12069557
Blocking behaviors of crosstalk-free optical Banyan networks on vertical stacking
Banyan networks are attractive for constructing directional coupler (DC)-based optical switching networks for their small depth and self-routing capability. Crosstalk between optical signals passing through the same DC is an intrinsic drawback in DC-based optical networks. Vertical stacking of multiple copies of an optical banyan network is a novel scheme for building nonblocking (crosstalk-free) optical switching networks. The resulting network, namely vertically stacked optical banyan (VSOB) network, preserves all the properties of the banyan network, but increases the hardware cost significantly. Though much work has been done for determining the minimum number of stacked copies (planes) required for a nonblocking VSOB network, little is known on analyzing the blocking probabilities of VSOB networks that do not meet the nonblocking condition (i.e., with fewer stacked copies than required by the nonblocking condition). In this paper, we analyze the blocking probabilities of VSOB networks and develop their upper and lower bounds with respect to the number of planes in the networks. These bounds depict accurately the overall blocking behaviors of VSOB networks and agree with the conditions of strictly nonblocking and rearrangeably nonblocking VSOB networks respectively. Extensive simulation on a network simulator with both random routing and packing strategy has shown that the blocking probabilities of both strategies fall nicely within our bounds, and the blocking probability of packing strategy actually matches the lower bound. The proposed bounds are significant because they reveal the inherent relationships between blocking probability and network hardware cost in terms of the number of planes, and provide network developers a quantitative guidance to trade blocking probability for hardware cost. In particular, our bounds provide network designers an effective tool to estimate the minimum and maximum blocking probabilities of VSOB networks in which different routing strategies may be applied. An interesting conclusion drawn from our work that has practical applications is that the hardware cost of a VSOB network can be reduced dramatically if a predictable and almost negligible nonzero blocking probability is allowed.
2194314
Shared protection based on matrix decomposition in tropical semi-rings
It is observed that the singular value decomposition (SVD) transformation based on min-plus algebra (or called tropical semi-rings) leads to a very good characteristic in zero underestimating the reconstructed matrix. This paper introduces a novel distributed control framework for shared protection in optical networks with reduced routing information based on the tropical semi-rings technique, called sharing with reduced information with tropical semi-rings (SRI-TROP). The design of the proposed framework aims to initiate a compromise between the amount of link-state dissemination and the performance impairment due to the incompleteness of routing information, such that the precision in the link-state matrix reconstruction can efficiently map to the reduction in blocking probability. Based on the framework, a series of novel schemes are proposed, which are verified and compared with the reported counterparts in a simulation. The simulation results show that the performance in terms of the precision in the reconstructed link-state and the resultant blocking probability can be significantly improved.
30106346
A Genetic Algorithm for Dynamic Routing and Wavelength Assignment in WDM Networks
In this paper, we study the challenging problem of Dynamic Routing and Wavelength Assignment (DRWA) in WDM (Wavelength-Division-Multiplexing) networks with wavelength continuity constraint, and propose an improved genetic algorithm (GA) for it. By adopting a new fitness function to consider simultaneously the path length and number of free wavelengths in cost estimation of a route, the new genetic RWA algorithm can achieve a good load balance among route candidates and result in a lower blocking probability than both the fixed alternative routing algorithm and the previous GA-based algorithm for DRWA, as verified by an extensive simulation study upon the ns-2 network simulator and some typical network topologies.
42869695
Dynamic RWA Based on the Combination of Mobile Agents Technique and Genetic Algorithm in WDM Networks with Sparse Wavelength Conversion
In this paper, we study the dynamic RWA problem in WDM networks with sparse wavelength conversion and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithm. By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously update the routing tables, the new hybrid algorithm has the ability to promptly determine the first population of routes for a new request based on the routing table of its source node without requiring the time consuming process associated with the available GA-based dynamic RWA algorithms. To achieve a good load balance in WDM networks with sparse wavelength conversion, we adopt in our hybrid algorithm a new reproduction scheme and a new fitness function that simultaneously takes into account the path length, number of free wavelengths and wavelength conversion capability in route selection. Our new algorithm has the capabilities of achieving a better load balance and resulting a significantly lower blocking probability than that of the promising fixed-alternate routing algorithm for both the optical networks with sparse and full-range wavelength converters and the optical networks with sparse and limited-range wavelength converters, as verified by an extensive simulation study upon the ns-2 network simulator. The ability to guarantee both a low blocking probability and a small setup delay makes the new hybrid dynamic RWA algorithm very attractive for both the optical circuit switching networks and future optical burst switching networks.
61072281
A new scheme for lightpath restoration in wdm networks
All-optical networks with wavelength division multiplexing capability are the promising candidates for the next generation Internet. As these networks carry enormous bandwidth, it is not optional for them to be survivable. Although the available proactive restoration schemes provide 100% restoration guarantee, they require a huge extra capacity and usually result in an extremely high blocking probability. In this paper, we propose a novel active scheme that uses multiple predefined but not reserved backup paths along a working path to restore the lightpath in the event of link-failure. Simulation results based on two typical networks indicate that our new restoration method can reduce blocking probability and capacity requirement significantly while guaranteeing a very high restoration probability.
22047646
Performance of Fast Routing Algorithms in Large Optical Switches Built on the Vertical Stacking of Banyan Structures
AbstractVertical stacking of multiple optical banyan networks is a novel scheme for building banyan-based nonblocking optical switches. The resulting network, namely vertically stacked optical banyan (VSOB) network, preserves the properties of small depth and absolutely loss uniformity but loses the nice self-routing capability of banyan networks. To guarantee a high switching speed, routing in VSOB network needs special attentions so that paths can be established as fast as possible. The best known global routing algorithm for an N × N nonblocking VSOB network has the time complexity of O(Nlog N), which will introduce an unacceptable long delay in path establishment for a large size optical switch. In this paper, we propose two fast routing algorithms for the VSOB network based on the idea of inputs grouping. The two algorithms, namely plane fixed routing (PFR) algorithm and partially random routing (PRR) algorithm, have the time complexities of O(log N) and O(
$$\sqrt N $$
) respectively, and FR algorithm can actually turn a VSOB network into a self-routing one. Extensive simulation based on a network simulator indicates that for large VSOB networks our new algorithms can achieve a reasonably low blocking probability while guarantee a very high switching speed.
5799803
Protection mechanisms for application service hosting platforms
The application service hosting platform (ASHP) has recently received tremendous attention from both industry and academia. An ASHP provides a shared high-performance infrastructure to host different application services (AS), outsourced by application service providers (ASP). In this paper, we focus on the protection of ASHP which has inherent requirement of sharing, openness, and mutual isolation. In contrast to a dedicated server platform, which is analogous with a private house, an ASHP is like an apartment building, involving the 'host' - the ASHP infrastructure, and the 'tenants' - the AS. Strong protection and isolation must be provided between the host and the tenants, as well as between different tenants. Unfortunately, traditional OS architecture and mechanisms are not adequate to provide strong ASHP protection. In this paper we first make the case for a new OS architecture based on the virtual OS technology. We then present three protection mechanisms we have developed in SODA, our ASHP architecture. The mechanisms include: (1) resource isolation between AS; (2) virtual switching and firewalling between AS; and (3) kernelized intrusion detection and logging for each AS. For (3), we have developed a system called Kernort inside the virtual OS kernel. Kernort detects network intrusions in real-time and logs AS activities even when the AS has been compromised. Moreover for the privacy of AS, logs are encrypted by Kernort so that the 'landlord' (namely ASHP owner) cannot view them without authorization. We are applying SODA to iShare, an Internet-based distributed resource sharing platform.
1475648
VIOLIN: Virtual Internetworking on Overlay Infrastructure
We propose a novel application-level virtual network architecture called VIOLIN (Virtual Internetworking on OverLay INfrastructure). VIOLINs are isolated virtual networks created on top of an overlay infrastructure (e.g., PlanetLab). Entities in a VIOLIN include virtual end-hosts, routers, and switches implemented by software and hosted by physical overlay hosts. Novel features of VIOLIN include: (1) a VIOLIN is a “virtual world” with its own IP address space. All its computation and communications are strictly con.ned within the VIOLIN. (2) VIOLIN entities can be created, deleted, or migrated on-demand. (3) Value-added network services not widely deployed in the real Internet can be provided in a VIOLIN. We have designed and implemented a prototype of VIOLIN in PlanetLab.
38206015
A Scalable HLA-Based Distributed Simulation Framework for VR Application
HLA-based Distributed Simulation technology is employed widely in Virtual Reality (VR) applications, such as military simulation, internet games, roaming etc. To support larger number of participants, scalability is becoming a key issue of VR applications. In this paper, we explore the characteristics of distributed simulation, and analyze the scalability of servers and participants, and classify our approach to improve scalability of VR applications into three aspects: a three-tier node management mode to accommodate more participants, an efficient management of servers to manage scalable number of clients and software development interface to achieve reusability and interoperability of VR applications. We present our middleware platform, HIVE, providing a scalable HLA-based distributed simulation framework for VR applications, on which users can develop VR applications easily and quickly. Then we give the method and view of application integration with HIVE. Finally an experimental demo is given.
12399461
On the Minimum Common Supergraph of Two Graphs
Abstract The minimum common supergraph of two graphs, g1 and g2, is defined as the smallest graph that includes, as subgraphs, both g1 and g2. It is shown that minimum common supergraph computation can be solved by means of maximum common subgraph computation. For the latter problem, algorithms are known from the literature. It will also be shown that for a certain class of cost functions, the concept of graph edit distance is closely related with the minimum common supergraph.
724770
Learning and inferencing in user ontology for personalized semantic web services
Domain ontology has been used in many Semantic Web applications. However, few applications explore the use of ontology for personalized services. This paper proposes an ontology based user model consisting of both concepts and semantic relations to represent users' interests. Specifically, we adopt a statistical approach to learning a semantic-based user ontology model from domain ontology and a spreading activation procedure for inferencing in the user ontology model. We apply the methods of learning and exploiting user ontology to a semantic search engine for finding academic publications. Our experimental results support the efficacy of user ontology and spreading activation theory (SAT) for providing personalized semantic services.