Survivability and resilience mechanisms in modern optical fibre systems

Optical fibre networks play an increasingly prominent role in communications. As networks grow in size and complexity, the probability and impact of failures increase. In this dissertation, different optical network concepts, survivability and resilience methods are considered. Link and Path failures are discussed and Static Path Protection (SPP), Shared Backup Path Protection (SBPP), as well as Path Restoration (PR) are investigated. A Shared Backup Path Protection model and simulation tool is designed and implemented. This implementation is compared with other studies. Dual-link failures are considered under specific network topologies. Shortest Path algorithms are used to reprovision optimal routes for backup protection. Results and conclusions are discussed in detail, giving valuable insight into resilience methods. Availability and protectability are discussed and evaluated as measures of resilience and network survivability. Results vary between compromising little availability and bringing a significant improvement in availability. It is concluded that the implementation of SBPP is a necessity in highly-meshed networks with high availability needs, but doesn’t necessarily provide the best solution for sparsely-connected networks. The additional cost involved in the implementation needs to be considered carefully.Dissertation (MEng)--University of Pretoria, 2007.Electrical, Electronic and Computer Engineeringunrestricte

Exploiting Excess Capacity for Survivable Traffic Grooming in Optical Backbone Networks

Backbone networks usually have some excess capacity (EC) to accommodate traffic fluctuations and to avoid early capacity exhaustion. Network operators can exploit EC in optical wavelength division multiplexed (WDM) backbone networks to support survivable traffic grooming, where connection requests are of subwavelength granularity and each provisioned request has to be protected from single-link failures. We investigate novel EC management techniques that can improve network performance, in terms of Service-Level Agreement (SLA) violations and bandwidth blockings, with no requirement of deploying additional capacity. We investigate exploiting and managing EC by the following techniques. i) Preprovisioning: When traffic is light, network resources are reserved by a preprovisioning scheme, i. e., a connection can be provisioned on reserved protected links to increase availability. We show that preprovisioning also decreases connection setup time, an important metric for delay-sensitive services. ii) Backup reprovisioning: Since high-availability protection schemes usually consume more resources, connections in our solution can be switched to a protection scheme that provides lower availability (but higher resource efficiency) by reprovisioning backup resources when traffic increases. iii) Hold-lightpath: We propose a new "hold-lightpath" scheme to exploit EC. This scheme prevents the termination of pre-established (but unused) resources to increase availability and decrease connection setup time. We compare our techniques with traditional protection schemes for typical daily fluctuating traffic on typical backbone network topologies and find that significant improvements can be achieved in terms of decreasing SLA violations, bandwidth blocking, and connection setup time

Disaster Resilient Optical Core Networks

During the past few years, the number of catastrophic disasters has increased and its impact sometimes incapacitates the infrastructures within a region. The communication network infrastructure is one of the affected systems during these events. Thus, building a resilient network backbone is essential due to the big role of networks during disaster recovery operations. In this thesis, the research efforts in building a disaster-resilient network are reviewed and open issues related to building disaster-resilient networks are discussed. Large size disasters not necessarily impact the communication networks, but instead it can stimulate events that cause network performance degradation. In this regard, two open challenges that arise after disasters are considered one is the short-term capacity exhaustion and the second is the power outage. First, the post-disaster traffic floods phenomena is considered. The impact of the traffic floods on the optical core network performance is studied. Five mitigation approaches are proposed to serve these floods and minimise the incurred blocking. The proposed approaches explore different technologies such as excess or overprovisioned capacity exploitation, traffic filtering, protection paths rerouting, rerouting all traffic and finally using the degrees of freedom offered by differentiated services. The mitigation approaches succeeded in reducing the disaster induced traffic blocking. Second, advance reservation provisioning in an energy-efficient approach is developed. Four scenarios are considered to minimise power consumption. The scenarios exploit the flexibility provided by the sliding-window advance reservation requests. This flexibility is studied through scheduling and rescheduling scenarios. The proposed scenarios succeeded in minimising the consumed power. Third, the sliding-window flexibility is exploited for the objective of minimising network blocking during post-disaster traffic floods. The scheduling and rescheduling scenarios are extended to overcome the capacity exhaustion and improve the network blocking. The proposed schemes minimised the incurred blocking during traffic floods by exploiting sliding window. Fourth, building blackout resilient networks is proposed. The network performance during power outages is evaluated. A remedy approach is suggested for maximising network lifetime during blackouts. The approach attempts to reduce the required backup power supply while minimising network outages due to limited energy production. The results show that the mitigation approach succeeds in keeping the network alive during a blackout while minimising the required backup power

Design of Resilient Ethernet Ring Protection (ERP) Mesh Networks With Improved Service Availability

Ethernet Ring Protection (ERP) has recently emerged to provide protection switching for Ethernet ring topologies with sub-50 ms failover capabilities. ERP's promise to provide protection in mesh packet transport networks positions Ethernet as a prominent competitor to conventional SONET/SDH and as the technology of choice for carrier networks. Higher service availability, however, in ERP has been challenged by the issue of network partitioning and contention for shared capacity caused by concurrent failures. In this paper, we show that in a network designed to withstand single-link failure, the service availability, in the presence of double link failures, depends on the designed ERP scheme, i.e., the RPL placement as well as the selection of ring hierarchy. Therefore, we present a study for characterizing service outages and propose a design method which strikes a balance between capacity requirement and service availability (i.e., the number of service outages resulting from concurrent failures). We observe that through effective design, remarkable reduction in service outages is obtained at a modest increase in capacity deployment

Novel Approaches and Architecture for Survivable Optical Internet

Any unexpected disruption to WDM (Wavelength Division Multiplexing) based optical networks which carry data traffic at tera-bit per second may result in a huge loss to its end-users and the carrier itself. Thus survivability has been well-recognized as one of the most important objectives in the design of optical Internet. This thesis proposes a novel survivable routing architecture for the optical Internet. We focus on a number of key issues that are essential to achieve the desired service scenarios, including the tasks of (a) minimizing the total number of wavelengths used for establishing working and protection paths in WDM networks; (b) minimizing the number of affected working paths in case of a link failure; (c) handling large scale WDM mesh networks; and (d) supporting both Quality of Service (QoS) and best-effort based working lightpaths. To implement the above objectives, a novel path based shared protection framework namely Group Shared protection (GSP) is proposed where the traffic matrix can be divided into multiple protection groups (PGs) based on specific grouping policy, and optimization is performed on these PGs. To the best of our knowledge this is the first work done in the area of group based WDM survivable routing approaches where not only the resource sharing is conducted among the PGs to achieve the best possible capacity efficiency, but also an integrated survivable routing framework is provided by incorporating the above objectives. Simulation results show the effectiveness of the proposed schemes

Heuristic for the design of fault tolerant logical topology.

Wavelength division multiplexing (WDM) in optical fiber networks is widely viewed as the savior for its potential to satisfy the huge bandwidth requirement of network users. Optical cross connect (OCX) in WDM network facilitates the switching of signal on any wavelength from any input port to any output port. As a result, it is possible to establish ligthpaths between any pair of nodes. The set of lightpaths established over fiber links defines logical topology. In our thesis, we proposed a heuristic approach for the design of fault tolerant logical topology. Our design approach generalizes the design protection concept and enforces wavelength continuity constraint in a multi-hop optical network. In our work, we first designed logical topology for fault free state of the network. We, then, added additional lightpaths for each single link failure scenario. Numerical results clearly show that our approach outperforms Shared path protection and Dedicated path protection. Our simulation result shows that our approach is feasible for large networks. (Abstract shortened by UMI.) Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2005 .S24. Source: Masters Abstracts International, Volume: 44-03, page: 1413. Thesis (M.Sc.)--University of Windsor (Canada), 2005

Novel Approaches and Architecture for Survivable Optical Internet

Any unexpected disruption to WDM (Wavelength Division Multiplexing) based optical networks which carry data traffic at tera-bit per second may result in a huge loss to its end-users and the carrier itself. Thus survivability has been well-recognized as one of the most important objectives in the design of optical Internet. This thesis proposes a novel survivable routing architecture for the optical Internet. We focus on a number of key issues that are essential to achieve the desired service scenarios, including the tasks of (a) minimizing the total number of wavelengths used for establishing working and protection paths in WDM networks; (b) minimizing the number of affected working paths in case of a link failure; (c) handling large scale WDM mesh networks; and (d) supporting both Quality of Service (QoS) and best-effort based working lightpaths. To implement the above objectives, a novel path based shared protection framework namely Group Shared protection (GSP) is proposed where the traffic matrix can be divided into multiple protection groups (PGs) based on specific grouping policy, and optimization is performed on these PGs. To the best of our knowledge this is the first work done in the area of group based WDM survivable routing approaches where not only the resource sharing is conducted among the PGs to achieve the best possible capacity efficiency, but also an integrated survivable routing framework is provided by incorporating the above objectives. Simulation results show the effectiveness of the proposed schemes