Weigang Hou

Multi-path routing in Spatial Wireless Ad Hoc networks

In recent years, Spatial Wireless Ad Hoc (SWAH) networks constructed in the near spatial region by connecting various pieces of spatial and ground communication equipment have become the focus for developing future information networks. Due to their special characteristics, the traditional routing protocols in fixed networks and ad hoc networks cannot be used directly in SWAH networks. Therefore, the design of a special routing protocol for SWAH networks has become a challenge. In this paper, we propose a new Hybrid On-demand Distance Vector Multi-path (HODVM) routing protocol that divides the SWAH networks into backbone and non-backbone networks to perform static routing and dynamic routing, respectively. To provide load balancing, HODVM can adaptively establish and maintain multiple node-disjoint routes by multi-path routing. Simulation results show that, compared to traditional routing protocol, HODVM not only has better performance in terms of scalability and survivability but can also balance the network load well.

Robust and Integrated Grooming for Power- and Port-Cost-Efficient Design in IP Over WDM Networks

Fueled by the growing resource crisis and potential economic incentives, significant research attention has recently been devoted to improving the power efficiency of IP over Wavelength-Division-Multiplexing (WDM) networks. Previous works on power savings in IP over WDM networks have required explicit knowledge of the traffic between each network node pair and the resource assignment of each fiber link. However, it is difficult to accurately estimate this information in live networks due to the inherent features of IP traffic, e.g., bursts, unpredictability and variability. Furthermore, the number of ports consumed in Optical Cross-Connects (OXCs) trends to grow due to the use of traffic grooming and optical bypasses for power savings. Therefore, it is necessary to achieve joint power efficiency and port savings in live IP over WDM networks where the traffic between each network node pair and resource assignment of each fiber link are not known in advance. Since the problem of grooming, routing and wavelength/waveband assignment is NP-hard, a new heuristic approach, the Robust and Integrated Grooming (RIG) algorithm, is proposed in this paper. RIG uses a novel metric, a power ratio defined by the power consumed over the power saved, to evaluate the power efficiency. By determining the Traffic Distribution Vector (TDV) with the lowest power ratio using the Minimizing Power Ratio First (MPRF) method, the previously unknown information can be acquired. By performing traffic matrix transformations, we construct a green optical virtual topology to groom connection demands into established lightpaths using Hybrid Grooming Schemes (HGSs) for power efficiency and waveband switching for port savings. The simulation results demonstrate that RIG can, on average, achieve power efficiency and port savings of 15% and 32%, respectively, compared to state-of-the-art robust grooming methods. To the best of our knowledge, this paper is the first work addressing robust and integrated grooming for power- and port-cost-efficient design in IP over WDM networks.

Energy saving and cost reduction in multi-granularity green optical networks

With the energy consumption increase and the greenhouse effect becomes more and more serious, the energy saving has become the focus in the whole world. At the same time, as the network traffic largely growing, the size and the cost of network equipments keep increasing so that the network cost reduction is also very important. In recent years, the concept of green Internet was proposed to construct an energy-efficient and cost-optimal green network. In this paper, we firstly present the current studies working on the energy saving and cost reduction in multi-granularity optical network that is the convergence between IP network and optical network to support both the low-speed IP data and the high-speed optical transmission. After analyzing the current studies, in our opinion, the traffic grooming mechanism with optical bypass technology is the feasible solution by binding a lot of low-rate IP data into a few of high-speed lightpaths to reduce a lot of electrical ports consumption in IP routers for saving the energy, the waveband switching mechanism is the feasible solution by binding multiple lightpaths into a few of waveband tunnels to save the optical transmitting ports consumption in Multi-Granularity Optical Cross-Connects (MG-OXCs) for reducing the network costs, and the multi-granularity grooming mechanism is the feasible solution by integrating the traffic grooming with the waveband switching to achieve both the energy saving and cost reduction. Based on our opinion, this paper proposes the challenging issues including the network node model, virtual topology design, certain traffic matrix and uncertain traffic matrix for energy saving and cost reduction in multi-granularity optical network, with possible solutions and preliminary simulation results to guide the future work.

Local and global hamiltonian cycle protection algorithm based on abstracted virtual topology in fault-tolerant multi-domain optical networks

Since current optical network is actually divided into multiple domains each of which has its own network provider for independent management, the development of multi-domain networks has become the trend of next-generation intelligent optical networks, and then the survivability has also become an important and challenging issue in fault-tolerant multi-domain optical networks. In this paper, we study protection algorithms in multi-domain optical networks and propose a new heuristic algorithm called multi-domain Hamiltonian cycle protection (MHCP) to tolerate the single-fiber link failure. In MHCP, we present the local Hamiltonian cycle (LHC) method based on the physical topology of each single-domain and the global Hamiltonian cycle (GHC) method based on the abstracted virtual topology of multi-domains to protect the intra-fiber link and inter-fiber link failures, respectively. We also present the link-cost formulas to encourage the load balancing and proper links selection for computing the working path of each connection request. Simulation results show that, compared with previous multi-domain protection algorithm, MHCP can obtain better performances in resource utilization ratio, blocking probability, and computation complexity.

Multicast Grooming Algorithm in Waveband Switching Optical Networks

In optical Wavelength-Division-Multiplexing (WDM) networks, multicast becomes more and more popular to provide high-speed communication between one point and multiple points. At the same time, the ports of Optical Cross-Connect (OXC) are greatly enhanced with the increasing number of wavelengths in fibers, and then the waveband switching technique is proposed to save the ports and reduce the cost of OXC. However, current waveband grooming algorithms are all limited in unicast. To achieve the multicast communication and meanwhile save the ports of OXC, we need to solve the multicast grooming, routing and wavelength/waveband assignment problem which is the HP-hard. In this paper, we propose a heuristic algorithm named Integrated Multicast Waveband Grooming (IMWG) based on Multicast Layered Auxiliary Graph (MLAG) that includes a Virtual Topology Layer (VTL) and multiple Waveband-Plane Layers (WPLs) to support the single-hop, multi-hop and hybrid multicast waveband grooming. For each demand, IMWG first computes a single-hop or multi-hop grooming waveband-tree on VTL. If the grooming waveband-tree cannot be found on VTL, IMWG computes a new waveband-tree on WPL. If the new waveband-tree cannot be found on WPL, IMWG computes a hybrid grooming waveband-tree on MLAG. Simulation results show that, compared with other algorithms, IMWG is able to obtain better performances.

A new heuristic protection algorithm based on survivable integrated auxiliary graph in waveband switching optical networks

In this paper, we study the survivability in waveband switching optical networks and propose a new heuristic algorithm called Protection based on Survivable Integrated Auxiliary Graph (PSIAG) to tolerate the single-link failure. The survivable integrated auxiliary graph (SIAG) is compared of the single virtual topology layer and multiple waveband-plane layers, and it can well solve the problem of routing and waveband assignment. In PSIAG, we can feasible use the waveband sub-path grouping scheme based on SIAG to save the switching ports in MG-OXCs. For each demand, PSIAG first computes the single-hop or multi-hop route-pair including a primary path and a link-disjoint backup path on virtual topology layer. If the route-pair cannot be found on virtual topology layer, PSIAG then computes the hybrid multi-hop route-pair on jointing the virtual topology layer and waveband-plane layers. Simulation results show that PSIAG can obtain better performance than previous algorithm.

Virtual network planning for converged optical and data centers: ideas and challenges

With the development of WDM techniques and cloud computing, incorporating the optical backbone into data centers has received extensive attention. Virtual network (VN) planning has been proposed for this new networking paradigm by taking advantage of network virtualization. VN planning is essentially a united virtualization of optical and server resources in a collaborative manner. In this article, we first elaborate the advantages and problems of existing VN planning schemes through a comprehensive survey. Next, we provide a VN planning scheme. The simulation results demonstrate the effectiveness of our strategy, particularly in the context of power outage and evolving recovery. Finally, the future opportunities and challenges are also discussed.

Multi-granularity and robust grooming in power- and port-cost-efficient IP over WDM networks

Previous studies on the power efficiency or port savings in IP over WDM networks have required explicit knowledge of the traffic between each network node pair and the resource assignment of each fiber link. However, it is difficult to estimate this information accurately in live networks, due to the inherent features of IP traffic, e.g., bursts, unpredictability, and variability. Furthermore, the granularity of the demands on an IP-level connection tends to be diverse, and the number of ports consumed in Optical Cross-Connects (OXCs) tends to grow due to the use of hybrid grooming (i.e., traffic grooming with an optical bypass) for power savings. Therefore, it is critical to achieve both power efficiency and port savings in realistic IP over WDM networks. In this paper, we investigate the problem of multi-granularity and robust grooming for power- and port-cost-efficient IP over WDM networks. First, a key parameter, the Multi-Granularity Power Ratio (MGPR), which is the sum of the different single-granularity power ratios, is proposed. Second, the MMPR (Minimizing Multi-granularity Power Ratio) method is used to compute the Traffic Distribution Vectors. Finally, we present the multi-granularity and robust grooming approach, called the Maximizing Hop First (MXHF) approach, where hybrid grooming is adopted to improve power efficiency and waveband merging is utilized to reduce the port cost. Simulation results demonstrate that the MXHF approach can achieve power efficiency and port savings comparing with state-of-the-art robust grooming methods.

Multicast multi-granular grooming based on integrated auxiliary grooming graph in optical networks

In order to improve the bandwidth utilization efficiency and reduce the blocking probability for multicast requests in optical networks, the multicast traffic grooming approach was proposed to groom a lot of low-speed traffic to a few of high-speed light-trees. At the same time, in order to save the ports and the cost of optical cross-connect, the multicast waveband grooming approach was proposed to groom multiple light-trees to a few of waveband tunnels. However, the existing approaches all did not consider the joint performances of improving bandwidth utilization efficiency, reducing blocking probability and saving ports for multicast requests. Therefore, in this article, we propose a new multicast multi-granular grooming approach to perform the hierarchical sequential grooming to improve the joint performances based on a newly developed integrated auxiliary grooming graph (IAGG) that includes multiple wavelength integrated grooming graphs (WIGGs) and one waveband virtual topology layered graph (BVLG) to support both the multicast traffic grooming and multicast waveband grooming. In order to achieve the map of light-tree to the virtual topology layer in WIGG or BVLG, we present a light-segment map method, where a light-tree will be divided to several light-segments each of which will be independently mapped to the virtual topology layer. Since different definitions of blocking probability may lead to different objectives, we define two kinds of blocking probability, mean blocking probability of requests (MBPR) and mean blocking probability of users (MBPU). According to the two definitions of blocking probability, we propose two multicast multi-granular grooming heuristic algorithms, Heuristic Algorithm with minimizing MBPR and Heuristic Algorithm with minimizing MBPU based on IAGG. Simulation results show that the two proposed algorithms are both efficient and have better performances than traditional multicast grooming algorithm.

Joint port-cost and power-consumption savings in hybrid hierarchical optical networks

In optical networks, with the number of wavelengths in fibers increasing, the size and cost of Optical Cross-Connects (OXC) have been increased. Waveband merging technology, which groups several wavelength routes into a single waveband tunnel with at least two hops, could perform port-cost savings by reducing the size and cost of OXC since switching one waveband in the All Optical (OOO) domain only consumes two ports at each bypass node. On the other hand, the absence of wavelength conversion restricts the capability of OOO-OXC. Therefore, designing a hybrid hierarchical node to transmit wavebands in an OOO switch and add/drop local requests or perform wavelength conversion in an Optical-Electrical-Optical (OEO) switch has been one of the promising solutions for next-generation optical networks. However, due to the increasing effects of greenhouse gases and the drastic consumption of power, port-cost and power-consumption savings are becoming the new and twin objectives to further develop hybrid hierarchical optical networks. In this paper, we jointly consider port-cost and power-consumption in a hybrid hierarchical optical network and propose efficient approaches including Integer Linear Programming (ILP) models and heuristics. Simulation results of two heuristic approaches, a Cost and Power savings algorithm based on an End-to-End waveband Merging strategy (CPEEM) as well as a Cost and Power savings algorithm based on a Sub-Path waveband Merging strategy (CPSPM), show that the cost of Transmitting Ports (TPs) used in an OOO switch is in contrast to the use of the power consumed by the OEO part of a hybrid hierarchical node. Moreover, comparing with CPEEM, CPSPM has a better performance for port-cost savings but the performance improvement is at the cost of higher power consumption in an OEO switch. On the contrary, CPEEM has a better performance for power-consumption savings but the performance improvement is achieved at the expense of a higher cost of transmitting ports comparing with CPSPM. Based on the parameter, Boundary of Consumed Power (BCP), a New Integrated Algorithm (NIA) that could effectively choose between CPEEM or CPSPM according to the current network state is proposed to obtain the trade-off performances.