and link failure. MMP routing enables changing to alternate paths to mitigate the network problem in other hops, which cannot be controlled by FMP routing. To show this comparison with practical outcome, we evaluate network performance in terms of latency and loss rate to show that MMP routing can mitigate Internet hazards and provide high availability on global networks by 18 participating ASes in six countries. Our evaluation of global networks shows that, if network attacks or failures occur in other autonomous systems (ASes) that FMP routing cannot avoid, it is feasible to deal with such problems by switching to alternative paths by using MMP routing. When the global evaluation is under a transit-link DDoS attack, the loss rates of FMP that pass the transit-link are affected significantly by a transit-link DDoS attack, but the other alternative MMP paths show stable status under the DDoS attack with proper operation.