JooSeok Song

Contention-based limited deflection routing protocol in optical burst-switched networks

Optical burst switching (OBS) is a very promising switching technology for realization of an economical optical Internet. In OBS networks, when contention occurs at an intermediate switch, two or more bursts that are in contention can be lost because a forwarding path reservation is not made for a burst until a control message for the burst arrives. That is the reason why one of the critical design issues in OBS is finding ways to minimize burst dropping resulting from resource contention. In this paper, we propose and analyze a novel deflection routing protocol, which mitigates and resolves contention with significantly better performance as compared with techniques currently known in the literature. While several variants of the basic deflection routing scheme have been proposed before, they all lacked the ability to determine the alternate route based on clear performance objectives. In this paper, we present an on-demand deflection routing scheme, which sequentially performs the following: 1) based on certain performance criteria, dynamically determines if the burst should be deflection routed or retransmitted from source and 2) if the decision is to deflection route, then the same is done using a path that is based on minimization of a performance measure that combines distance and blocking due to contention. The proposed contention-based limited deflection routing scheme prevents injudicious deflection routing. Our simulation results show that the scheme proposed here has much superior performance both in terms of burst loss probability and increased network throughput. Through analytical and simulation modeling, a number of useful insights into the OBS network protocols and performance are provided.

Design and implementation of wireless PKI technology suitable for mobile phone in mobile-commerce

With the advent of wireless communication and internet protocol, many technologies have been developed to provide mobile phone user with the wireless internet service. Security supporting wireless internet must be guaranteed at same level as the wired security. But PKI (Public Key Infrastructure) which is used for the security of e-commerce in wired internet is not suitable for the mobile phone because of the fundamental limitation of performance such as less memory and less powerful CPU. Therefore, we need to develop a wireless PKI (WPKI) that provides the similar security level as the wired PKI supporting mobile phone. In this paper, we consider why it is difficult to apply the wired PKI technology to the mobile phone and how to cope with these problems. We propose wireless PKI technology and illustrate that implementation result of the proposed wireless PKI technology on the newest mobile phone. We minimize data sizes processed in mobile phone, and optimize protocols for the certificate management and verification between mobile phone and server. This results in the reduced module sizes to be able to install in mobile phone. Hence, the proposed WPKI technology shows that security is in the same level as the wired PKI and all PKI procedures are successfully processed in mobile phone.

Group Connectivity Model for Industrial Wireless Sensor Networks

It is a recent trend to consider wireless sensor networks in harsh industrial environments. With actual deployment of wireless sensor networks, it would be desirable to make a concrete deployment plan regarding connectivities and to place sensors by grouping them according to the planned deployment points, even more in case of targeting multiple objects to be sensed and monitored in harsh environments. The connectedness of groups as well as individual sensors is important specifically for real-time data acquisitions and even more if there are no external communication links among these groups. In this paper, we focus on the connectivity of sensor groups, rather than the individual sensors only, and propose a novel group connectivity model so as to analyze group connectivity and to make a concrete deployment plan of sensor groups with regard to the internal distribution of sensors and group positions. We believe that the proposed model should be useful in planning the deployment of wireless sensor networks in harsh industrial environments where running wires is less practical and also prohibitively expensive.

A time-based key management protocol for wireless sensor networks

It is not easy to achieve secure key establishment in wireless sensor networks without public key cryptography. Many key management protocols have been proposed for the purpose. Among them, LEAP is a simple and elegant protocol that establishes multi-level keys in an efficient way, but its security mainly relies on that of a single initialization key. Though it is assumed that the initial deployment phase is secure and the key is erased from sensor nodes after the initialization in LEAP, the assumption could not be viable for two reasons. First, the same key should be used again for node addition after the initialization phase whereas the new node can be captured before removing the key. Second, the initial deployment of dense networks may not take short as LEAP expected in many cases. This paper rethinks the security of LEAP and proposes a more secure scheme with a new notion of probabilistic time intervals. Rather we localize the impact of key compromise within the time intervals.

An adaptable and reliable authentication protocol for communication networks

We propose a new authentication and key distribution protocol which is adaptable and reliable for communication networks. The secrets for authentication, which are chosen from a relatively small space by common users, are easy to guess. Our protocol gives a solution to protect the weak secrets from guessing attacks. Compared with other related work, our protocol is more reliable because it is resistant to various kinds of attacks including guessing attacks, and more adaptable because it reduces several overheads which make the existing protocols more expensive. We show how to apply our protocol to the Q.931 calling sequences and to the World Wide Web model.

Novel defense mechanism against data flooding attacks in wireless ad hoc networks

Mobile users like to use their own consumer electronic devices anywhere and at anytime to access multimedia data. Hence, we expect that wireless ad hoc networks will be widely used in the near future since these networks form the topology with low cost on the fly. However, consumer electronic devices generally operate on limited battery power and therefore are vulnerable to security threats like data flooding attacks. The data flooding attack causes Denial of Service (DoS) attacks by flooding many data packets. However, there are a few existing defense systems against data flooding attacks. Moreover, the existing schemes may not guarantee the Quality of Service (QoS) of burst traffic since multimedia data are usually burst. Therefore, we propose a novel defense mechanism against data flooding attacks with the aim of enhancing the throughput. The simulation results show that the proposed scheme enhances the throughput of burst traffic.

Location-based pairwise key predistribution for wireless sensor networks

A practical pairwise key distribution scheme is necessary for wireless sensor networks since sensor nodes are susceptible to physical capture and constrained in their resources. In this paper, we investigate a simple and practical scheme that achieves higher connectivities and perfect resilience with less resources, even in case of deployment errors.

Phase formation and control of morphology in sputtered Cu–In alloy layers

Abstract The dependence of structural properties and surface morphology of Cu–In alloy layers on the composition and sputtering deposition sequence were investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The properties of the co-sputtered alloy layers changed abruptly around the composition boundary when the Cu/In ratio reached 1/2. This can be explained by the effective heat of formation (EHF) model, which has been used to predict the sequence of phase formation for metal diffusion couples. The use of a co-sputtered alloy layer with a high In concentration was not suitable for fabricating solar cells, because the film had a very rough morphology due to large In islands formed on the CuIn2 phase. However, it was possible to minimize this phase by In sputtering followed by co-sputtering with a Cu/In ratio of 1 (Cu–In/In/Glass). This permitted the fabrication of a homogeneous Cu–In alloy layer, which was not possible through the simple co-sputtering.

An energy-efficient interface selection for multi-mode terminals by utilizing out-of-band paging channels

With the advent of a number of wireless network technologies such as WCDMA and WLAN, current mobiles are equipped with multiple network interfaces, so called Multi-Mode Terminal (MMT). MMTs are capable to access different kinds of networks by performing a vertical handover between heterogeneous wireless networks, where during the idle state, the MMTs consume a lot of energy since their WLAN interface must wake up for listening to periodical beacons. However, previous studies on the vertical handover did not address how to select the optimal interface taking into account the characteristics of MMTs, especially energy consumption. Therefore, in this paper, we propose an energy-efficient interface selection scheme for MMTs in the integrated WLAN and cellular networks. The proposed interface selection scheme takes advantage of existing out-of-band paging channel of cellular networks, so that the WLAN interface can be completely turned off during the idle state leading to reduction in energy consumption. Simulation results show that the proposed scheme outperforms conventional approaches in terms of energy consumption with reduced signaling overhead and handover delay.

A model for embedding and authorizing digital signatures in printed documents

It is a desirable feature in a public key infrastructure (PKI) to include the signature information in a printed document for authenticity and integrity checks, in a way to bind an electronic document to the printed document. However, it is not easy to preserve the digital signature in the printed document because the digital signature is for the text code (or the whole document file), not for the text image (which can be scanned optically) in printed form. So, we propose a practical and secure method for preserving the authorized digital signatures for printed documents. We will derive a printable digital signature scheme from the Korean Certificate-based Digital Signature Algorithm (KCDSA) for secure transaction and utilize the dense two-dimensional barcode, QRcode, for printing out the signature and data in a small area within a printed document.