Hyukjoon Lee

Implementation of Third Party Based Call Control Using Parlay Network API in SIP Environment

The communication network is in a transition toward the NGN (Next Generation Networks), which can support both of voice and data at the same time, according to the explosive demand of new services. The NGN allows the third-party application provisioning by defining the networks as layers of Services, Distributed Processing Environment and Transport. The Service layer can further be divided into Application and Service Component layer. In order to realize the third-party application provisioning, the Parlay Group has adopted an open Parlay API approach as an interface between the Application and the Service Component layer. Using Parlay API, the third parties may build and deploy the new applications at the Application layer exploiting the service components within network operators’ domain. In this paper, we presents the implementation details about the two-party call setup and release using the third party service logic based on Parlay API Rel. 3.0., where SIP is used as a signaling protocol in Transport layer.

MRED: a new approach to random early detection

In order to reduce the increasing packet loss rates caused by an exponential increase in network traffic, the IETF (Internet Engineering Task Force) is considering the deployment of active queue management techniques such as RED (random early detection). While active queue management in routers and gateways can potentially reduce packet loss rates in the Internet, this paper has demonstrated the inherent weakness of current techniques and shows that they are ineffective in preventing high loss rates. The inherent problem with these queue management algorithms is that they all use queue lengths as the indicator of the severity of congestion. In order to solve this problem, a new active queue management algorithm called MRED is proposed. MRED computes the packet drop probability based on our heuristic method rather than the simple method used in RED. Using simulation, MRED is shown to perform better than existing queue management schemes.

Cross-Layer Handover Optimization Using Linear Regression Model

With the fast proliferation of mobile Internet, the wireless community has been increasingly looking for a framework that can provide seamless mobility. In this paper, we propose a fast cross-layer handover scheme based on movement prediction in mobile WiMAX environment. Prediction is achieved by linear regression model with keeping track of the signal strength of mobile users. With the help of the prediction, layer-3 handover activities are able to occur prior to layer-2 handover, and therefore, total handover latency can be reduced. The experiments conducted with system parameters and propagation model defined by WiMAX Forum demonstrate that the proposed method predicts the future signal level accurately and reduces the total handover latency.

Supporting handover in an IEEE 802.11p-based wireless access system

The IEEE 802.11p-based wireless access networks are about to be deployed by major highways around the world as one of the main information hauling infrastructure for ITS safety applications. As the most applications of the IEEE 802.11p standard require the delivery of short text-based messages, the standard does not support handover between adjacent Road-side Units (RSUs). However, demand for seamless real-time services such as short video clips of CCTVs on a highway gives rise to support for handover in the IEE 802.11p-based wireless access systems. In this paper, we describe a seamless handover scheme for an IEEE 802.11p-based wireless access system that takes advantage of the fixed-order placement of the RSUs and unidirectional movement of the vehicles along the highways. More specifically, this handover scheme utilizes the IEEE 802.11 disassociation message as to signal the old RSU of an On-broad Units (OBU) departure from its coverage area. The subsequent downstream data frames can be proactively forwarded to the new RSU for delivery to the OBU after its link establishment with the new RSU. Simulation results show superior performance of the proposed scheme compared to a poll-based scheme.

Wireless-adaptation of WWW content over CDMA

Information access through the WWW has become one of the most important applications for mobile clients. However, efficient wireless data connectivity is difficult to achieve due to physical and technological limitations. In this paper, we propose a proxy server architecture that facilitates highly effective latency reduction over the wireless link without modifying any of the existing applications. Based on the capabilities of the client devices, Web browsers, the user preferences, and Web content types, several different levels of wireless-adaptation for Web content are performed. The functions included in the wireless-adaptation are general-purpose lossless data compression, data-type specific lossy compression and re-authoring of HTML documents. We show the improvement in the retrieval time through experiments in which a mobile host accesses the WWW via the proxy architecture over a CDMA cellular network.

Dynamic bandwidth provisioning using ARIMA-based traffic forecasting for Mobile WiMAX

With fast proliferation of QoS-enabled wireless packet networks, need for effective QoS control is increasing. In this paper, we focus on QoS provisioning in Mobile WiMAX access service network (ASN). We investigate a dynamic bandwidth provisioning method that can help to increase resource utilization. Our approach consists of two stages: traffic forecasting, followed by bandwidth provisioning. For the first stage, we use auto-regressive integrated moving average (ARIMA) model to forecast traffic based on online measurement. For the second stage, we use a bandwidth provisioning scheme that allocates bandwidths depending on the traffic forecasting. We modeled our problem as a Fractional Knapsack Problem for which we used a greedy algorithm in order to find an approximate solution. Through simulation studies with real-world data sets, we found that our approach could increase the bandwidth for the real-time traffic class and guarantee adequate service quality for the nonreal-time traffic class as well, while maximizing resource utilization.

A distributed proxy server system for wireless mobile Web service

The transcoding proxy strategy has been widely used as a means to reduce the delay in retrieving Web pages over wireless mobile data networks. However, this strategy has a serious drawback of being a potential point of failure or a bottleneck of the service. We developed a distributed proxy server system in which multiple proxy servers are installed at geographically dispersed locations and share the workloads among themselves by serving mobile hosts within assigned regions. A new handoff (HO) message protocol is proposed to enable handoffs between proxies as the mobile hosts move between regions. With this proxy server handoff protocol a client agent at the mobile host requests a proxy server to initiate handoff processing and two proxy servers synchronize distilled data for a HTTP session disconnected by the handoff.

A Location-Based Interactive Model of Internet of Things and Cloud (IoT-Cloud) for Mobile Cloud Computing Applications

This paper presents a location-based interactive model of Internet of Things (IoT) and cloud integration (IoT-cloud) for mobile cloud computing applications, in comparison with the periodic sensing model. In the latter, sensing collections are performed without awareness of sensing demands. Sensors are required to report their sensing data periodically regardless of whether or not there are demands for their sensing services. This leads to unnecessary energy loss due to redundant transmission. In the proposed model, IoT-cloud provides sensing services on demand based on interest and location of mobile users. By taking advantages of the cloud as a coordinator, sensing scheduling of sensors is controlled by the cloud, which knows when and where mobile users request for sensing services. Therefore, when there is no demand, sensors are put into an inactive mode to save energy. Through extensive analysis and experimental results, we show that the location-based model achieves a significant improvement in terms of network lifetime compared to the periodic model.

Energy efficient operation of cellular network using on/off base stations

To allow rapid growth of the number of base stations, reducing the energy consumption of the stations, as the main energy consumers in cellular networks, has become an important research topic. In this paper, we attempt to find an adaptive cell zooming method to reduce the energy consumption of base stations. The cell zooming mechanism was formulated as an optimization problem with consideration of varying traffic patterns and interference, as well as the service availability of the whole area. Simulations were then conducted to verify the performance of the proposed cell zooming method. The simulations considered varying traffic conditions, both timely and spatially, in traditional 19-cell configuration. The proposed scheme demonstrated reduction of energy consumption of up to 4.72 times for urban environments and 3.78 times for rural environments against traditional static cell operation.

Analysis of the harmonic resonance during energizing the primary restorative transmission systems

Power system restoration following a massive or complete blackout starts with energizing primary restorative transmission systems. During this primary restoration process, unexpected over-voltage may happen due to nonlinear interaction between the unloaded transformer and the transmission system. This is known as the harmonic resonance phenomenon that may cause burning out of transformer or other devices. By now the harmonic resonance has been reported in some extra high voltage systems. This paper reports the possible existence of the harmonic resonance in Korean power system. Analysis of the harmonic over-voltage is presented based on various PSCAD/EMTDC simulations.