Sung-Hyung Lee

Design of Authentication Protocol for LR-WPAN using Pre-Authentication Mechanism

This paper proposes a new authentication protocol for the LR-WPAN. In order to guarantee the reliability and safety of a protocol, this protocol uses the hierarchical authentication. In addition, in order to reduce the impact of the denial of service attack, the proposed protocol performs the authentication between a parent router and a joiner device prior to the authentication between a trust center and the joiner device. Moreover, this protocol reduces the authentication delay by decreasing the number of message exchanges during authentication. We evaluate the safety of the proposed protocol by the security analysis and compare the number of message exchanges of the ZigBee authentication protocol and the proposed protocol when denial of service attack occurs. We also analyze the delay for authentication of the joiner device through the implementation of both protocols. Those results show that the proposed protocol effectively protects networks from the denial of service attack and reduces the time for authenticating the joiner device up to maximum 30% as the number of hops increases.

Active Buffer Management Algorithm for Voice Communication System with Silence Suppression

This paper proposes silence drop first(SDF) active buffer management algorithm to increase the voice capacity when silence suppression is used. This algorithm finds and drops silence packet rather than voice packet in the queue for resolving buffer overflow of queue. Simulations with voice codec of G.729A and G.711 are performed. By using proposed SDF algorithm, the voice capacity is increased by 84.21% with G.729A and 38.46% with G.711. Further more, SDF algorithm reduces the required link capacity and loosens the silence packet inter-arrival time limit to provide target voice quality compared with that of conventional algorithms.

Correlation of human papilloma virus status with quantitative perfusion/diffusion/metabolic imaging parameters in the oral cavity and oropharyngeal squamous cell carcinoma: comparison of primary tumour sites and metastatic lymph nodes

AIM To investigate the differences in perfusion/diffusion/metabolic imaging parameters according to human papilloma virus (HPV) status in the oral cavity and oropharyngeal squamous cell carcinoma (OC-OPSCC), separately in primary tumour sites and metastatic lymph nodes. MATERIALS AND METHODS This retrospective study comprised 41 patients with primary OC-OPSCCs and 29 patients with metastatic lymph nodes. The perfusion/diffusion/metabolic imaging parameters were measured at the primary tumour and the largest ipsilateral metastatic lymph node. The quantitative parameters were compared between the HPV-positive and -negative groups. RESULTS The HPV-positivity was 39% (16 patients) for the primary tumours and 51.7% (15 patients) for the metastatic lymph nodes. Patients with HPV-positive tumours had a lower T stage (p=0.034). The metastatic lymph nodes for the HPV-positive patients were bulkier (p=0.016) and more frequently had cystic morphology (p=0.005). The perfusion parameters were not different, regardless of HPV status. The diffusion parameter (ADCmin, p=0.011) of the metastatic lymph nodes in the HPV-positive groups was lower and metabolic parameter (metabolic tumour volume p=0.035 and total lesion glycolysis p=0.037) were higher than those in HPV-negative groups. CONCLUSION The diffusion and metabolic parameters of metastatic lymph nodes from OC-OPSCC were different according to HPV status. The perfusion parameters did not clearly represent HPV status.

Performance evaluation of random access response estimation scheme for IoT communications

This paper analyzed the performance of the LTE random access (RA). We describes a RA performance analysis simulator for LTE to support massive number of devices. To evaluate the performance, we developed new modules to simulate LTEs RA procedures because there is a limit when it accommodate massive number of devices in existing LTE module. This paper also represents performance analysis results according to the number of preambles and maximum number of preamble transmissions in the same environment with 3GPP TR 37.868. With this results, we proposed the random access response (RAR) estimation scheme. As a result, the performance of RA is greatly improved compared to conventional RA.

Adaptation for the retransmission in VoIP applications

An adaptive retransmission scheme can be used for voice over Internet protocol services to provide a certain level of quality of service. However, parameters used for adaptive retransmission must be selected carefully due to unintended frame loss in the channel and in the playout buffer. In this paper, we evaluate the frame loss rate (FLR) in the output of playout buffer for the adaptive retransmission. This paper also proposes a parameter selection algorithm based on the evaluation. The proposed algorithm controls the probability of starting the retransmission process and the maximum number of retransmissions considering a bursty channel model and the loss in the playout buffer. The evaluation results show that the proposed scheme can select the proper parameters to provide a desired FLR in the output of the playout buffer. In addition, the measured mean opinion score-listening quality objective, which is an expected objective quality score, also shows that the proposed algorithm has a potential to provide a desired level of quality score.