Connection availability analysis of span-restorable mesh networks

Dual-span failures are the key factor of the system unavailability in a mesh-restorable network with full restorability of single-span failures. Availability analysis based on reliability block diagrams is not suitable to describe failures of mesh-restorable networks with widely distributed and interdependent spare capacities. Therefore, a new concept of restoration-aware connection availability is proposed to facilitate the analysis. Specific models of span-oriented schemes are built and analyzed. By using the proposed computation method and presuming dual-span failures to be the only failure mode, we can exactly calculate the average connection unavailability with an arbitrary allocation rule for spare capacity and no knowledge of any restoration details, or the unavailability of a specific connection with known restoration details. Network performance with respect to connection unavailability, traffic loss, spare capacity consumption, and dual failure restorability is investigated in a case study for an optical span-restorable long-haul networ

Survivable mesh-network design & optimization to support multiple QoP service classes

Every second, vast amounts of data are transferred over communication systems around the world, and as a result, the demands on optical infrastructures are extending beyond the traditional, ring-based architecture. The range of content and services available from the Internet is increasing, and network operations are constantly under pressure to expand their optical networks in order to keep pace with the ever increasing demand for higher speed and more reliable links

Risk based resilient network design

This paper presents a risk-based approach to resilient network design. The basic design problem considered is that given a working network and a fixed budget, how best to allocate the budget for deploying a survivability technique in different parts of the network based on managing the risk. The term risk measures two related quantities: the likelihood of failure or attack, and the amount of damage caused by the failure or attack. Various designs with different risk-based design objectives are considered, for example, minimizing the expected damage, minimizing the maximum damage, and minimizing a measure of the variability of damage that could occur in the network. A design methodology for the proposed risk-based survivable network design approach is presented within an optimization model framework. Numerical results and analysis illustrating the different risk based designs and the tradeoffs among the schemes are presented. © 2011 Springer Science+Business Media, LLC

Availability-Aware Spare Capacity Allocation with Partially Protected Rings

This thesis work focuses on designing a survivable IP-core network with the minimal investment of spare capacity. A span-oriented spare capacity allocation (SCA) scheme is proposed to satisfy customers' availability requirements in the end-to-end (E2E) sense. The novelty of the proposed SCA scheme is that it meets the E2E availability requirements despite the lack of knowledge of E2E bandwidth by employing protection rings covering all links in the network. Different ring selection methods are presented and also compared from the aspect of network redundancy and LP feasibility which provide more flexibility to the design. The proposed SCA algorithm further minimizes total cost of spare capacity by incorporating partial protection within the proposed architecture. The simulation results show that it can significantly reduce the spare capacity consumption depending on the availability. The proposed SCA scheme also performs better in terms of redundancy than that of two other dominant methods available these days

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

Optimization Methods for Optical Long-Haul and Access Networks

Optical communications based on fiber optics and the associated technologies have seen remarkable progress over the past two decades. Widespread deployment of optical fiber has been witnessed in backbone and metro networks as well as access segments connecting to customer premises and homes. Designing and developing a reliable, robust and efficient end-to-end optical communication system have thus emerged as topics of utmost importance both to researchers and network operators. To fulfill these requirements, various problems have surfaced and received attention, such as network planning, capacity placement, traffic grooming, traffic scheduling, and bandwidth allocation. The optimal network design aims at addressing (one or more of) these problems based on some optimization objectives. In this thesis, we consider two of the most important problems in optical networks; namely the survivability in optical long-haul networks and the problem of bandwidth allocation and scheduling in optical access networks. For the former, we present efficient and accurate models for availability-aware design and service provisioning in p-cycle based survivable networks. We also derive optimization models for survivable network design based on p-trail, a more general protection structure, and compare its performance with p-cycles. Indeed, major cost savings can be obtained when the optical access and long-haul subnetworks become closer to each other by means of consolidation of access and metro networks. As this distance between long-haul and access networks reduces, and the need and expectations from passive optical access networks (PONs) soar, it becomes crucial to efficiently manage bandwidth in the access while providing the desired level of service availability in the long-haul backbone. We therefore address in this thesis the problem of bandwidth management and scheduling in passive optical networks; we design efficient joint and non-joint scheduling and bandwidth allocation methods for multichannel PON as well as next generation 10Gbps Ethernet PON (10G-EPON) while addressing the problem of coexistence between 10G-EPONs and multichannel PONs

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