WoongChul Choi

A Reliable Multicast MAC Protocol Using Busy-Tone for the IEEE 802.11-Based Wireless Networks

Various application services including multimedia applications need efficient multicast technologies, but the IEEE 802.11 protocol, which is currently the most widely used, does not specify the standard on multicast, which is, instead, substituted by broadcast or a combination of unicast. Using broadcast is, however, difficult to judge on the transmission success or fail, because it does not receive acknowledgements for each data transmission. Using unicast, on the other hand, has problems of transmission delay or bandwidth waste due to the duplicate transmission or retransmission. This paper proposes a RBMAC that guarantees a reliable multicast and improves the throughput by using busy-tone. The proposed RBMAC is implemented in the ns-2 simulator and performed various comparisons with the multicast with IEEE 802.11 MAC. The simulation results show that the proposed RBMAC improves the throughput as much as 20% and the receiving rate by up to 49%.

Simulation and Implementation of Voice-Over-IEEE 802.15.4 LR-WPAN

The IEEE 802.15.4 LR-WPAN specifies low cost, low energy, low rate transmission of 20~250 kbps and mostly within 10 meters of diameter. Its specification of PHY and MAC layers can be used as the lower layers of ZigBee technology. As many applications for short range, wireless networking environment have been developed, the need for voice transmission over the IEEE 802.15.4 LR-WPAN has been also increased. This paper studies the possibility and effectiveness of voice transmission over the IEEE 802.15.4 LR-WPAN by intensive simulations using ns-2 simulator, and shows several use cases as its applications by their implementations.

A Novel GTS Mechanism for Reliable Multihop Transmission in the IEEE 802.15.4 Network

The IEEE 802.15.4 standard provides Guaranteed Time Slot (GTS) mechanism for reliable transmission. GTS mechanism is suitable for transmitting time-sensitive data because it allocates time slots to a specific node. However, the GTS mechanism in the standard can be used only for one-hop communication. This paper proposes and implements a multihop GTS mechanism for reliable transmission in multihop networks. Simulation results using NS-2 show that low delay and high delivery ratio can be achieved using the proposed mechanism.

Assessment of IT Governance of COBIT Framework

The IT governance has been drawn much attention, and the COBIT has been known as a framework for the IT governance. One of the key features of the IT governance is the alignment of business goals and IT goals. The COBIT framework basically provides the definitions of business, IT and processes’ goals and the links among them. There has been much research on the assessment of the IT governance in terms of applying the COBIT framework to the IT governance of an organization. However, this paper studies the assessment of the IT governance of the COBIT framework itself. We develop an assessment method, apply it to the COBIT framework and derive several assessment results including the weights of the IT goals and the IT processes to the business goal. The results can also be applied to other IT governance areas such as the priority determination of the IT investment or IT audit.

Design of anonymity-preserving user authentication and key agreement protocol for ubiquitous computing environments

The spread of mobile devices, PDAs and sensors enabled the construction of ubiquitous computing environments, transforming regular physical spaces into “Smart space” augmented with intelligence and enhanced with services. However, the deployment of this computing paradigm in real-life is disturbed by poor security, particularly, the lack or proper authentication, authorization and key management techniques. Also, it is very important not only to find security measures but also to preserve user privacy in ubiquitous computing environment. In this paper, we propose efficient user authentication and key agreement protocol with anonymity for the privacy-preserving for ubiquitous computing environments. Our scheme is suitable for distributed environments with the computational constrained devices by using MAC-based security association token.

An EJB-based platform for policy-based qos management of diffserv enabled next generation networks

Unlike IntServ where resource reservation and admission control is per-flow based using RSVP, DiffServ supports aggregated traffic classes to provide various QoS to different classes of traffics. However, it is possible to lead to serious QoS violations without a QoS management support. Therefore, a QoS management system that can manage differentiated QoS provisioning is required. This paper proposes and implements a policy-based QoS management platform for differentiated services networks, which specifies QoS policies to guarantee dynamic QoS requirements. High-level QoS policies are represented as valid XML documents and are mapped into EJB beans of the EJB-based policy server of the platform. The policy distribution and the QoS monitoring are processed using SNMP.

WFCTA (weighted fair channel time allocation) and its analysis for HR-WPAN

The IEEE 802.15.3 standard does not specify how to schedule CTA (Channel Time Allocation)s in CTAP (Channel Time Allocation Period) of a superframe. In this paper, we propose a novel scheduling algorithm for channel time allocation of 802.15.3-based HR-WPAN (High Rate Wireless Personal Area Networks), named WFCTA (Weighted Fair Channel Time Allocation). The proposed WFCTA inherently has properties which are necessary for various QoS provisioning, because it is based on TDMA, applied by WFQ algorithm. We explain and compare four implementation cases of WFCTA. We also analyze its worst-case performance in terms of both link utilization and fairness and verify it by simulation.

BCTMA (bi-directional cut-through medium access) protocol for 802.11-based multi-hop wireless networks

In DCF of 802.11-based multi-hop wireless networks, a channel access sequence of 4-way handshake with RTS-CTS-DATA-ACK is used to forward a single packet. For multi-hop packet forwarding, multiple channel accesses with this 4-way handshake are required, and this might entail multiple collisions, which, in turn, results in poor end-to-end performance. To eliminate the overhead of these multiple channel accesses and, as a result, to reduce the possible number of collisions, the DCMA (Data-driven Cut-through Medium Access) protocol has been proposed[5]. We name the scheme used in the DCMA protocol the forward cut-through scheme. In this paper, we propose BCTMA (Bi-directional Cut-Through Medium Access)protocol for high performance 802.11-based multi-hop wireless networks by combining both forward and backward cut-through schemes. We have implemented BCTMAprotocol in ns-2[9]. We conducted a comprehensive simulation to study the performance improvements. The simulation results indicate that the performance is significantly improved and the number of dropped packets due to collisions can be significantly reduced as much as a half.

Implementation of the IEEE 802.15.4 module with CFP in NS-2

The IEEE 802.15.4 standard, widely used in sensor networks, specifies the CAP (Contention Access Period) and the CFP (Contention Free Period). The devices contend for access to transmission media using the CSMA/CA mechanism in the CAP, while, in the CFP, the devices are allocated the GTS (Guaranteed Time Slot) to access media without contention. Therefore, the CFP is useful for the safe and fast delivery of data packets. In spite of such usefulness and need, the CFP is not implemented in widely used NS-2. This paper presents the issues of the modification and extension for the implementation of the CFP module in NS-2. The simulation is used to validate the implemented module.

Software assurance towards better IT service

Much active research has been done on service science in order to improve productivity, efficiency and customer satisfaction of IT service. If any software application or module in IT service behaves incorrectly, service quality and customer satisfaction will decrease significantly. In order to solve such problems, research on software assurance has been drawn much attention recently. Most widely recognized research has been carried out by various government agencies and research institutes such as DHS, DoD, NIST, NASA, SAFECode, CWE™, and SANS. This paper investigates various research on software assurance and discusses the unconsidered matters that have not been studied or solved yet. Finally, a system for the improved software assurance is proposed.