Manav Mishra

An Interval-Based Scheduling Algorithm for Optical WDM Star Networks

This paper considers scheduling algorithms for multiple access protocols associated with wavelength division multiplexed (WDM) multi-channel optical networks based on the star topology. To share the available channels among nodes, several demand assignment multiple access protocols based on reservation schemes have been proposed. The core of such reservation-based protocols is the scheduling algorithm, which allocates channels and time slots to the nodes based on traffic demand. The key objectives of the scheduling algorithm design are maximization of network utilization and minimization of packet delay. There is a trade-off between these two requirements: it takes more computation time to achieve a better utilization, which in turn will increase packet delay. This trade-off directly affects the overall network performance. Another important requirement is the consideration of transceiver tuning latencies. In this paper, we propose an on-line scheduling algorithm called OIS (On-line Interval-based Scheduling) to balance these requirements and increase network throughput. We also require that the scheduling algorithms be simple so that hardware implementation is feasible to reduce overall delay. We compare our scheduling algorithm to the Transmission Assignment Algorithm (TAA) studied by Borella and Mukherjee (1996); and to a matrix decomposition algorithm studied by Sivalingam and Wang (1996). We show that our algorithm, although suffering from small utilization loss, requires significantly less computation time and results in higher network throughput. In particular, for higher network speeds such as 2.4 Gbps per channel, the potential improvement using our algorithm is substantial. We also provide conditions when either protocol performs better compared to the other.

A Hybrid Protection-Restoration Mechanism for Enhancing Dual-Failure Restorability in Optical Mesh-Restorable Networks

In this paper, we investigate the problem of enhancing dual-failure restorability in path-protected mesh-restorable optical wavelength division multiplexed (WDM) networks. A key finding of recent studies that have demonstrated the need to survive simultaneous dual-link failures is that designs providing complete (i.e. 100%) protection from all dual-failures may need almost thrice the spare capacity compared to a system that protects against all single-link failures. However, it has also been shown that systems designed for 100% single-link failure protection can provide reasonable protection from dual-link failures. Thus, the motivation of this work is to develop a hybrid mechanism that provides maximum (close to 100%) dual-failure restorability with minimum additional spare capacity. The system architecture considered is a circuit-switched WDM network with dynamic arrival of sessions requests. We also consider sparse wavelength conversion, where only some nodes have converters. We propose an adaptive mechanism, which we term active protection, that builds upon a pro-active path protection to provide complete single-failure restorability and adds dynamic segment-based restoration. The objective is to optimize network survivability (and minimize spare capacity needs) with ragard to dual-link failures while maintaining complete single-failure restorability. The basic premise of the algorithm is to identify scenarios in the dual-link failure model that necessitate additional spare capacity and provide protection for those scenarios only. Our findings indicate that the proposed scheme achieves close to complete (100%) dual-failure restorability with only maximum of 3% wavelength-links needing two backups even at high loads. Moreover, at moderate to high loads, our scheme attains close to 16% improvement over the base model that provides complete single-failure restorability.

Scheduling in optical WDM networks using hidden Markov chain-based traffic predictors

This paper presents the design and performance analysis of a predictor-based scheduling algorithm for optical wavelength division multiplexed (WDM) networks. A reservation-based multiple access control (MAC) protocol which schedules reservation requests from the network nodes on the multiple channels. We reduce the amount of time spent in computing the schedule by predicting traffic requests. The performance analysis based on discrete-event simulation, varying the parameters such as number of nodes and channels is presented.

Restoration mechanisms based on tunable lasers for handling channel and link failures in optical WDM networks

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

Restoration mechanisms for handling channel and link failures in optical WDM networks: tunable laser-based switch architectures and performance analysis

In this paper, we study restoration mechanisms to handle channel and link failures in an optical wavelength division multiplexed (WDM) wavelength-routed wide-area backbone network based on a mesh topology. The solution uses a small number of tunable lasers to provide restoration capability. We consider two types of failures: link failures and individual channel (or wavelength) failures that occur when one or more transceivers fail at a node that is the source of lightpath(s) or due to a failure in an intermediate nodes optical switch fabric. We use the restoration mechanism that attempts to find alternate paths and resources after failure occurs. In our proposed mechanism, 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, if optical wavelength conversion is available. For the remaining lightpaths requiring restoration, two different link-level restoration mechanisms called redirection algorithm (RDA) and disjoint path algorithm (DPA) are used. Results based on discrete-event simulations to understand the performance of the proposed mechanisms, in terms of restoration efficiency and restoration times, are presented. The results show that for networks of varying size and node degree with 32 wavelengths on each link, using as few as eight tunable lasers per link provides good restoration efficiency under moderate traffic load. The performance of the proposed algorithms is compared to an earlier restoration mechanism based on broadcast, and it is seen that the proposed mechanism performs better, by offering both lower restoration times and higher restoration efficiency even with a small number of lasers. The impact of the number of tunable lasers on the performance is studied for failures occurring simultaneously on two links. It is seen that for a small number of such channel failures, as few as four tunable lasers per link are sufficient to recover from failures on a single link and on two links.

Enabling Architectures for Next Generation Optical Networks

As the demand grows for higher network access speeds, technologies such as optical fiber have begun to overtake traditional copper wire for data transport in short haul networks as well as long haul networks. Optical networking plays a growing role in next generation networks with new capabilities such as LCAS (Link Capacity Adjustment Scheme) and Virtual Concatenation (VC), and services such as dynamic provisioning and traffic grooming. While these emerging capabilities hold the promise of an intelligent optical network, there are still obstacles. Protocols and standards to support these capabilities are still evolving. In addition, in order to realize the new benefits, carriers and providers must invest in new optical equipment, as well as upgrades to existing equipment. In the current economic environment, a choice which leverages lower cost equipment with software which can provide advanced functionality is significantly more attractive than expensive alternatives. In addition, upgradeable software-based components provide future cost savings as well as flexibility in supporting new and changing protocols and standards. In this paper, we discuss each of these issues in detail and present a solution for optical services and applications, including Optical Burst Switching, using a network processor based platform to overcome the obstacles facing next generation optical networks.