This study presents the design and performance evaluation of a latency bounded and medium access control (MAC) scheme (abbreviated to LB-MAC) for wireless sensor networks that require time-critical communication. LB-MAC provides the predictability for an end-to-sink data delivery time through the time division multiple access (TDMA) multi-channel transmission frame assignment considering the routing path of a tree network. In addition, it uses the traffic-based slot assignment mechanism at every transmission frame to achieve energy efficiency. The feasibility and effectiveness of LB-MAC is demonstrated through extensive simulation based comparisons with prior research.

WiMedia MAC protocol supports fully distributed data communications in high data rate wireless personal area networks (WPANs). WiMedia MAC includes a distributed reservation protocol (DRP) for synchronous traffic and a prioritized contention access (PCA) protocol for asynchronous traffic. Since PCA is based on the carrier-sense multiple access with collision avoidance (CSMA/CA) mechanism, it suffers from low throughput due to collision, especially when the number of devices is large. In this paper, we propose a novel channel access scheme called deterministic channel access (DCA), which determines the transmission order among devices by means of beacon frames. Since all devices follow the deterministic transmission order, collision-free channel access can be achieved and thus the throughput can be significantly improved. Extensive simulation results demonstrate that DCA outperforms PCA in terms of throughput under different situations.

Traffic anomaly detection is one of the most important technologies that should be considered in network security and administration. In this paper, we propose a traffic anomaly detection mechanism that includes traffic monitoring and traffic analysis. We develop an analytical system called WISE-Mon that inspects the traffic behavior by monitoring and analyzing the traffic. We establish a criterion for detecting abnormal traffic by analyzing training set of traffic and applying Fisher linear discriminant method. By using the properties of distributions such as chi-square distribution and normal distribution to the training set, we derive a hyperplane which enables to detect abnormal traffic. Since the trend of traffic can be changed as time passes, the hyperplane has to be updated periodically to reflect the changes. Accordingly, we consider the self-learning algorithm which reflects the trend of traffic and so enables to increase accuracy of detection. The proposed mechanism is reliable for traffic anomaly detection and compatible to real-time detection. For the numerical results, we use a traffic set collected from campus network. It shows that the proposed mechanism is reliable and accurate for detecting the abnormal traffic. Furthermore, it is observed that the proposed mechanism can categorize a set of abnormal traffic into various malicious traffic subsets.

Relay transmission is a promising technology for improving the throughput and energy efficiency in multi-rate wireless personal area networks (WPANs). In this paper, we propose a distributed relay MAC (DR-MAC) protocol in Wi-Media WPANs. DR-MAC extends a distributed reservation protocol (DRP) in WiMedia MAC and neighbor information for relay transmission can be collected during the beacon period. Therefore, DR-MAC can minimize control overhead for relay transmission and is compatible to the standard WiMedia MAC protocol. We also introduce a medium access slot (MAS) allocation procedure for maximizing the efficiency in DR-MAC. Compared with direct transmission, extensive simulation results demonstrate that DR-MAC can improve the throughput by 10% and reduce the energy consumption by 26% when the number of devices is 20.

We have established a medical network in Asia-Pacific area with high-quality moving image on a super broad-banded Internet line since February 2003. Broadcasting real-time surgery and teleconference with medical-quality videos with digital video transport system (DVTS) were so useful to learn surgical techniques and other medical procedures beyond borders. We have conducted 20 events in categories of teleconference (8 times), live transmission of medical procedure (6 times), and remote attendance to scientific medical meetings (6 times) until September 2004. We had teleconferences among 3 countries in APAN-Hawaii in January 2004 (Japan, Korea and USA), and in APAN-Cairns in July 2004 (Japan, Korea and Australia). There have been no serious transmission/ethical problems so far. With these experiences and current achievements, we hope to extend this advanced network system to whole Asia-Pacific countries to share medical skills and knowledge.

We consider the reliable multicast transport protocols used in hybrid networks that include wired and wireless networks and transparent proxy servers in it, which cache multicast packets at the base station and perform local retransmissions across the wireless link. We present two extreme reliable multicast transport protocols, sender-initiated and receiver-initiated, and two analytic performance models supported and unsupported by transparent proxy servers in each reliable multicast protocol, and analyze the throughput of each model. Numerical results show that in any case the protocol with transparent proxy servers effect overall performance more than the one without transparent proxy servers, and furthermore the receiver initiated reliable multicast supported by transparent proxy servers gives better performance of total throughput than the one sender initiated reliable multicast. We provide efficiency criterion of the number of transparent proxy servers for each protocols for varying wireless loss probabilities.

The authors propose a design method for hierarchical crossconnect wavelength-division-multiplexed networks employing a two-stage multiplexing scheme of waveband and wavelength, in order to reduce the complexity and size of optical crossconnect at the nodes. The waveband is formed by grouping lightpaths with the same destination in a network. The authors present an integer linear programming formulation for the routing and grouping of lightpaths, and a heuristic design method is also proposed as a practical method to find a design solution for general large-scale networks. It is found that the proposed design method can largely reduce crossconnect requirements, although it slightly increases the wavelength requirements.

We present an overview of recent research efforts in developing adaptive delivery models for Internet multimedia applications, which dynamically adjust the transmission rate according to network conditions. The proposed mechanism utilizes service priority in multimedia applications. Simulation results show that the average rate of quality degradation increases as utilization increases. However, the degradation rate should be weighted against the increased handoff blocking probability, as priority is assigned to each channel within the permitted range that meets the traffic needs of each channel. The handoff dropping probability is reduced, in situations where resources were highly utilized, by the proposed mechanism.

In the mobile/wireless IP network where frequent mobility is encountered, it is required to accommodate Internet quality of service (QoS) mechanisms such as differentiated services (DiffServ) for mobile hosts. We consider the issue of integration of mobile IP and DiffServ including handoff condition and propose the schemes with a hierarchical agent architecture for supporting QoS in mobile/wireless IP networks. To support DiffServ for mobile hosts, we configure foreign agent to have pre-allocated resources in advance for static service level agreement (SLA) case. In case foreign network has no pre-configured SLA or enough resources for mobile host, we configure new SLA among bandwidth brokers to be set up using dynamic SLA. Also, we propose the signaling and data procedures with DiffServ with respect to fast handoff.

We consider the simulcasting system using distributed antennas in the DS-CDMA system. The simulcasting system in which the same signal is broadcasted simultaneously by distributed antenna ports in a cell can reduce both the blocking probability of a call in a shadowing region and the handoff attempt rate. We propose a controlled distributed antenna system to improve the Eb/Io in both links of the DS-CDMA simulcasting system. It is shown by simulation that improvement in the forward link Eb/Io can be achieved if the ERPs of those ports located far from the considered mobile are reduced to eliminate unwanted interferences to other mobiles. It is also shown that the reverse link Eb/Io can be improved by selection diversity combining.