• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2C
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• pp.1-9
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• 2005

Code is a set of words. If, for any pair of words in the code, one is not prefix of another, the code is called "Prefix(-Free) Code". The prefix coding problem is, given n, to find an optimal code with the minimum-sum of lengths of n words. As a special case of this, we present a method to find, given language L in some specific classes of regular languages, an optimal code among prefix codes in L. We also show how the structure of optimal codes varies as n grows, using trees.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.3
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• pp.873-889
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• 2014

IP address lookup is very crucial in performance of routers. Several works have been done on prefix caching to enhance the performance of IP address lookup. Since a prefix represents a range of IP addresses, a prefix cache shows better performance than an IP address cache. However, not every prefix is cacheable in itself. In a prefix cache it causes false hit to cache a non-leaf prefix because there is possibly the longer matching prefix in the routing table. Prefix expansion techniques such as complete prefix tree expansion (CPTE) make it possible to cache the non-leaf prefixes as the expanded forms, but it is hard to manage the expanded prefixes. The expanded prefixes sometimes incur a great deal of update overhead in a routing table. We propose a bitmap-based prefix cache (BMCache) to provide low update overhead as well as low cache miss ratio. The proposed scheme does not have any expanded prefixes in the routing table, but it can expand a non-leaf prefix using a bitmap on caching time. The trace-driven simulation shows that BMCache has very low miss ratio in spite of its low update overhead compared to other schemes.

• Journal of the Korea Society of Computer and Information
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• v.20 no.12
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• pp.45-52
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• 2015

We propose a hybrid prefix caching scheme to enable high speed IP address lookup. All prefixes loaded in a prefix cache should not be overlapped in address range for correct IP lookup. So, every non-leaf prefix needs to be expanded not so as to be overlapped. The shorter expanded prefix is more preferable because it can cover wider address range just as an single entry in a prefix cache. We exploits advantages of two dynamic prefix expansion techniques, bounded prefix expansion technique and bitmap-based prefix expansion technique. The proposed scheme uses dual bound values whereas just one bound value is used in bounded prefix expansion. Our elaborated technique make the dual bound values be associated with several subtries flexibly using bitmap information, rather than with fixed subtries. We evaluate the performance of the proposed scheme in terms of the average length of the expanded prefixes and cache miss ratio. The experiment results show the proposed scheme has lower cache miss ratio than other previous schemes including both bounded prefix expansion and bitmap-based expansion irrespective of the cache size.

• The KIPS Transactions:PartA
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• v.17A no.5
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• pp.221-228
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• 2010

Since string operations were applied to computational biology, security and search for Internet, various data structures and algorithms for computing efficient string operations have been studied. The all-pairs suffix-prefix matching is to find the longest suffix and prefix among given strings. The matching algorithm is importantly used for fast approximation algorithm to find the shortest superstring, as well as for bio-informatics and data compressions. In this paper, we propose an algorithm to find all-pairs suffix-prefix matching using the suffix array, which takes O($k{\cdot}m$)�� time complexity. The suffix array algorithm is proven to be better than the suffix tree algorithm by showing it takes less time and memory through experiments.

• ETRI Journal
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• v.33 no.3
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• pp.344-354
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• 2011

In this paper, a model is introduced named double relation chains (DRC) based on ordered sets. It is proved that using DRC and special relationships among the members of an alphabet, vectors of this alphabet can be stored and searched in a tree. This idea is general; however, one special application of DRC is the longest prefix matching (LPM) problem in an IP network. Applying the idea of DRC to the LPM problem makes the prefixes comparable like numbers using a pair of w-bit vectors to store at least one and at most w prefixes, where w is the IP address length. This leads to good compression performance. Based on this, two recently introduced structures called coded prefix trees and scalar prefix trees are shown to be specific applications of DRC. They are implementable on balanced trees which cause the node access complexity for prefix search and update procedures to be O(log n) where n is the number of prefixes. As another advantage, the number of node accesses for these procedures does not depend on w. Additionally, they need fewer number of node accesses compared to recent range-based solutions. These structures are applicable on both IPv4 and IPv6, and can be implemented in software or hardware.

• Annual Conference on Human and Language Technology
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• 2021.10a
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• pp.622-624
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• 2021

현재 BERT와 같은 대용량의 코퍼스로부터 학습된 사전 학습 언어 모델을 자연어 응용 태스크에 적용하기 위해 일반적으로 널리 사용되는 방법은 Fine-tuning으로 각 응용 태스크에 적용 시 모델의 모든 파라미터를 조정하기 때문에 모든 파라미터를 조정하는데 필요한 시간적 비용과 함께 업데이트된 파라미터를 저장하기 위한 별도의 저장공간이 요구된다. 언어 모델이 커지면 커질수록 저장 공간의 비용이 증대됨에 따라 이러한 언어모델을 효율적으로 튜닝 할 수 있는 방법들이 연구되었다. 본 연구에서는 문장의 입력 임베딩에 연속적 태스크 특화 벡터인 prefix를 추가하여 해당 prefix와 관련된 파라미터만 튜닝하는 prefix-tuning을 한국어 네이버 감성 분석 데이터 셋에 적용 후 실험결과를 보인다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12C
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• pp.1167-1176
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• 2009

In This Paper, we introduce an efficient IFFT design technique named for transmitter of OFDM (Orthogonal Frequency Division Multiplexing) system. In OFDM system, a cyclic prefix is inserted in forepart of OFDM symbol to prevent ICI(Inter-channel Interference) and ISI (Inter-symbol Interference). Attaching cyclic prefix causes delay in storing and copying IFFT result. The proposed IFFT removes this delay because its output is cyclic shifted by the length of cyclic prefix. So we can make a complete OFDM symbol by just copying the forepart of IFFT output to the end. In many cases, the length of cyclic prefix is 1/2n of FFT size, and this IFFT does not require additional hardware complexity and it does not cause any performance degradation.

• Journal of KIISE:Information Networking
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• v.32 no.4
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• pp.543-550
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• 2005

Demand for better services in the Internet has been increasing due to the rapid growth of the Internet, and hence next generation routers are required to perform intelligent packet classification. For a given classifier defining packet attributes or contents, packet classification is the process of identifying the highest priority rule to which a packet conforms. A notable characteristic of real classifiers is that a packet matches only a small number of distinct source-destination prefix pairs. Therefore, a lot of schemes have been proposed to filter rules based on source and destination prefix pairs. However, most of the schemes are based on sequential one-dimensional searches using trio which requires huge memory. In this paper, we proposea memory-efficient two-dimensional search scheme using source and destination prefix pairs. By constructing binary prefix tree, source prefix search and destination prefix search are simultaneously performed in a binary tree. Moreover, the proposed two-dimensional binary prefix tree does not include any empty internal nodes, and hence memory waste of previous trio-based structures is completely eliminated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.11B
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• pp.911-919
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• 2004

IP address lookup is one of the essential functions on internet routers, and it determines overall router performance. The most important evaluation factor for software-based IP address lookup is the number of the worst case memory accesses. Binary prefix tree (BPT) scheme gives small number of worst case memory accesses among previous software-based schemes. However the tree structure of BPT is normally unbalanced. In this paper, we propose weighted binary prefix tree (WBP) scheme which generates nearly balanced tree, through combining the concept of weight to the BPT generation process. The proposed WBPT gives very small number of worst case memory accesses compared to the previous software-based schemes. Moreover the WBPT requires comparably small size of memory which can be fit within L2 cache for about 30,000 prefixes, and it is rather simple for prefix addition and deletion. Hence the proposed WBPT can be used for software-based If address lookup in practical routers.

• KIPS Transactions on Software and Data Engineering
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• v.2 no.4
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• pp.267-272
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• 2013

As an important operation with many applications such as data cleaning and duplicate detection, the similarity join is a challenging issue, which finds all pairs of records whose similarities are above a given threshold in a dataset. We propose a new algorithm that uses the prefix filtering principle as strong constraints on generation of candidate pairs for fast similarity joins. The candidate pair is generated only when the current prefix token of a probing record shares one prefix token of an indexing record within the constrained prefix tokens by the principle. This generation method needs not to compute an upper bound of the overlap between two records, which results in reduction of execution time. Experimental results show that our algorithm significantly outperforms the previous prefix filtering-based algorithms on real datasets.