• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.3
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• pp.534-541
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• 2018

The number of stations existing in the same wireless channel is increasing due to the spread of the wireless LAN devices. CSMA/CA, a conventional wireless LAN protocol, uses a random backoff method. In the random backoff scheme, collision between stations is frequent in a dense region where the number of stations existing in the same channel is several tens or more, and the performance of the performance degradation of such a protocol, the IEEE 802.11ah standard proposed a Restricted Access Window(RAW) wireless access method. RAW improves performance by limiting the number of concurrent access stations by dividing the stations into several groups. In this paper, we propose a method to improve the performance of channel connection by using new group creation, group removal and group relocation algorithm according to traffic change by improving existing RAW method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.7
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• pp.845-851
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• 2019

We design, implement, and evaluate a user-level ad hoc network routing protocol on the COTS (commercial off-the-shelf) mobile devices. In situations such as disaster recovery, emergency communication between mobile devices is necessary. For wide deployability and usability of such a system, we design and implement the networking protocols on the user level instead of modifying the kernel of mobile devices. In order to support reliable data transfer in high mobility scenarios, we selected to implement AODV (Ad Hoc On-Demand Distance Vector) as the routing protocol and TCP as the transport layer protocol. With our implementation of ad hoc networking stack on COTS smartphones, we conducted experiments in various networking environments. Our experimental results show that ad hoc networking is possible in up to 12 hops in a line topology and 5 concurrent devices in a star topology.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8B
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• pp.539-546
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• 2007

For better performance and to avoid member service annoyance that results due to joining-clients' waiting durations and time-outs when there are more than one client wanting to join concurrently for Personal Broadcasting System service, there is a need for improving concurrent member joining mechanism. For a more efficient and better performing, this paper apply Overlay Multicast based mini-Overlay Broadcasting Control Protocol(mOBCP) Algorithm on Personal Broadcasting System. mOBCP proposed is performance-effective mechanism, since it considers the case of how fast will children, concurrently, find and join new parents when paths to existing parents are in Failure. The performance comparison, in terms of tree construction time variation and Latency are done through simulations and the results conclude in favour of the Proposed mOBCP.

• The Transactions of the Korea Information Processing Society
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• v.3 no.6
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• pp.1365-1374
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• 1996

To alleviate the blocking inherent in 2-phase commit protocol(2PC) that is widely used to ensure the atomicity of global transactions in distributed environments, an optimistic 2PC can be used. Under the optimistic 2PC, compensation transactions are introduced to ensure the atomicity of transactions, which may result in the violation of global serializability due to the properties of compensation, transactions. In this paper, we propose several valid management protocols for global transactions to ensure the global serializability through the analysis of transaction of state transitions. To determine the execution of one global transaction, the proposed protocols check the sates of other concurrent global transactions. According to the result, execution of the global transaction may be delayed to ensure the global serializability.

• The Journal of Information Systems
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• v.14 no.3
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• pp.89-96
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• 2005

Though studies on negotiations have actively been conducted in the field of e-Commerce so far, some problems have yet to be solved and many application fields of negotiation systems exist. Currently, many businesses shift from various fields to e-Commerce market, due to recent social changes and expansion of e-Commerce market; however, we need to develop the study of automated agents to resolve the issue of negotiation, which is an essential element in the e-Commerce, by minimizing human interference under the e-Commerce environment. In this study, we intend to propose a new negotiation protocol considering the negotiation alternatives through continuous negotiation rounds in relation to an automated negotiation issue whose participants are one to N (seller to buyers). We also present an agent-facilitated negotiation methodology by which negotiation alternative generation process is automated, in consideration of buyer's negotiation attributes and strategies in the negotiation system.

• Radiation Oncology Journal
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• v.11 no.2
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• pp.355-361
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• 1993

Since May 1991, authors have conducted a pilot study to determine the feasibility and evaluate the effect of concurrent radiation therapy and chemotherapy with 5-FU and Cis-platinum for locally advanced cervical cancer (stage IIB-IVA). Radiation therapy consisted of external irradiation to whole pelvis (4140 cGy/23 fx) in 4.5 weeks followed by high dose rate intracavitary radiation therapy (HDR ICRT) to deliver a dose of 30 to 35 Gy to A point in 6 to 7 fractions. After the intracavitary radiation therapy, parametrial boost was delivered for B point dose of 60 Gy in Stage IIB and 65 Gy in stage IIIB. 5-FU (1000 $mg/m^2/24hr$ for 96 hour iv infusion) and Cis-platinum (20 $mg/m^2/day$ IV bolus for 3 days) were given during the second week of external RT and the second course chemotherapy administered at the first HDR ICRT with the same method as the first chemotherapy. Sixteen patients (10 stage IIB,4 stage IIIB,2 stage IVA) were registered to this protocol. Among these 16 patients, two refused treatment after 2 fractions of external irradiation, and one could not continue intracavitary irradiation because of treatment related genitourinary toxicity. So 14 patients were evaluated for toxicity and 13 patients were evaluated for response analysis. Five of 14 patients developed grade 3 gastrointestinal toxicity but 4 of them recovered at the completion of treatment. One stage IIIB patient with inguinal lymph node metastasis who received higher dose of radiation in spite of initial poor performance status did not recover from gastrointestinal toxicity at the completion of treatment. And she died of distant metastasis at one month after the completion of treatment. Two of 14 evaluable patients showed weight loss, more than $10\%$ of initial weight. One patient developed grade 3 leukopenia. In this study, the average total treatment period of completely treated patients was 75 days and three of them took more than 80 days (84, 84, 89 days). Toxicities were generally acceptable and there were no treatment related death. At the last follow-up, complete response was achieved in $62\%(8/13)$ and especially of nine patients with stage IIB, eight patients showed complete response. This study suggests that concurrent radiation therapy and chemotherapy (5-FU and Cis-platinum) is tolerable and effective. Further follow-up is needed to determine whether this protocol will have a favorable impact on survival and to evaluate the late effect on normal tissues. In future, prospective randomized trials are needed to compare the standard radiation therapy alone with concurrent chemotherapy and radiation therapy for locally advanced cervical carcinoma.

• Radiation Oncology Journal
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• v.36 no.1
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• pp.17-24
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• 2018

Purpose: This study aimed to assess complications and outcomes of a new approach, that is, combining short course radiotherapy (SRT), concurrent and consolidative chemotherapies, and delayed surgery. Materials and Methods: In this single arm phase II prospective clinical trial, patients with T3-4 or N+ M0 rectal adenocarcinoma were enrolled. Patients who received induction chemotherapy or previous pelvic radiotherapy were excluded. Study protocol consisted of three-dimensional conformal SRT (25 Gy in 5 fractions in 1 week) with concurrent and consolidation chemotherapies including capecitabine and oxaliplatin. Total mesorectal excision was done at least 8 weeks after the last fraction of radiotherapy. Primary outcome was complete pathologic response and secondary outcomes were treatment related complications. Results: Thirty-three patients completed the planned preoperative chemoradiation and 26 of them underwent surgery (24 low anterior resection and 2 abdominoperineal resection). Acute proctitis grades 2 and 3 were seen in 11 (33.3%) and 7 (21.2%) patients, respectively. There were no grades 3 and 4 subacute hematologic and non-hematologic (genitourinary and peripheral neuropathy) toxicities and perioperative morbidities such as anastomose leakage. Grade 2 or higher late toxicities were observed among 29.6% of the patients. Complete pathologic response was achieved in 8 (30.8%) patients who underwent surgery. The 3-year overall survival and local control rates were 65% and 94%, respectively. Conclusion: This study showed that SRT combined with concurrent and consolidation chemotherapies followed by delayed surgery is not only feasible and tolerable without significant toxicity but also, associated with promising complete pathologic response rates.

• Journal of KIISE:Databases
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• v.30 no.2
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• pp.209-224
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• 2003

Recent development of electronic commerce enables the use of Electronic Stock Trading Systems(ESTS) to be expanded. In ESTS, information with various sensitivity levels is shared by multiple users with mutually different clearance levels. Therefore, it is necessary to use Multilevel Secure Database Management Systems(MLS/DBMSs) in controlling concurrent execution among multiple transactions. In ESTS, not only analytical OLAP transactions, but also mission critical OLTP transactions are executed concurrently, which causes it difficult to adapt traditional secure transaction management schemes to ESTS environments. In this paper, we propose Secure One Snapshot(SOS) protocol that is devised for Secure Transaction Management in ESTS. By maintaining additional one snapshot as well as working database SOS blocks covert-channel efficiently, enables various real-time transaction management schemes to be adapted with ease, and reduces the length of waiting queue being managed to maintain freshness of data by utilizing the characteristics of less strict correctness criteria. In this paper, we introduce the process of SOS protocol with some examples, and then analyze correctness of devised protocol.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.11
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• pp.5179-5202
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• 2018

Transmission Control Protocol (TCP) is the most widely used protocol in the cloud data centers today. However, cloud data centers using TCP experience many issues as TCP was designed based on the assumption that it would primarily be used in Wide Area Networks (WANs). One of the major issues with TCP in the cloud data centers is the Incast issue. This issue arises because of the many-to-one communication pattern that commonly exists in the modern cloud data centers. In many-to-one communication pattern, multiple senders simultaneously send data to a single receiver. This causes packet loss at the switch buffer which results in TCP throughput collapse that leads to high Flow Completion Time (FCT). Recently, Software-Defined Networking (SDN) has been used by many researchers to mitigate the Incast issue. In this paper, a detailed survey of various SDN based solutions to the Incast issue is carried out. In this survey, various SDN based solutions are classified into four categories i.e. TCP Receive Window based solutions, Tuning TCP Parameters based solutions, Quick Recovery based solutions and Application Layer based solutions. All the solutions are critically evaluated in terms of their principles, advantages, and shortcomings. Another important feature of this survey is to compare various SDN based solutions with respect to different performance metrics e.g. maximum number of concurrent senders supported, calculation of delay at the controller etc. These performance metrics are important for deployment of any SDN based solution in modern cloud data centers. In addition, future research directions are also discussed in this survey that can be explored to design and develop better SDN based solutions to the Incast issue.

• Journal of Korean Institute of Industrial Engineers
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• v.21 no.3
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• pp.441-461
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• 1995

This research proposes an Integrated Product Information Model (IPIM) using STEP (Standard for the Exchange of product model data) for Computer Integrated Manufacturing (CIM) of Concurrent Engineering (CE). IPIM is based on Geometry and Topology (STEP Part 42), Form Feature (STEP Part 48), and Tolerance (STEP Part 48) for representing the integrated information of mechanical parts. For the IPIM, 1) new entities are developed for integration of existing entities, and 2) the existing entities are restructured and modified for a special application protocol. In CIM or CE, the advantages of using IPIM having integrated form of geometry, feature and tolerance are 1) integration of product design, process design and manufacturing sequentially or concurrently. 2) keep the product data consistency, modified by different domain, and 3) automatic data exchange between different application software and different hardware. The prototype system is composed of CAD, Data Probe, DBMS and SDAI (Standard Data Access Interface), and the generated STEP data is stored in a step file of DBMS for other applications.