Hong-Hsu Yen

A novel delay-aware routing algorithm (DARA) for a hybrid wireless-optical broadband access network (WOBAN)

A hybrid wireless-optical broadband access network (WOBAN) is a promising architecture for future access networks. Recently, the WOBAN has been gaining increasing attention, and early versions are being deployed as municipal access solutions. This architecture saves on network deployment cost because fiber need not penetrate to each end user. However, a major research opportunity exists in developing an efficient routing algorithm for the wireless front-end of the WOBAN. We propose and investigate the characteristics of the delay-aware routing algorithm (DARA) that minimizes the average packet delay in the wireless front-end of a WOBAN. In DARA we model wireless routers as queues and predict wireless link states periodically. Our performance studies show that DARA achieves less delay and congestion, and improved load balancing compared to traditional approaches such as the minimum-hop routing algorithm, shortest-path routing algorithm, and predictive throughput routing algorithm.

Hybrid wireless-optical broadband access network (WOBAN): network planning and setup

In a WOBAN, the back end is a wired optical network, the front end is managed by wireless connectivity, and, in between, the tail ends of the optical part [known as optical network unit (ONU)] communicate directly with wireless access points (AP). We study a WOBAN deployment scenario and investigate an algorithm to optimize the placement of multiple ONUs. To obtain some representative data on locations of typical wireless users, we have conducted a survey on the distribution and types of wireless routers in the Wildhorse residential neighborhood of North Davis, CA. We also formulate the multiple-ONU deployment problem using a combinatorial optimizer, viz., simulated annealing. Having found the suitable locations for ONUs, we compare the expenditures of a WOBAN vs. a wired access solution, namely Passive Optical Network (PON). To capture the challenges behind a complete WOBAN setup, we propose and investigate a joint optimization algorithm, which considers design aspects of both the wireless front end, such as avoiding interference among neighboring APs, and the optical back end, such as minimizing expensive fiber layout.

Hybrid wireless-optical broadband access network (WOBAN): network planning using Lagrangean relaxation

The concept of a hybrid wireless-optical broadband access network (WOBAN) is a very attractive one. This is because it may be costly in several situations to run fiber to every home (or equivalent end-user premises) from the telecom central office (CO); also, providing wireless access from the CO to every end user may not be possible because of limited spectrum. Thus, running fiber as far as possible from the CO toward the end user and then having wireless access technologies take over may be an excellent compromise. How far should fiber penetrate before wireless takes over is an interesting engineering design and optimization problem, which we address in this paper. We propose and investigate the characteristics of an analytical model for network planning, namely optimum placements of base stations (BSs) and optical network units (ONUs) in a WOBAN (called the primal model, or PM). We develop several constraints to be satisfied: BS and ONU installation constraints, user assignment constraints, channel assignment constraints, capacity constraints, and signal-quality and interference constraints. To solve this PM with reasonable accuracy, we use ldquoLagrangean relaxationrdquo to obtain the corresponding ldquoLagrangean dualrdquo model. We solve this dual problem to obtain a lower bound (LB) of the primal problem. We also develop an algorithm (called the primal algorithm) to solve the PM to obtain an upper bound (UB). Via simulation, we compare this PM to a placement heuristic (called the cellular heuristic) and verify that the placement problem is quite sensitive to a set of chosen metrics.

Integrated Provisioning of Sliding Scheduled Services Over WDM Optical Networks [Invited]

Many future Internet applications supported over optical networks may require large amounts of guaranteed bandwidth between two remote end hosts, but this bandwidth may not necessarily be needed immediately. To ensure a deterministic service, Internet customers may prefer to reserve network resources, e.g., lightpaths, in advance and may indicate an approximate time window in the future during which the bandwidth should be reserved for a certain period of time; however, the exact start time of the reservation is not specified, but can slide in the predefined time window. This type of user traffic is called ldquosliding scheduled traffic.rdquo Optical network design for provisioning sliding scheduled traffic is a highly complex task that has been dealt with in the literature by two-step approaches, which first schedule user demands in time and then perform their routing and wavelength assignment (RWA). We propose a scalable integrated design for the sliding scheduling provisioning problem (SSPP), based on the Lagrangean relaxation (LR) approach, which can jointly perform the scheduling and RWA of the demands. We first develop a new mathematical model for SSPP, to which it is suitable to apply the relaxation of some of the modelpsilas constraints. We use an integrated heuristic called IPSR (integrated provisioning of sliding requests), which is next enhanced with a cost assignment based on Lagrangean multiplier information, to serve as the primal algorithm for our LR approach (named IPSR-LR). We compare our approaches with an existing two-step heuristic algorithm for SSPP and show that both IPSR and IPSR-LR are able to outperform it. In addition, our numerical results show that IPSR-LR improves over IPSR under all typical experimental cases that we considered. Furthermore, we compare our approaches with the solutions provided by an integer linear program for the SSPP, which is, however, less scalable for large problem sizes compared with our algorithms.

A Survey on Sensor Coverage and Visual Data Capturing/Processing/Transmission in Wireless Visual Sensor Networks

Wireless Visual Sensor Networks (WVSNs) where camera-equipped sensor nodes can capture, process and transmit image/video information have become an important new research area. As compared to the traditional wireless sensor networks (WSNs) that can only transmit scalar information (e.g., temperature), the visual data in WVSNs enable much wider applications, such as visual security surveillance and visual wildlife monitoring. However, as compared to the scalar data in WSNs, visual data is much bigger and more complicated so intelligent schemes are required to capture/process/transmit visual data in limited resources (hardware capability and bandwidth) WVSNs. WVSNs introduce new multi-disciplinary research opportunities of topics that include visual sensor hardware, image and multimedia capture and processing, wireless communication and networking. In this paper, we survey existing research efforts on the visual sensor hardware, visual sensor coverage/deployment, and visual data capture/processing/transmission issues in WVSNs. We conclude that WVSN research is still in an early age and there are still many open issues that have not been fully addressed. More new novel multi-disciplinary, cross-layered, distributed and collaborative solutions should be devised to tackle these challenging issues in WVSNs.

Near-optimal tree-based access network design

Among various access network topologies, the tree topology is the most popular due to its simplicity and relatively low cost. A salient example is the CATV network. In this paper, we consider the tree-based access network design problem where the operational cost and the fixed installation cost are jointly minimized. The problem is formulated as a combinatorial optimization problem, where the difficulty of solving a Steiner tree problem typically encountered in a tree-based topological design problem is particularly circumvented. The basic approach to the algorithm development is Lagrangean relaxation and the subgradient method. In the computational experiments, the proposed algorithm calculates near-optimal solutions within 3.2% of an optimal solution in 1min of CPU time for test networks of up to 26 nodes.

Traffic Grooming and Delay Constrained Multicast Routing in IP over WDM Networks

In this paper, we investigate delay constrained multicast routing for supporting QoS guaranteed point to multi-point communications in IP over WDM networks. To achieve high bandwidth utilization, packets coming from different multicast connections are groomed and carried together over a single wavelength. Lightpath scheme is adopted in this paper that unicast lightpath is provisioned to support the multicast traffic in the IP network. Hop count constraint is introduced to deal with and queueing delay from traffic grooming. The challenge of the problem comes not only from considering delay constrained multicast routing but also WDM lightpath routing and wavelength assignment (RWA). We formulated the problem as an integer optimization problem in which the revenue from admitting multicast groups is to be maximized. The problem constraints include hop count constraint for end-to-end QoS requirements, tree constraint for multicast routing, IP link capacity and WDM fiber link capacity constraints, and wavelength continuity constraint. We apply Lagrangean relaxation technique to perform constraint relaxation and propose optimization-based heuristics (LGR) to tackle this problem. We draw performance comparisons between the LGR and the minimum hop (MH) heuristics. Numerical results demonstrate that LGR outperforms MH algorithm under all experimental cases.

Traffic Grooming for IP Multicast over WDM Networks Using Light-Path and Light-Tree Schemes

In this paper, we consider one light-path based and two light-tree based traffic grooming schemes for supporting IP multicast services. We made performance comparisons for call blocking probability and bandwidth blocking probability on those schemes. Simulation results reveal that light-path scheme has lower blocking probability and less consumes bandwidth consumption as IP demand volumes are small (i.e., several Megabit/sec). On the other hand, Light-tree based schemes have better performance as the IP demands become high. We conclude that the selection of grooming strategies should take the volume of demands of the provided services into account and the results in this work can provide a basic guideline for grooming strategy selection.

QoS aware traffic grooming and integrated routing on IP over WDM networks

In this article, we consider traffic grooming and integrated routing in IP over WDM networks. The challenges of this problem come from jointly considering traffic grooming, IP routing, and lightpath routing and wavelength assignment (RWA). Due to the high bandwidth of optical fiber, there exists a mismatch between the capacity needed by an IP flow and that provided by a single lightpath. Traffic grooming is therefore used to increase the network utilization by aggregating multiple IP flows in a single lightpath. However, traffic grooming incurs additional delays that might violate Quality-of-Service (QoS) requirements of IP users. In this work, the tradeoff between traffic grooming and IP QoS routing is well-formulated as a mixed integer and linear optimization problem, in which the revenue from successfully provisioning IP paths is to be maximized. Problem constraints include IP QoS, routing, optical RWA, and the WDM network capacity. We propose a novel Lagrangean relaxation (LGR) algorithm to perform constraint relaxation and derive a set of subproblems. The Lagrangean multipliers are used in the proposed algorithm to obtain a solution in consideration of grooming advantage and resource constraints simultaneously. Through numerical experiments and comparisons between the proposed algorithm and a two-phase approach, LGR outperforms the two-phase approach under all experimental cases. In particular, the improvement ratio becomes even more significant when the ratio of IP flow to the wavelength capacity is smaller.

Near Optimal Design of Lightpath Routing and Wavelength Assignment in Purely Optical WDM Networks

This paper proposes the optimal design of lightpath Routing and Wavelength Assignment (RWA) problem in Wavelength Division Multiplexing (WDM) networks without wavelength conversion. We formulate RWA as a mixed Integer Linear Programming (ILP) problem where the objective is to minimize the cost of wavelength assignment to the fiber links in the network. The Lagrangean relaxation technique and the optimization-based heuristics are used to solve this problem. Two sets of computational experiments are performed to test the algorithms for the maximum carried traffic and minimum wavelength requirements in three different network topologies (GTE, ARPA, OCT network). Based on solution quality to the computational experiments, the error gaps between the upper bound and the lower bound are close enough that the near optimal solutions could be obtained. On the other hand, we also show that the solution quality degrade gracefully under more and more heavy traffic network environment. By assessing solution quality and the computational time, we propose the efficient and effective optimization-based algorithms based on the Lagrangean relaxation method for the RWA problem in the WDM networks without wavelength conversion.