Virtual Topology Research Articles

An Autonomic Virtual Topology Design and Two-Stage Scheduling Algorithm for Light-Trail WDM Networks

Light-trails (LTs) have been proposed as a solution for optical networking to provide support for emerging services such as video-on-demand, pseudo-wires, data-centers, etc. To provision these services we require features such as dynamic bandwidth provisioning, optical multicasting, sub-wavelength grooming and a low-cost hardware platform-all of which are available through the LT concept. Architectural, performance, resilience and implementation studies of LTs have led to consideration of this technology in metropolitan networks. In the area of architecture and performance, significant literature is available in terms of static network optimization. An area that has not yet been considered and which is of service provider importance (from an implementation perspective) is the stochastic behavior and dynamic growth of the LT virtual topology. In this paper, we propose a two-stage scheduling algorithm that efficiently allocates bandwidth to nodes within a LT and also grows the virtual topology of LTs based on basic utility theory. The algorithm facilitates growth of the LT topology fathoming across all the necessary and sufficient parameters. The algorithm is formally stated, analyzed using Markov models and verified through simulations, resulting in 45% betterment over existing linear program (LP) or heuristic models. The outcome of the growth algorithm is an autonomic optical network that suffices for service provider needs while lowering operational and capital costs. This paper presents the first work in the area of dual topology planning-at the level of connections as well as at the level of the network itself.

Dynamic routing at different layers in IP-over-WDM networks — Maximizing energy savings

We estimate potential energy savings in IP-over-WDM networks achieved by switching off router line cards in low-demand hours. We compare three approaches to react on dynamics in the IP traffic over time, Fufl, Dufl and Dudl. They provide different levels of freedom in adjusting the routing of lightpaths in the WDM layer and the routing of demands in the IP layer. Using MILP models based on three realistic network topologies as well as realistic demands, power, and cost values, we show that already a simple monitoring of the lightpath utilization in order to deactivate empty line cards ( Fufl) may bring substantial benefits. The most significant savings, however, are achieved by rerouting traffic in the IP layer ( Dufl). A sophisticated reoptimization of the virtual topology and the routing in the optical and electrical domains for every demand scenario ( Dudl) yields nearly no additional profits in the considered networks. These results are independent of the ratio between the traffic demands and capacity granularity, the time scale, distribution of demands, and the network topology for Dufl and Dudl. The success of Fufl, however, depends on the spatial distribution of the traffic as well as on the ratio of traffic demands and lightpath capacity.

Overview and Challenges of Overlay Networks: A Survey

Nowadays, a very useful platform is becoming widely used to deploy new services and applications in the Internet: the overlay networks. These networks create a virtual topology on top of existing ones with the purpose of providing several different services such as file sharing or content delivery. This survey focuses on diverse research issues concerning overlay networks applicability and management strategies required for emergent network environments. In this way, mobility, security, scalability, dependability and resource constraints are studied with regard to overlay networks. We finally discuss the evolution of these networks in order to satisfy new technological improvements.

Personal Network Construction System Using Mobile Phones

Despite the recent advances in personal communication devices and access network technology, users still face problems such as high device maintenance costs, complication of inter-device cooperation, illegal access to devices, and leakage of personal information. Consequently, it is difficult for users to construct a secure network with local as well as remote personal devices. We propose a User-driven Service Creation Platform (USCP), which enables users to construct a secure private network using a simple and intuitive approach that leverages the authentication mechanism in mobile phone networks. USCP separates signaling and data paths in a flat, virtual network topology. In this paper, we describe the basic design of USCP, the current implementation, and system evaluations.

Virtual Topology Design for Minimizing Network Diameter and Average Hop Count in WDM Networks

We design virtual topologies in wavelength division multiplexing (WDM) networks to minimize the network diameter and average hop count, where network diameter refers to the number of hops of the longest shortest path and average hop count is the average number of hops among the shortest paths of all node pairs. Such objectives are important to WDM networks, especially to those with statistical multiplexing mechanisms such as optical burst switching (OBS) and optical packet switching (OPS). By minimizing the network diameter and average hop count, optical packets or bursts will experience less contention loss and smaller delay due to a reduced number of intermediate nodes en route. In this paper, we first formulate an integer linear program (ILP) for optimal design of virtual topologies with minimized network diameter and average hop count. Then, a novel heuristic least weight minimum diameter (LWMD) is proposed to find good solutions efficiently. Based on the virtual topology obtained, we further design two traffic accommodation schemes to provision wavelengths under a given traffic matrix, with guaranteed network diameter and minimized network resource consumption.

Dynamic waveband grooming based on hierarchical integrated grooming auxiliary graph in multi-domain mesh optical networks

With the number of wavelengths in fibers increasing, the number of optical switching ports in conventional Optical Cross-Connect (OXC) keeps enhancing, so that waveband grooming technique is proposed to save the switching ports in OXC. Most of previous works focused on waveband grooming in single-domain optical network. Since the current optical backbone is actually divided to multiple domains according to the different network providers, it is necessary to study the waveband grooming in multi-domain optical networks. However, waveband grooming in multi-domain optical networks is more challenging than that in single domain networks because of the routing scalability and security issues. Therefore, in this paper, we propose a new heuristic Hierarchical Multi-domain Waveband Grooming (HMWG) algorithm based on Hierarchical Integrated Grooming Auxiliary Graph (H-IGAG) to reduce the total number of optical switching ports. The H-IGAG is compared of the Intra-domain Waveband Integrated Auxiliary Graph (Intra-WIAG) and the Inter-domain waveband Virtual Topology Graph (Inter-VTG). For the demand in single-domain, HMWG directly computes the route from the source node to destination node in the single-domain with waveband grooming on Intra-WIAG. For the demand spanning different domains, HMWG first computes the route from the source node to the selected border node in source domain and computes the route from the selected border node to the destination node in destination domain with waveband grooming on Intra-WIAG, respectively. Then, HMWG computes the route from the selected border node in source domain to the selected border node in destination domain with waveband grooming on Inter-VTG. Simulation results show that, compared with previous grooming algorithm, HMWG can obtain better performance.

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.

Integrated routing in GMPLS-based IP/WDM networks

The Internet traffic evolution has forced network operators to migrate toward an integrated infrastructure which brings the IP and optical layers under a unified model. The integration between the two technologies has been facilitated by the development of the Generalized Multi Protocol Label Switching. In the integrated scenario, Multilayer Traffic Engineering can be reinforced with integrated routing techniques. Integrated IP/WDM routing facilitates the routing decision phase by allowing a node to have a complete knowledge of the IP and WDM domains when accommodating traffic. This study focuses on integrated IP/WDM routing. We analyze two basic policies widely discussed in literature: one policy prioritizes the traffic accommodation on the virtual topology, while the other prioritizes the traffic accommodation on the physical topology. We show that both the mechanisms do not lead to efficient resource utilization because they tend to congest one layer more than the other one. We propose an adaptive heuristic which combines the advantages of both the policies. When accommodating traffic, the proposed approach selects the appropriate layer depending on the resource utilization being experienced in the virtual and the physical topologies. We demonstrate via simulations that the cross-layer resource optimization executed by the proposed scheme achieves significant improvements in terms of blocking ratio.

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.

Distributed dynamic grooming routing and wavelength assignment in WDM optical mesh networks

The bandwidth of a wavelength channel in WDM optical networks is very high compared to the user's requirements for various applications. Therefore, there is a scope for better utilization of channel bandwidth by traffic grooming, in which several user's channels are multiplexed for transmission over a single channel. Several research works have been reported on traffic grooming routing and wavelength assignment (GRWA) for static and dynamic traffic pattern under centralized environment. Distributed dynamic grooming routing and wavelength assignment (DDGRWA) is a new and quite unexplored area in WDM optical mesh networks. This article introduces the concept of distributed traffic grooming in WDM mesh networks which also includes virtual topology construction, reconfiguration, routing and wavelength assignment in the distributed environment assuming incoming traffic to be dynamic in nature. We have also presented simulation results of our algorithm on dynamically generated traffic under various network topologies.

Ensuring Resilience in Optical WDM Networks With Nature-Inspired Heuristics

One of the most important issues in optical network design is ensuring its resilience. In this paper, we propose using nature-inspired heuristics to find a resilient mapping of a given virtual topology with minimum resource usage. Evolutionary algorithms and ant colony optimization algorithms are applied to the problem after a set of parameter tuning tests. To assess the performance of the proposed algorithms, we compare the experimental results with those obtained through integer linear programming. The results show that both of our algorithms can solve the problem even for large-scale network topologies for which a feasible solution cannot be found using integer linear programming. Moreover, the CPU time and the memory used by the nature-inspired heuristics is much lower. The solution quality and the CPU time usage results prove that both of our nature-inspired heuristics can easily be applied to real-world applications.

On Symmetry for Network Virtual Topology

General networks such as Internet are complex heterogeneous networks, which are constructed by many different organizations, and so become non-effective ones. Therefore one constructed a level of software over networks which is called overlay or virtual topology. In this paper we present principle of symmetry for general network topology by using Cayley graph models and show its necessity to improving network performance. We explain the main conclusions of the paper by many examples in optical, wireless and peer-to-peer networks.

Hybrid Algorithms for Routing and Assignment Wavelengths in Optical Networks

This paper presents a strategy for the solution of the WDM optical networks planning. Specifically, the problem of Routing and Wavelength Allocation (RWA) in order to minimize the amount of wavelengths used. In this case, the problem is known as the Min-RWA. Two meta-heuristics (Tabu Search and Simulated Annealing) are applied to take solutions of good quality and high performance. The key point is the degradation of the maximum load on the virtual links in favor of minimization of number of wavelengths used; the objective is to find a good compromise between the metrics of virtual topology (load in Gb/s) and of the physical topology (quantity of wavelengths). The simulations suggest good results when compared to some existing in the literature.

Survivable routing algorithm with mixed shared protection in fault‐tolerant GMPLS multi‐layered optical networks

AbstractIn this paper, we studied survivability in general multi‐protocol label switching (GMPLS) multi‐layered optical networks and proposed a novel mixed shared protection algorithm (MSPA) based on the integrated layered graph (ILG) to tolerate single‐fibre link failure. The ILG is composed of one virtual topology layer (VTL), corresponding to IP/MPLS layer; multiple wavelength‐plane layers (WPLs), corresponding to the wavelength‐division multiplexing (WDM) optical layer; and some virtual links that connect the VTL to each WPL in order to solve the problem on routing, wavelength assignment and low‐speed traffic grooming. For every connection request, the MSPA first computes a single‐hop or multi‐hop label switching path (LSP) pair, involving a working LSP and a physical link‐disjoint backup LSP in the VTL. If the LSP pair is not found in the VTL, the MSPA computes the new LSP pair in the WPL. Conversely, if the new LSP pair is not detected in the WPL, the MSPA computes the hybrid multi‐hop LSP pair in the ILG. In the MSPA, if the two working LSPs are in physical link‐disjoint, their corresponding backup LSPs can share the backup bandwidth. In addition, the working LSPs and the backup LSPs can also share the same mixed of wavelength, in which the different bandwidths can be assigned to different working and backup LSPs. Simulation results show that, compared to previous algorithm, the MSPA can obtain a better bandwidth utilisation ratio (BUR) with a lower blocking probability. Copyright © 2010 John Wiley & Sons, Ltd.

A GRASP-based network re-optimization strategy for improving RWA in multi-constrained optical transport infrastructures

In wavelength-routed optical networks, end-to-end connection demands are dynamically routed according to the current network status. Naïve path selection schemes, the wavelength continuity constraint and the limited or inaccurate information available can cause the virtual topology resulting from the currently allocated lightpaths to become sub-optimal. We propose an efficient re-optimization technique based on a GRASP meta-heuristic. Our work is focused on a hybrid online–offline scenario: connections are ordinarily routed dynamically using one of the available algorithms for online routing, but occasionally, when reorganization of the current virtual topology is desirable, existing paths are re-routed in order to improve load balancing and hence the ability to efficiently accept further connections. Because global changes of the logical topology and/or routing scheme can be disruptive for the provided connection services, we used iterative stepwise approaches based on a sequence of small actions (i.e., single connection re-routing and on local search from a given configuration). Simulation results demonstrate that several network performance metrics – including connection blocking ratios and bandwidth gains – are significantly improved by such approach. In particular, we achieved to accept more connection requests in our re-optimized networks with respect to the same networks without re-optimization, thus lowering the blocking ratio. Besides, in all tests we measured a notable gain in the number of freed bandwidth OC-units thanks to our re-optimization approach.

Fairness in Zone-Based Algorithms for Dynamic Traffic Grooming in WDM Mesh Networks

Dynamic grooming deals with requests for wavelength allocation based on a dynamic pattern of arrivals in contrast to the situation of static grooming in which the pattern of arrivals must be previously known. Solutions for dynamic grooming typically involve the construction of an auxiliary graph for deciding on the routing and wavelength assignment. An auxiliary graph can represent the network partially leading to scalable solutions; however, a previous proposal employing a reduced auxiliary graph produces blocking that is not fairly distributed among calls. A novel algorithm is thus proposed in this paper for achieving fairness in relation to the blocking of calls. This algorithm uses alternative routing rather than shortest-path routing as well as auxiliary graphs based on the virtual topology. Results reveal a higher degree of fairness obtained by the use of the novel algorithm than by previously proposed algorithms.

Modeling and Analysis of Source Management Routing Scheme for BGP

S ource management routing scheme called SMR is a new approach that provides a backup routing path for BGP on AS-level. In SMR, each AS in the virtual ring just is defined by a node which owns a unique identifier. It is a novel way to integrate some physical topology into virtual topology to shorten the routes greatly. And then, we present a theoretical model of virtual ring SMR to describe the routing mechanism and the impact s on the routing performance. We evaluate the performance of SMR by simulations on a real BGP topology. In the case of each AS only maintaining a route to one virtual neighbor, virtual ring SMR still provides a path to destination with low overhead. Furthermore, our theoretical model fit the process of SMR well, and provides the insight for us to improve the virtual ring SMR.

Special issue on virtualization

Virtualization has always been an enabler for efficient management in networking environments. The recent developments in hardware and software virtualization that emerged in the last few years now open new and very promising perspectives to more flexible networks, paving the way for new advanced services. However, to enable these evolutions to become one of the core building blocks of the future Internet, many challenges still need to be addressed. In this special issue of the International Journal of Network Management, three papers present different approaches to virtualization and its utilization for improving networks and their management. The paper entited ‘Using Virtual Topologies to Manage Inter-domain QoS in Next Generation Networks’ by Madeira et al. proposes the virtualization of network topologies to ease inter-domain quality of service management. The paper entitled ‘Specifying and provisioning Virtual Infrastructures with HIPerNET’, by Anhalt et al., extends the model of virtualization to both computing resources and networks so as to enable full infrastructure virtualization. Finally, the paper entitled ‘Characterizing User-level Network Virtualization: Performance, Overheads and Limits’, by Tsugawa et al., provides a study on the performance of virtualized networks built as overlays among standard operating systems nodes. This special issue on ‘Network Virtualization and Its Management’ received ten submissions from around the world, out of which the three papers mentioned above have been selected. Every submitted paper has been reviewed by four experts from a committee composed of nine researchers in the field.

Protection schemes with waveband grooming in fault-tolerant multidomain optical networks

In wavelength-division-multiplexing networks, the fault-tolerance is very important since failures may lead to a significant amount of data loss. At the same time, the waveband switching technique is very interesting since it can save switching ports in optical cross-connections. In addition, the hierarchical routing in multidomain optical networks is very challenging since the interdomain routing is based on aggregative virtual topology. However, previous works did not jointly consider the three issues. We propose two schemes, segment-based protection (SBP) and path-based protection (PBP), to provide the fault-tolerance and waveband grooming in multidomain optical networks. In SBP, for each connection we first compute an interdomain loose route based on virtual topology, and then we compute the intradomain exact path-pairs in each single domain traversed by the loose route based on physical topology. In PBP, for each connection we first compute an interdomain loose primary path and an interdomain loose backup path based on virtual topology, and then we compute the intradomain exact paths in each single domain traversed by the loose primary path and backup path based on the physical topology. To support multidomain waveband grooming, we present the layered auxiliary graph. Simulation results show that PBP performs better than SBP.

Waveband Grooming based on Layered Auxiliary Graph in multi-domain optical networks

With the number of wavelengths on fibers keeps increasing, the size and the cost of Optical Cross-Connect (OXC) are greatly enhanced and then the control and management of optical switches become more and more complicated. Therefore, the technique called waveband switching is proposed to reduce the size and the cost of OXC; that is, to save the All-Optical (OOO) switching ports in OXC. However, the existing waveband switching algorithms are all limited in single-domain optical networks. Actually, with the scale of optical backbone keeps enlarging, the network is divided to multiple independent domains to perform the hierarchy routing for achieving the scalability. In order to reduce the size and the cost of OXC meanwhile to achieve the scalability in multi-domains, in this paper we propose a new heuristic algorithm called Waveband Grooming with Layered Auxiliary Graph (WGLAG) since the waveband grooming problem is the NP-hard to perform the inter-domain routing based on the virtual topology of multi-domain network and the intra-domain routing based on the physical topology of single-domain network. In intra-domain routing with waveband grooming of each single-domain, we propose the Layered Auxiliary Graph (LAG) that includes one virtual topology layer and multiple waveband-plane layers to compute a single-hop, or multi-hop or hybrid waveband route for each connection request based on the sub-path waveband grooming scheme. Simulation results show that, WGLAG not only can effectively save more switching ports to reduce the cost of OXC but also can obtain lower blocking probability than other algorithm.