The article first presents a broad overview of the fault management mechanisms involved in deploying a survivable optical mesh network which employs optical crossconnects. We review various protection and restoration schemes, primary and back-up route computation methods, shareability optimization, and dynamic restoration. We then describe different parameters that can measure the quality of service provided by a WDM mesh network to upper protocol layers (e.g., IP network backbones, ATM network backbones, leased lines, virtual private networks), such as service availability, service reliability, restoration time, and service restorability. We review these concepts, the factors that affect them, and how to improve them. In particular, we present a framework for cost-effective availability-aware connection provisioning to provide differentiated services in WDM mesh networks. Through the framework, the more realistic scenario of multiple near-simultaneous failures can be handled. In addition, the emerging problem of protecting low-speed connections of different bandwidth granularities is also reviewed.

A review of fault management in WDM mesh networks: basic concepts and research challenges

Telecommunications networks, and in particular optical WDM networks, are vulnerable to large-scale failures in their physical infrastructure, resulting from physical attacks (such as an electromagnetic pulse attack) or natural disasters (such as solar flares, earthquakes, and floods). Such events happen at specific geographical locations and disrupt specific parts of the network, but their effects cannot be determined exactly in advance. Therefore, we provide a unified framework to model network vulnerability when the event has a probabilistic nature, defined by an arbitrary probability density function. Our framework captures scenarios with a number of simultaneous attacks, when network components consist of several dependent subcomponents, and in which either a 1 + 1 or a 1:1 protection plan is in place. We use computational geometric tools to provide efficient algorithms to identify vulnerable points within the network under various metrics. Then, we obtain numerical results for specific backbone networks, demonstrating the applicability of our algorithms to real-world scenarios. Our novel approach allows to identify locations that require additional protection efforts (e.g., equipment shielding). Overall, the paper demonstrates that using computational geometric techniques can significantly contribute to our understanding of network resilience.

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The resilience of WDM networks to probabilistic geographical failures

Survivability against disasters-both natural and deliberate attacks, and spanning large geographical areas-is becoming a major challenge in communication networks. Cloud services delivered by datacenter networks yield new opportunities to provide protection against disasters. Cloud services require a network substrate with high capacity, low latency, high availability, and low cost, which can be delivered by optical networks. In such networks, path protection against network failures is generally ensured by providing a backup path to the same destination (i.e., a datacenter), which is link-disjoint to the primary path. This protection fails to protect against disasters covering an area which disrupts both primary and backup paths. Also, protection against destination (datacenter) node failure is not ensured by a generic protection scheme. Moreover, content/service protection is a fundamental problem in a datacenter network, as the failure of a datacenter should not cause the disappearance of a specific content/service from the network. So content placement, routing, and protection of paths and content should be addressed together. In this work, we propose an integrated Integer Linear Program (ILP) to design an optical datacenter network, which solves the above-mentioned problems simultaneously. We show that our disaster protection scheme exploiting anycasting provides more protection, but uses less capacity than dedicated single-link failure protection. We show that a reasonable number of datacenters and selective content replicas with intelligent network design can provide survivability to disasters while supporting user demands. We also propose ILP relaxations and heuristics to solve the problem for large networks.

Design of Disaster-Resilient Optical Datacenter Networks

We investigate the survivable traffic-grooming problem for optical mesh networks employing wavelength-division multiplexing (WDM). In the dynamic provisioning context, a typical connection request may require bandwidth less than that of a wavelength channel, and it may also require protection from network failures, typically fiber cuts. Based on a generic grooming-node architecture, we propose three approaches for grooming a connection request with shared protection: protection-at-lightpath level (PAL); mixed protection-at-connection level (MPAC); separate protection-at-connection level (SPAC). In shared-mesh protection, backup paths can share resources as long as their corresponding working paths are unlikely to fail simultaneously. These three schemes explore different ways of backup sharing, and they trade-off between wavelengths and grooming ports. Since the existing version of the problem for provisioning one connection request with shared protection is NP-complete, we propose effective heuristics. Under today's typical connection-bandwidth distribution where lower bandwidth connections outnumber higher bandwidth connections, we find the following: 1) it is beneficial to groom working paths and backup paths separately, as in PAL and SPAC; 2) separately protecting each individual connection, i.e., SPAC, yields the best performance when the number of grooming ports is sufficient; 3) protecting each specific lightpath, i.e., PAL, achieves the best performance when the number of grooming ports is moderate or small.

Traffic grooming for survivable WDM networks - shared protection

The transport network paradigm is moving toward next-generation networks that aim at IP convergence, while architectures and technologies are diversifying. Video technologies including ultrahigh-definition TV (more than 33 M pixels) continue to advance, and future communication networks will become video-centric. The inefficiencies of current IP technologies, in particular, the energy consumption and throughput limitations of IP routers, will become pressing problems. Harnessing the full power of light will resolve these problems and spur the creation of future video-centric networks. Extension of optical layer technologies and coordination with new transport protocols will be critical; hierarchical optical path technologies and optical circuit/path switching will play key roles. Recent technical advances in these fields are presented.

Optical Networking Technologies That Will Create Future Bandwidth-Abundant Networks [Invited]

Shared-Path Protection for Resource Efficiency.- Sub-Path Protection for Scalability and Fast Recovery.- Segment Protection for Bandwidth Efficiency and Differentiated Quality of Protection.- Survivable Traffic Grooming-Dedicated Protection.- Survivable Traffic Grooming-Shared Protection.- Survivable Virtual Concatenation for Data Over Sonet/Sdh.

Survivable Optical WDM Networks

We investigate the survivable traffic-grooming problem for optical mesh networks employing wavelength-division multiplexing (WDM) and dedicated protection. We consider the dynamic-provisioning environment in which a connection arrives at random, holds for a random amount of time, and then departs. A typical connection request may require bandwidth less than that of a wavelength, and it may also require protection from network failures, typically fiber cuts. On the basis of generic grooming-node architecture, we propose two approaches--protection-at-lightpath (PAL) level and protection-at-connection (PAC) level--for grooming a connection request. Here we investigate dedicated protection. In a companion paper [IEEE J. Sel. Areas Commun. 21, 1367 (2003)], we investigate shared protection, which leads to a substantially different treatment. For dedicated protection, we prove that the problem of provisioning a connection under PAC is NP-complete, propose effective heuristics for both schemes, and define comprehensive performance metrics to compare PAL with PAC with respect to wavelength or grooming-port efficiency. Our findings are as follows. Under today's typical connection-bandwidth distribution in which lower-bandwidth connections outnumber higher-bandwidth connections, PAC outperforms PAL (in terms of bandwidth-blocking ratio, lightpath use, and wavelength use) if the number of grooming ports is large; however, PAL outperforms PAC (in terms of bandwidth-blocking ratio and grooming-port use) when the number of grooming ports is moderate or small.

Traffic grooming for survivable WDM networks: dedicated protection [Invited]

Traffic grooming deals with efficiently packing/unpacking low-speed connections onto high-capacity trunks. We examine traffic grooming for optical mesh networks by reviewing grooming-node architectures, traffic models, grooming policies, novel graph models, survivable grooming, and hierarchical switching, etc.

Traffic grooming in mesh optical networks

As networks migrate from stacked rings to meshes because of the poor scalability of interconnected rings and the excessive resource redundancy used in ring-based protection [MacDonald et al., 2000], mesh-structured protection schemes have been receiving increasing attention [Doshi et al., 1999, Ramamurthy et al., 2003, Iraschko et al., 1998, Van Caenegem et al., 1998, Crochat et al., 2000, Miyao and Saito, 1998, Mohan et al., 2001]. We review the work on WDM mesh protection for a given set of lightpath requests (which is the focus of this chapter), and classify them based on whether they treat the underlying mesh as a whole, or they fragment the mesh into other protection domains [Gerstel and Ramaswami, 2000a], or they split an end-to-end lightpath into different segments.

Sub-Path Protection for Scalability and Fast Recovery

We investigate the problem of provisioning shared-mesh-protected sub-wavelength connections in wavelength-convertible optical WDM networks. We propose protection-at-lightpath (PAL) level and protection-at-connection (PAC) level. We found PAL outperforms PAC in such network settings.

Canhui Sam Ou

Papers

Survivable Optical WDM Networks

Traffic grooming for survivable WDM networks: dedicated protection [Invited]

Traffic grooming in mesh optical networks

Sub-Path Protection for Scalability and Fast Recovery

Survivable traffic grooming in WDM mesh networks