Sun Il Kim

Capacity-efficient protection with fast recovery in optically transparent mesh networks

Survivability becomes increasingly critical in managing high-speed networks as data traffic continues to grow in both size and importance. In addition, the impact of failures is exacerbated by the higher data rates available in optical networks. It is therefore imperative to address network survivability in an efficient manner in order to design and operate reliable networks. Transparent optical networks (TONs) provide several advantages over optically opaque networks for supporting the growing communication demands, but suffer from several drawbacks that reduce the efficacy of most applicable capacity-efficient survivability techniques. In this paper, we introduce a novel protection algorithm (for single link and node failures) called streams. The streams algorithm is similar to 1:1 dedicated path protection in terms of implementation and operation overhead, and has identical recovery speeds while requiring less capacity. We compare the streams algorithm with dedicated and shared path protection in terms of capacity requirements, path lengths, and recovery time. We also extend the flooding based mesh restoration algorithm (FBMR) in order to provide a fair comparison in online routing scenarios, and report the relative tradeoffs between the different algorithms. Our results show that dynamically routed streams offer attractive tradeoffs in terms of capacity, path length, recovery speed, data loss and implementation complexity.

Restoration of all-optical mesh networks with path-based flooding

The exponential growth of data traffic has led to substantial deployment of wavelength-division multiplexing networks. Reliability becomes increasingly important as the number of critical applications that depend on proper operation of these networks grows. Protection against failures of links or nodes can be achieved using a wide variety of approaches, which offer tradeoffs in terms of speed of recovery, cost of equipment, protection capacity, and management overhead. Optically transparent networks provide several advantages over optically opaque networks for supporting the growing communication demands, but suffer from several drawbacks that make direct application of the most capacity-efficient protection schemes difficult. In this paper, we introduce a flooding-based recovery scheme for optically transparent networks that provides 100% recovery from all single link and node failures in a capacity-efficient manner. In essence, this scheme applies the notion of active flooding of backup traffic introduced by generalized loopback to the problem of path protection. Our recovery scheme can achieve fast restoration (comparable to rings) with little data loss by using backup traffic flooding without the overhead of signaling and setup of intermediate cross-connects along the recovery path. We present simulation results for online provisioning of lightpaths with uniformly distributed traffic demands over optically transparent networks using our restoration scheme. The results show that the scheme offers an interesting tradeoff between capacity cost and recovery speed for all-optical networks. For five representative networks, the approach limits data loss to about 20 ms while using 14% less capacity relative to dedicated (1:1) mesh protection. Shared mesh protection (path protection) with a wavelength continuity constraint uses 19% less capacity with roughly 90 ms of data loss.

Dimensioning WDM Networks for Dynamic Routing of Evolving Traffic

New Internet applications are increasingly generating high-bandwidth and short-lived demands. If network resources are available, establishing a lightpath on demand only takes a few minutes on todays reconfigurable optical networks. These demands thus create a more variable and unpredictable environment for long-term network planning. At the same time, upgrading backbone networks remains expensive and infrequent. Dimensioning network resources to sustain variable traffic demands for a long time, while requiring fewer upgrades to achieve high performance, has become a challenging problem. Two kinds of dimensioning problems for optical opaque networks are proposed and studied in this paper: basic dimensioning allocates network resources for a newly built network, and incremental dimensioning allocates extra resources for future demand growth and variations. We propose new metrics to quantify the traffic load and the traffic pattern evolution for dynamically routed networks. We evaluate the performance under load scaling, traffic evolution, and misdimensioning. We show that a dimensioned network can sustain a much higher load while providing the same performance compared with misdimensioned ones. Our approach is better adapted to traffic evolution than a uniform allocation and an asymptotic optimization approach proposed earlier.

Minimizing Protection Cost for High-Speed Recovery of Mission Critical Traffic in WDM Mesh Networks

Network survivability depends on the choice of recovery scheme and offers challenging tradeoffs in terms of recovery speed, cost, and management complexity. To allow more efficient operation of backbone networks, service differentiation based on reliability requirements have been proposed. However, the cost for protecting mission critical data using high-speed recovery schemes can still be expensive. We previously described an online protection scheme called Streams Protection that allows fast recovery and low data loss with little extra capacity. In this paper, we present a capacity optimization technique using the Streams Protection scheme for use with static traffic demands consisting of high-priority traffic. Unlike the use of flexible, dynamic provisioning, which is desirable for non-critical traffic (may be blocked depending on resource availability), high-priority, mission critical traffic must be guaranteed a high level of reliability and stability, which lends itself better to more static provisioning models. Our results show that using the proposed technique, we can achieve significant savings in protection capacity while providing the recovery speed and low data loss figures of a fully dedicated protection scheme.

Robust dimensioning and routing for dynamic WDM networks

Advances in device technology and dense wavelength division multiplexing have enabled modern optical backbones to provide high data rate services in a cost-effective manner. At the same time, applications are emerging with the potential to leverage these capabilities for short time spans: load migration for Internet clouds, integrated computational grids, and remote surgery. Until such applications mature, investment in real networks to support them is unattractive, but without such investment, the applications mature slowly. Current networks thus remain dominated by lightpaths provisioned by hand, over the space of days or weeks.

Towards a Deeper Understanding of Managing Dynamic Optical Networks Under Link Failures

We quantify the impact of link failures after initial rerouting and show that some nodes continue to drop a significant portion of its traffic. We discuss the practical tradeoffs in rebalancing the network using redimensioning.

Opportunity cost analysis for dynamic wavelength routed mesh networks

Optical backbone networks are becoming increasingly intelligent and flexible. These networks are able to establish high-bandwidth wavelength connections on-demand to support future network-centric applications. Choosing an efficient path in a timely manner, while considering important criteria such as operation costs and network performance, is a key problem confronting the network operators. Subtle path preferences of different dynamic routing algorithms (which are usually ignored by traditional analysis techniques) can make a significant difference in performance on mesh networks. It opens new research to advance routing algorithms in both analysis and implementation paradigms. In this paper, we propose an opportunity cost model that provides fast and accurate analysis for threshold-based online congestion-aware routing algorithms. The model is simple to compute, robust to different network topologies, and scalable. We show that our model further aids in the design of a number of new routing algorithms that can be easily applied to practical networks. In contrast to previous work, the optimal threshold values for our algorithms can be identified analytically, and the values sustain good performance on different network topologies and sizes.

Coordinated Resource Scheduling in High-performance Optical Grids

This paper investigates coordinated resource scheduling algorithms for high- performance optical grids. We introduce a simple scheduling algorithm and study its impact on grid performance.

Minimizing Vulnerability with End-to-End Protection Schemes for Optical Networks

In this paper, we present techniques that allow network end-to-end protection reconfiguration algorithms to achieve maximum robustness under multiple failures. With the presented approach, maximum robustness can be achieved for a given topology.

Understanding failure localization in mesh networks

We introduced a model for node failures and presented measures that effectively address node protection and failure localization. Results of our investigation show advantages of generalized loopback over ring-based algorithms in robustness and spare capacity in addressing node recovery and multiple failures compared to double cycle cover.