Sung Un Kim

Verification and conformance test generation of communication protocol for railway signaling systems

Verification and testing are complementary techniques that are used to increase the level of confidence in the correct functioning of communication systems as prescribed by their specifications. This paper presents an experience of model checking for Korean railway signaling protocol specified in LTS (Labeled Transition System). This formal approach checks deadlock, livelock and reachability for the state and action to verify whether properties expressed in modal logic are true on specifications. We also propose a formal method for semi-automated test case generation for Korean railway signaling protocol described in I/O FSM (Input/Output Finite State Machine). This enables the generation of more complete and consistent test sequence for conformance testing. The above functions are implemented by C++ language and included within RSPVTE (Railway Signaling Protocol Verification and Testing Environment) in the MS-windows environment.

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 networks 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.

Control Mechanism for QoS Guaranteed Multicast Service in OVPN over IP/GMPLS over DWDM

OVPN over IP/GMPLS over DWDM technology with QoS assurances is considered as a promising approach for the next generation OVPN. In this paper, we suggest a multicast OLSP (Optical Label Switched Path) establishment mechanism for supporting high bandwidth multicast services in OVPN over IP/GMPLS over DWDM. For the establishment of the multicast OLSP, we propose a new multicast tree generation algorithm VS-MIMR that finds the minimum interference path between virtual source nodes. We also suggest an entire OVPN control mechanism to adapt the operation of the routing and signaling protocols of GMPLS.

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.

Fault/attack tolerant recovery mechanism under SRLG constraint in the next generation optical VPN

A “Virtual Private Network (VPN) over Internet” has the benefits of being cost-effective and flexible. However, given the increasing demands for high bandwidth Internet and for reliable services in a “VPN over Internet,” an IP/GMPLS over DWDM backbone network is regarded as a very favorable approach for the future “Optical VPN (OVPN)” due to the benefits of transparency and high data rate. Nevertheless, OVPN still has survivability issues such that a temporary fault can lose a large amount of data in seconds, moreover unauthorized physical attack can also be made on purpose to eavesdrop the network through physical components. Therefore fault/attack tolerant recovery mechanism that considers physical components is needed because optical network has vulnerabilities involved in the intrinsic characteristics, and these characteristics possibly menace reliable services in OVPN. Thus in this paper, with considering fault/attack in the next generation OVPN, we propose a recovery mechanism under shared risk link group (SRLG) constraint for network survivability by means of the classification of optical components and shared risk levels.

A New Data Aggregation Algorithm for Clustering Distributed Nodes in Sensor Networks

The sensor nodes in sensor networks are limited in power, computational capacities, and memory. In order to fulfill these limitations an appropriate strategy is needed. Data aggregation is one of the power saving strategies in sensor networks, combining the data that comes from many sensor nodes into a set of the meaningful information. This paper proposes a new data aggregation algorithm named DAUCH (Data Aggregation algorithm Using DAG rooted at the Cluster Head) for clustering distributed nodes in sensor networks, combining the random cluster head election technique in LEACH with DAG in TORA. The proposed algorithm outperforms LEACH due to the less transmission power. Our simulation reveals that approximately a 4% improvement is accomplished comparing to the number of nodes alive with LEACH.

Multicast OLSP establishment scheme in OVPN over IP/GMPLS over DWDM

OVPN (Optical Virtual Private Network) over IP (Internet Protocol)/GMPLS (Generalized Multi-Protocol Label Switching) over DWDM (Dense Wavelength Division Multiplexing) technology with QoS assurances is considered as a promising approach for the next generation OVPN. In this paper, we suggest a multicast OLSP (Optical Label Switched Path) establishment mechanism for supporting high bandwidth multicast services. For the establishment of the multicast OLSP, we propose a new multicast tree generation algorithm VS-MIMR (Virtual Source-based Minimum Interference Multicast Routing) that finds the minimum interference path between virtual source nodes. We also suggest an entire OVPN control mechanism to adapt the operation of the routing and signaling protocols of GMPLS.

Survivability-Guaranteed network resiliency methods in DWDM networks

The ability of a network to withstand and recover from failures, survivability, is one of the most important requirements of dense-wavelength division multiplexing (DWDM) networks. And the network resiliency methods through the efficient route computation are critical issues in terms of blocking probability, survivability ratio and service disruption ratio. In this paper, we propose the network resiliency methods used to guarantee survivability by applying shared risk link group (SRLG) and trap avoidance (TA) problem which are important criteria in DWDM networks.

Unicast and multicast RWA algorithms in DWDM-Based OVPN backbone networks

OVPN (Optical Virtual Private Network) based on DWDM (Dense Wavelength Division Multiplexing) backbone framework has been regarded as a favorable approach for the future VPN In DWDM-based OVPN, the RWA (Routing and Wavelength Assignment) problem has been an important and challenge issue for network performance improvements In this paper, we propose new RWA algorithms in both cases of unicast and multicast approaches heading toward minimizing congestion by avoiding interference for requested connections Also, we verify the performance of the proposed algorithms in terms of blocking probability and resource utilization.