Optical-LSP Establishment and a QoS Maintenance Scheme Based on Differentiated Optical QoS Classes in OVPNs

A virtual private network (VPN) over Internet has the benefit of being cost-effective and flexible. However, it has difficulties providing sufficient QoS and adequate transmission capacity for high bandwidth services. Given the increasing demand for high bandwidth Internet and the demand for QoS assurances in a VPN over Internet, IP/generalized multi-protocol label switching (GMPLS) based on a control plane combined with a high-bandwidth, dense-wavelength division multiplexing (DWDM) optical network is seen as a very favorable approach for realizing the future optical VPN (OVPN) over IP/GMPLS over DWDM. Within this architecture, providing QoS guaranteed multimedia services with a differentiated QoS guaranteed protocol framework with QoS recovery is one of the key issues to implement. Therefore, we suggest in this paper optical-label switched path (O-LSP) establishment and its QoS maintenance scheme based on differentiated optical QoS-service (DOQoS) classes. They are the key components for this DOQoS framework in assuring end-to-end QoS in an OVPN over IP/GMPLS over DWDM architecture.     

Modeling and Interoperability Test Case Generation of a Real-Time QoS Monitoring Protocol

QoS monitoring is a kind of real-time systems which allows each level of the system to track the ongoing QoS levels achieved by the lower network layers. For these systems, real-time communication between corresponding transport protocol objects is essential for their correct behavior. When two or more entities are employed to perform a certain task as in the case of communication protocols, the capability to do so is called interoperability and considered as the essential aspect of correctness of communication systems. This paper describes a formal approach on modeling and interoperability test case generation of a real-time QoS monitoring protocol. For this, we specify the behavior of flow monitoring of transport layer QoS protocol, i.e., METS protocol, which is proposed to address QoS from an end-to-end's point of view, based on QoS architecture model which includes ATM network in lower layers. We use a real-time Input/Output Finite State Machine to model the behavior of real-time flow monitoring over time. From the modeled real-time I/OFSM, we generate interoperability test cases to check the correctness of METS protocol's flow monitoring behaviors for two end systems. A new approach to efficient interoperability testing is described and the method of interoperability test cases generation is shown with the example of METS protocol's flow monitoring. The current TTCN is not appropriate for testing real-time and multimedia systems. Because test events in TTCN are for message-based system and not for stream-based systems, the real-time in TTCN can only be approximated. This paper also proposes the notation of real-time Abstract Test Suite by means of real-time extension of TTCN. This approach gives the advantages that only a few syntactical changes are necessary, and TTCN and real-time TTCN are compatible. This formal approach on interoperability testing can be applied to the real-time protocols related to IMT-2000, B-ISDN and real-time systems.     

Virtual source-based minimum interference path multicast routing in optical virtual private networks

Virtual Private Network (VPN) services over the Internet are gaining increased acceptance due to the economic benefits and flexibility. However, with difficulties of providing sufficient transmission capacity for value-added and mission-critical services, the Optical VPN (OVPN) deploying Dense Wavelength-Division Multiplexing (DWDM) technology has been seen as a favorable approach for realizing the future VPN services. In an OVPN, the Routing and Wavelength Assignment problem plays a key role for capacity utilization and therefore the Multicast Routing and Wavelength Assignment problem has been the dominant issue in a DWDM-based OVPN. In this paper, using Virtual Source (VS) nodes that have splitting and wavelength conversion capabilities, we propose a new Multicast Routing and Wavelength Assignment method for multicast sessions. The algorithm combines the VS-based tree generation approach with Multi-Wavelength Minimum Interference Path Routing (MW-MIPR) that chooses a path that does not interfere too much with potential future multicast session requests.     

Priority-based minimum interference path multicast: routing algorithm in optical virtual private network

While the “Virtual Private Network (VPN) over Internet” is cost-effective and flexible, it suffers from the difficulty of providing adequate transmission capacity for high bandwidth services. Hence a Dense Wavelength Division Multiplexing (DWDM) based “Optical VPN (OVPN)” technology has been regarded as a good alternative for realizing the future VPN services. To improve the transparency and data rate of OVPN, it is critical to consider the problem of Routing and Wavelength Assignment (RWA) for transmission capacity utilization. This paper proposes a Priority-based Minimum Interference Path Multicast Routing (PMIPMR) algorithm, a new routing algorithm which finds alternative routes based on node priorities and Virtual Source (VS) nodes that has both splitting and wavelength conversion, and then chooses a path that does not interfere with potential future multicast session requests when congestions occur in the network. The PMIPMR algorithm reduces blocking rate significantly and increases the wavelength utilization by avoiding congestion in future multicast session requests. We measured the performance of the proposed algorithm in terms of blocking rate and the resource utilization. The simulation results demonstrate that the PMIPMR algorithm is superior to the previous multicast routing algorithms using the Capability-based-Connection algorithm based on Capability-based-Priority and Spawn-from-VS methods.     

New Charge Carrier Transport-Assisting Paths in Ultra-Long GaN Microwire UV Photodetector

GaN-based materials are the hottest research topic in UV photodetectors (PDs) because of their low operating voltage, small volume, long lifetime, high-temperature resistance, and low energy consumption. However, there are still fundamental issues to be overcome, and the most important issue is to get a photoconductive gain. In this paper, the following new approaches are provided to innovatively improve the photoconductive gain of UV PDs in GaN-based materials. First, the aspect ratio of the 1D GaN microwire (MW) structure is dramatically improved by analyzing the pulse growth mechanism using the metal-organic vapor deposition system. Second, the comprehensive strain behavior in the MW epitaxial growth system is successfully analyzed. Third, the fabricated metal-semiconductor-metal-based MW UV PD shows photoresponsivity and sensitivity of 28.365 A W⁻¹ and 93.16%, respectively, at the −2 V bias, which significantly outperforms the conventional structures in the UV region. Finally, a trap-assisted Poole–Frenkel effect-based energy bandgap mechanism, that allows the defect level formed by lattice mismatch between the substrate and GaN to be used as an electron carrier path, is newly defined. This study will present the direction of future UV PDs by providing a new MW structure based on GaN materials, a third-generation semiconductor.     

Automated Test Generation from Specifications Based on Formal Description Techniques

This paper describes a research result on automatic generation of abstract test cases from formal specifications by applying many related algorithms and techniques such as the testing framework, rural Chinese postman tour and unique input output sequence concepts. In addition, an efficient algorithm for verifying the strong connectivity of the reference finite state machine and the concept of unique event sequence are explained. We made use of several techniques to form an integrated framework for abstract test case generation from LOTOS and SDL specifications. A prototype of the proposed framework has been built with special attention to real protocol in order to generate the executable test cases in an automatic way. The abstract test cases in tree and tabular combined notation (TTCN) language will be applied to the TTCN compiler in order to obtain the executable test cases which are relevant to the industrial application.     

Development of verification and conformance testing tools for a railway signaling communication protocol

Verification and conformance testing for protocol specification, the key part of the protocol development process, are complementary technologies employed to increase confidence that a system will function as stated in its specifications. In this paper, we verify the safety and liveness of the protocol specified for the Labeled Transition System (LTS) by using a model-checking method and implementing the testing tool, which experimentally demonstrates the presence of deadlock and reachability from the initial state to a random state. Implementing the testing tool can use modal mu-calculus to assess whether protocol model properties, presented by modal logic, meet protocol specifications. In addition, we propose a conformance testing tool to check correct implementation of sequences that have been derived by the UIO method from the specification of the protocol being verified. This generating tool uses the C++ language in the Microsoft Windows NT environment.     

A RWA Algorithm for Differentiated Services with QoS Guarantees in the Next Generation Internet based on DWDM Networks

A major challenge in next generation Internet (NGI) backbone networks based on dense-wavelength division multiplexing (DWDM) is the provision of guaranteed quality-of-service (QoS) for a wide variety of multimedia applications. This paper proposes a new routing algorithm called multi-wavelength minimum interference path routing (MW-MIPR) to provide more reliable QoS guarantees by consideration of the potential future network's congestion status. This improves wavelength utilization by choosing a route that does not interfere too much with potential future connection requests. Moreover, we introduce a differentiated routing and wavelength assignment (RWA) mechanism combined with recovery strategy and the proposed MW-MIPR algorithm based on the differentiated service model in the NGI. Simulation results show that the proposed MW-MIPR algorithm achieves a smaller blocking probability than dynamic routing (DR) that yields the best performance among previous RWA algorithms. And we prove that a differentiated RWA combined with a recovery capability together with the proposed routing scheme provides satisfied QoS assurance for each service class in terms of signal quality and survivability.     

Differentiated Wavelength Assignment with QoS Recovery for DWDM Next Generation Internet Backbone Networks

This paper describes a differentiated wavelength assignment strategy for the appropriate allocation of wavelengths on wavelength-routed quality of service (QoS) routes with differentiated QoS class and recovery capabilities. The paper is based on the differentiated MPS services (DMS) model as a framework for optical bandwidth management and the real time provisioning of optical channels in re-configurable transport networks. MPS stands for multi protocol lambda switching which is a functional part of GMPLS (generalized MPLS). We discuss here a QoS recovery scheme at the optical layer, at the MPS layer, and at the IP layer, as related to QoS failure caused by device failures or attack-induced faults in dense-wavelength division multiplexing (DWDM) transport networks. According to the QoS characteristics of wavelength in optical links and the type of used optical cross-connect (OXC) nodes, a differentiated wavelength assignment strategy that considers QoS recovery capability is also described. We point out important problems that should be resolved in the DMS model for optical QoS routing with differentiated wavelength assignment.