Hyunsoo Yoon

Performance analysis of multibuffered packet-switching networks in multiprocessor systems

An analytic model and analytic results for the performance of multibuffered packet-switching interconnection networks in multiprocessor systems are presented. The performance of single-buffered delta networks is first modeled using the state transition diagram of a buffer. The model is then extended to account for multiple buffers. The analytic results for multibuffered delta networks are compared to simulation results. The performance of multibuffered data manipulator networks is analyzed to demonstrate the generality of the model. >

Link stability and route lifetime in ad-hoc wireless networks

Many routing algorithms, proposed for ad-hoc wireless networks, are based on source routing scheme. When a route is broken in source routing, route recovery and maintenance procedures are executed. However these procedures consume many resources. To minimize route breaking, it important to find a route that endures longer time. Shortest path route has short lifetime especially in highly dense ad-hoc wireless networks, and it due to the edge effect discovered in this paper Some routing protocols such as SSA and ABR are considering the link stability and try finding more stable route. In this paper, we will focus on the link stability and the lifetime of a route, and propose link stability comparison models for previously proposed routing algorithms. We will show properties of these models and compare them with local optimal algorithm that finds longest lifetime route at a given time. Finally, we will propose an enhanced link stability estimation model to find a route with longer lifetime.

Mobility support in content centric networks

Content-centric networking (CCN) is designed for efficient dissemination of information. Several architectures are proposed for CCN recently, but mobility issues are not considered sufficiently. We classify traffic types of CCN into real-time and non real-time. We examine mobility problems for each type, and suggest the possible hand-off schemes over CCN. Then, we analyze the delay performance in terms of simulation study. We believe that the proposed schemes can be merged as a part of the CCN easily, since they comply with the inherent nature and rules of the CCN.

Optimal modulation and coding scheme selection in cellular networks with hybrid-ARQ error control

We propose an optimal modulation and coding scheme (MCS) selection criterion for maximizing user throughput in cellular networks. The proposed criterion adopts both the Chase combining and incremental redundancy based hybrid automatic repeat request (HARQ) mechanisms and it selects an MCS level that maximizes the expected throughput which is estimated by considering both the number of transmissions and successful decoding probability in HARQ operation. We also prove that the conventional MCS selection rule is not optimized with mathematical analysis. Through link-level and system-level simulations, we show that the proposed MCS selection criterion yields higher average cell throughput than the conventional MCS selection schemes for slowly varying channels.

The knockout switch under nonuniform traffic

The knockout switch is a nonblocking, high-performance switch suitable for broadband packet switching. It allows packet losses, but the probability of a packet loss can be kept extremely small in a cost-effective way. The performance of the knockout switch was analyzed under uniform traffic. In this paper, we present a new, more general analytic model of the knockout switch, which enables us to evaluate the knockout switch under nonuniform traffic. The new model also incorporates the effects of a concentrator and a shared buffer on the packet loss probability. Numerical results for nonuniform traffic patterns of interest are presented. >

Secure and efficient data retrieval over encrypted data using attribute-based encryption in cloud storage

The cloud storage based information retrieval service is a promising technology that will form a vigorous market in the near future. Although there have been numerous studies proposed about secure data retrieval over encrypted data in cloud services, most of them focus on providing the strict security for the data stored in a third party domain. However, those approaches require stupendous costs centralized on the cloud service provider, which could be a principal impediment to achieve efficient data retrieval in cloud storage. In this paper, we propose an efficient data retrieval scheme using attribute-based encryption. The proposed scheme is best suited for cloud storage systems with massive amount of data. It provides rich expressiveness as regards access control and fast searches with simple comparisons of searching entities. The proposed scheme also guarantees data security and user privacy during the data retrieval process.

On submesh allocation for mesh multicomputers: a best-fit allocation and a virtual submesh allocation for faulty meshes

The submesh allocation problem is to recognize and locate a free submesh that can accommodate a request for a submesh of a specified size. In this paper, we propose a new best-fit submesh allocation strategy for mesh-connected multiprocessor systems. The proposed strategy maintains and uses a free submesh list for an efficient allocation. For an allocation request, the strategy selects the best-fit submesh which causes the least amount of potential processor fragmentation. As many large free submeshes as possible are preserved for later allocations. For this purpose, we introduce a novel function quantifying the degree of potential fragmentation of submeshes. The proposed strategy has the capability of recognizing a complete submesh. We also propose an allocation strategy for faulty meshes which can maintain and allocate virtual submeshes derived from faulty submeshes. Extensive simulation is carried out to compare the proposed strategy with previous strategies. The proposed strategy has the best performance: a 6-50 percent improvement over the previous best strategy.

Grapes: topology-based hierarchical virtual network for peer-to-peer lookup services

Peer-to-peer systems and applications are distributed systems without any centralized control. The core operation in most peer-to-peer systems is efficient location of data items. The current well-known peer-to-peer systems like Napster and Gnutella have scalability problem in location of data items. To solve the scalability problem, some scalable peer-to-peer lookup services show up, such as CAN, Chord, Pastry and Tapestry. In this paper we propose a self organizing hierarchical virtual network infrastructure, called Grapes, for peer-to-peer lookup services. Hierarchical approach of Grapes brings two benefits. First, a node can find data in its subnetwork with the high probability due to the data replication in its subnetwork. Second, the hierarchical structure makes lookup hops shorter than those of the flat one.

New modular multiplication algorithms for fast modular exponentiation

A modular exponentiation is one of the most important operations in public-key cryptography. However, it takes much time because the modular exponentiation deals with very large operands as 512-bit integers. The modular exponentiation is composed of repetition of modular multiplications. Therefore, we can rcducc the execution time of it by reducing thc execution time of each modular multiplication. In this paper, we propose two fast modular multiplication algorithms. One is for modular multiplications between different integers, and the other is for modular squarings. These proposed algorithms require single-precision multiplications fewer than those of Montgomery modular multiplication algorithms by 1/2 and 1/3 times, respectively. Implementing on PC, proposed algorithms reduce execution times by 50% and 30% compared with Montgomery algorithms, respectively.

A Smart Handover Decision Algorithm Using Location Prediction for Hierarchical Macro/Femto-Cell Networks

To reduce the number of unnecessary handover in hierarchical macro/femto-cell networks, it is necessary to avoid macro -> femto cell handovers of temporary femtocell visitors who stay in the femtocell for a relatively short time. In this paper, we propose a smart handover decision algorithm exploiting future mobility pattern prediction scheme to prevent macro -> femto cell handovers of such temporary femtocell visitors. Our simulation result shows that the proposed algorithm effectively reduces the number of unnecessary handovers.