Browsing by Author "Peng, Wei-Hao"

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Application classification using packet size distribution and port association
(2009-09-01)
Lin, Ying-Dar
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Lu, Chun-Nan
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Lai, Yuan-Cheng
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Peng, Wei-Hao
;
Lin, Po-Ching
Traffic classification is an essential part in common network management applications such as intrusion detection and network monitoring. Identifying traffic by looking at port numbers is only suitable to well-known applications, while signature-based classification is not applicable to encrypted messages. Our preliminary observation shows that each application has distinct packet size distribution (PSD) of the connections. Therefore, it is feasible to classify traffic by analyzing the variances of packet sizes of the connections without analyzing packet payload. Ill this work, each connection is first transformed into a point in a multi-dimensional space according to its PSD. Then it is compared with the representative points of pre-defined applications and recognized as the application having a minimum distance. Once a connection is identified as a specific application, Port association is used to accelerate the classification by combining it with the other connections of the same session because applications usually use consecutive ports during a session. Using the proposed techniques, packet size distribution and port association, a high accuracy rate, 96% oil average, and low false positive and false negative rates, 4-5%, are achieved. Our proposed method not only works well for encrypted traffic but also can be easily incorporated with a signature-based method to provide better accuracy. (C) 2009 Elsevier Ltd. All rights reserved.
Germanium Possessing Facet-Specific Trap States and Carrier Lifetimes
(2020-06-18)
Tan, Chih-Shan
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Lu, Ming-Yen
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Peng, Wei-Hao
;
Chen, Lih-Juann
;
Huang, Michael H.
Previously, the notable differences in the band structure and changes in bond length and bond distortion between the semiconducting and metal-like planes of germanium have been used to understand the facet-dependent electrical conductivity properties of germanium wafers. To gain further insights into the appearance of electrical facet behaviors, impedance measurements were performed on the Ge{111}, {110}, and {100} wafers. Impedance data and several conductivity-related parameters were used to produce a diagram showing the amount of trap states and the trap state energies. The trap states are found within the germanium band gap with a facet-specific distribution of energies. Compared to the {100} and {110} wafers, the Ge{111} wafer has the lowest trap state density in the probed voltage range. This is consistent with its best conductivity property, as trap states hinder the direct excitation of electrons to the conduction band. Carrier lifetime can also be obtained from the impedance data. The {111} surface generally has the shortest carrier lifetime, which is related to its high electrical conductivity. Interestingly, diffuse reflectance and ultraviolet photoelectron spectral (UPS) measurements yield the smallest Schottky barrier between Ag and the most conductive Ge{111} surface, showing this approach to understanding electrical facet effects can still be useful despite its inadequacy to account for the facet-specific conductivity behaviors of Si wafers. However, one should not rely solely on the experimentally determined Schottky barriers to explain electrical facet effects.