Yurong Huang

Connection provisioning with transmission impairment consideration in optical WDM networks with high-speed channels

We investigate new connection-provisioning algorithms to efficiently provide signal-quality-guaranteed connections in an optical wavelength-division-multiplexing (WDM) mesh network operating with high-speed wavelength channels. In an optical network, a connection is set up to carry a data signal via an all-optical channel (lightpath) from its source to destination node. The optical signal transmitted along the lightpath may need to travel through a number of crossconnect switches (OXCs), optical amplifiers, and fiber segments. While the signal propagates toward its destination, the optical components would continuously degrade the signal quality by inducing impairments. When the signal degradation is so severe that the received bit-error rate (BER) becomes unacceptably high, the lightpath would not be able to provide good service quality to a connection request. Such a lightpath, which has poor signal quality due to transmission impairments in the physical layer, should not be used for connection provisioning in the network layer. With increasing channel bit rate to 10 Gb/s or higher, fiber linear and nonlinear impairments become prominent factors, which affect the signal quality. Thus, new techniques in both physical layer and network layer are necessary for mitigating impairments to accommodate high-speed traffic. Therefore, to ensure service quality of high-speed connections, we develop intelligent impairment-aware routing and wavelength assignment (RWA) algorithms, which automatically consider the effects of high-speed transmission impairment when setting up a lightpath. The main contribution of our paper is that we investigate a novel hierarchical RWA model for high-speed connection provisioning where the optical signal-to-noise ratio (OSNR) and polarization mode dispersion (PMD) effect are estimated in the physical layer, and regarded as metrics for lightpath computation in the network layer. The performance of the proposed connection-provisioning strategies is demonstrated to be promising through illustrative numerical examples.

Explicit Routing for Traffic Engineering in Labeled Optical Burst-Switched WDM Networks

Optical burst switching (OBS) is a promising technique for supporting high-capacity bursty data traffic over optical wavelength-division-multiplexed (WDM) networks. A label-switched path can be established to forward a burst control packet (BCP) if each OBS node is augmented with an IP/MPLS controller. Such a network is called a labeled OBS (LOBS) network, and it can exploit the explicit routing and constraint-based routing properties supported in the MPLS framework to perform traffic and resource engineering. In this paper, we consider the traffic-engineering problem in a LOBS network, using explicit routing to balance network load and to reduce the burst-loss probability. We model the traffic-engineering problem in a LOBS network as an optimization problem and propose two new objective functions to minimize network congestion. Our illustrative numerical examples show that the burst-loss probability can be significantly reduced using optimization technique, when compared with shortest-path routing.

Dynamic routing with preplanned congestion avoidance for survivable optical burst-switched (OBS) networks

We develop dynamic routing mechanisms for preplanned congestion avoidance in OBS networks. Based on our routing mechanisms, we propose a new protection approach against failures which significantly improves network throughput and survivability.

Studies on a Class of AWG-Based Node Architectures for Optical Burst-Switched Networks

We investigate a class of novel node architectures based on the static arrayed-waveguide gratings (AWGs) and tunable waveband converters (TWBCs) for optical burst-switched (OBS) networks. As compared to the other AWG-based architectures using tunable wavelength converters (TWCs) for switching, our design needs much fewer wavelength-converting devices, TWBCs, instead of a large number of TWCs (operating only on one wavelength at a time). Notwithstanding the inherent simplicity, AWG-based architectures, due to the static routing properties of AWGs, exhibit some internal blocking as compared to the strictly nonblocking OBS nodes employing SOA/TWC-based architectures. We address this issue in our design methodology to arrive at different candidate node architectures using multiple layers of AWGs. Our simulation results indicate that the proposed class of node architectures using TWBCs and multiple layers of AWG can offer acceptable blocking performance with a simple and cost-effective optical hardware for OBS networks.

A new fault-management method using congestion-avoidance routing for optical burst-switched networks

Optical burst switching (OBS) has been proposed as a promising technique to support high-bandwidth, bursty data traffic in the next-generation optical Internet. This study investigates a new fault-management framework for an OBS network. In an OBS network, burst-loss performance is a critical concern. In OBS, the data-burst transmission is delayed by an offset time (relative to its burst control packet (BCP), or header), and the burst follows its header without waiting for an acknowledgment for resource reservation. Thus, a burst may be lost at an intermediate node due to contention, which is generally resolved according to the local routing and bandwidth information. The routing table maintained in each OBS node is generally pre-computed and fixed to forward the data bursts. Such a static forwarding feature might have limited efficiency to resolve contentions. Moreover, a burst may be lost and the network may be congested when a network element (e.g., fiber link) fails. Therefore, for reliable burst transport, we develop dynamic routing approaches for preplanned congestion avoidance. Our goal is to proactively avoid congestion during the route-computation process, and our approach employs wavelength-channel utilization, traffic distribution, and link-distance information in the proposed objective functions for routing. Two update mechanisms for maintaining a dynamic routing table are presented to accommodate bursty data traffic. Based on our routing mechanisms, we also propose a new congestion-avoidance-and-protection (CAP) approach, which employs a primary route and a group of backup routes for each node pair against failures and congestion. The performance of the proposed protection strategy using congestion-avoidance routing is demonstrated to be promising through illustrative numerical examples.

A novel OBS node architecture using waveband-selective switching for reduced component cost and improved performance

We investigate novel waveband-selective switching for node architecture in an optical burst-switching (OBS) network. Because wavelengths are aggregated as wavebands, this architecture requires fewer components, costs less, and performs as well as traditional node designs.

A New Protection Model to Provide Availability-Guaranteed Service for Reliable Optical WDM Networks

Reliability is a crucial concern in high-speed optical networks. A service-level agreement (SLA), which mandates high service availability even in face of network failures, must be met in provisioning reliable connection. In this study, we investigate a generalized connection-provisioning and protection model to provide availability-guaranteed services in a wavelength-division multiplexing (WDM) optical mesh network. A novel link-state model is proposed to represent physical-layer availability and resource status for an optical link. This information can be used by a standard link-state routing protocol to efficiently provide reliable connections. In our proposed link-state-modeling mechanism, current network resource information and the physical components’ failure characteristics are aggregated to form a comprehensive dynamic link-state parameter, called link and resource availability (LRA). Based on such a dynamic link-state parameter, we also propose an algorithm for availability-guaranteed connection provisioning. A new generalized protection model is developed through our dynamic LRA-based provisioning. The dynamic LRA-based connection-provisioning algorithm efficiently provides SLA-guaranteed services while significantly improving connection reliability, better utilizing network resources, and achieving fast failure recovery.