• Journal of KIISE:Information Networking
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• v.31 no.1
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• pp.20-26
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• 2004

A congestion control algorithm to prevent buffer overflow in MSR(Mobility Support Router) for I-TCP is proposed. Due to high bit error rate and frequent hand-offs over wireless environment, the current congestion control scheme in TCP Reno over mixed(wired and wireless) network exhibits lower throughput than the throughput achieved over wired only network. I-TCP has been proposed to address this by splitting a TCP connection into two TCP connections over wired section and wireless section, respectively. However, buffer overflow in MSR may occur whenever there are excessive bit errors or frequent hand-offs. This may lead to the loss of packets acked by MSR(resident in buffer) to the sender, but not received by the receiver, breaking TCP end-to-end semantics. In this Paper, a new scheme is proposed to prevent the MSR buffer from overflow by introducing “flow control” between the sender and the MSR. Advertised window for the TCP connection between the sender and the MSR is tied to the remaining MSR buffer space, controlling the flow of packets to the MSR buffer before overflow occurs.

• Journal of KIISE:Information Networking
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• v.33 no.5
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• pp.355-368
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• 2006

This paper introduces a new split-TCP approach for improving TCP performance over IEEE 802.11-based wireless LANs. TCP over wireless LANs differently from wired networks is not aggressive, which is a fundamental reason for poor performance. Therefore, we propose TAS (TCP-Aware Sub-layer) to migigate this problem. Our scheme extends the split-connection approach that divides a connection into two different connections at a split point such as an access point (AP). Using TAS, a wireless node emulates TCP ACK packets using MAC ACK frames, instead of receiving real TCP ACK packets. We compared TAS with both normal TCP and I-TCP (Indirect TCP) by NS2 simulation. Results show that TAS achieves higher throughput, more fair resource allocation and, in power-saving mode, shorter delays.

• Journal of the Korea Society of Computer and Information
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• v.25 no.6
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• pp.1-8
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• 2020

Communication between system modules is applied using the Modbus protocol in industrial sites including smart factories, industrial drones, building energy management systems, PLCs, ships, trains, and airplanes. The existing Modbus was used for serial communication, but the recent Modbus protocol is used for TCP/IP communication.The Modbus protocol supports RTU, TCP and ASCII, and implements and uses protocols in embedded systems. However, the transmission I/O devices for RTU, TCP, and ASCII-based protocols may differ. For example, RTU and ASCII communications transmit on a serial-based communication protocol, but in some cases, Ethernet TCP/IP transmission is required. In particular, since the C language (object-oriented) is used in embedded systems, the complexity of source code related to I/O registers increases. In this study, we designed software that can logically separate I/O functions from embedded devices, and designed the execution logic of each instance requiring I/O processing through a delegate class instance with Modbus RTU, TCP, and ASCII protocol generation. We designed and experimented with software that can separate communication I/O processing and logical execution logic for each instance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5B
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• pp.465-475
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• 2004

Transport Control Protocol (TCP) has been implemented in software running on CPU in end systems, and the protocol processing has appeared as a new bottleneck due to advanced link technology. TCP processing is a critical issue in Storage Area Network (SAN) such as iSCSL, and the overall performance of the Storage Area Network heavily depends on speed of TCP processing. TCP Engine implemented in hardware reduces the load of CPU in end systems as well as accelerates the protocol processing, and hence high speed data processing is achieved. In this paper, we have proposed a hardware engine for TCP processing. TCP engine consists of three major block, TCP Connection block Rx TCP block and Tx TCP block TCP Connection block is responsible for managing TCP connection states. Rx TCP block is responsible for receive flow which receives packets from network and sends to CPU. Rx TCP performs header and data processing and sends header information to TCP connection block and Tx TCP block It also assembles out-of-ordered data to in-ordered before it transfers data to CPU. Tx TCP block is responsible for transmit flow which transfers data from CPU to network. Tx TCP performs retransmission for reliable data transfer and management of transmit window and sequence number. Various test-cases are used to verify the TCP functions. The TCP Engine is synthesized using 0.18 micron technology and results in 51K gates not including buffers for temporal data storage.

• Journal of Information Processing Systems
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• v.12 no.1
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• pp.73-82
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• 2016

In cognitive radio networks (CRNs), the performance of the transmission control protocol (TCP) at the secondary user (SU) severely drops due to the mistrigger of congestion control. A long disruption is caused by the transmission of primary user, leading to the mistrigger. In this paper, we propose a cross-layer approach, called a CR-aware scheme that enhances TCP performance at the SU. The scheme is a sender side addition to the standard TCP (i.e., TCP-NewReno), and utilizes an explicit cross-layer signal delivered from a physical (or link) layer and the signal gives an indication of detecting the primary transmission (i.e., transmission of the primary user). We evaluated our scheme by implementing it onto a software radio platform, the Universal Software Radio Peripheral (USRP), where many parts of lower layer operations (i.e., operations in a link or physical layer) run as user processes. In our implementation, we ran our CR-aware scheme over IEEE 802.15.4. Furthermore, for the purpose of comparison, we implemented a selective ACK-based local recovery scheme that helps TCP isolate congestive loss from a random loss in a wireless section.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.88-90
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• 2001

인터넷 정보가전이란 유.무선 정보통신망에 연결되어 데이터 송.수신이 가능한 디지털 TV, 인터넷 냉장고 DVD 디지털 비디오 등과 같은 차세대 가전제품을 말하며, 휴대 정보 단말기로 원격 제어하는 홈 시큐리티 기능뿐만 아니라 초고속 인터넷과 연결되어 영화, 음악, 부가정보 등을 전송 받을 수 있어 향후 정보화 사회의 핵심분야로 부각되고 있다. 본 논문에서는 iRTOS$^{TM}$가 인터넷 정보 가전에 응용될 수 있도록 TCP/IP 네트워크 부분을 설계하고 이를 구현한 내용에 대해 기술한다.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.518-528
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• 2009

IEEE 802.11 wireless local area network (WLAN) has become the prevailing solution for wireless Internet access while transport control protocol (TCP) is the dominant transport-layer protocol in the Internet. It is known that, in an infrastructure-based WLAN with multiple stations carrying long-lived TCP flows, the number of TCP stations that are actively contending to access the wireless channel remains very small. Hence, the aggregate TCP throughput is basically independent of the total number of TCP stations. This phenomenon is due to the closed-loop nature of TCP flow control and the bottleneck downlink (i.e., access point-to-station) transmissions in infrastructure-based WLANs. In this paper, we develop a comprehensive analytical model to study TCP dynamics in infrastructure-based 802.11 WLANs. We calculate the average number of active TCP stations and the aggregate TCP throughput using our model for given total number of TCP stations and the maximum TCP receive window size. We find out that the default minimum contention window sizes specified in the standards (i.e., 31 and 15 for 802.11b and 802.11a, respectively) are not optimal in terms of TCP throughput maximization. Via ns-2 simulation, we verify the correctness of our analytical model and study the effects of some of the simplifying assumptions employed in the model. Simulation results show that our model is reasonably accurate, particularly when the wireline delay is small and/or the packet loss rate is low.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11B
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• pp.953-959
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• 2006

This paper provides optimum TCP/IP packet size that maximizes the throughput efficiency of ATM layer as a function of TCP/IP packet length for several values of channel BER over wireless ATM LAN links applying data link error control schemes to reduce error problems encountered in using wireless links. For TCP/IP delay-insensitive traffc requiring reliable delivery, it is necessary to adopt data link layer ARQ protocol. So ARQ error control schemes considered in this paper include GBN ARQ, SR ARQ and type-I Hybrid ARQ, which ARQ is needed, but FEC can be used to reduce the number of retransmissions. Especially adaptive type-I Hybrid ARQ scheme is necessary for a variable channel condition to make the physical layer as SONET-like as possible.

• Journal of Life Science
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• v.28 no.10
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• pp.1220-1232
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• 2018

The purpose of this animal study was to evaluate, by histological analysis, bone regeneration in rabbit maxillary sinuses with an anorganic bovine graft (Bio-Oss) and a ${\beta}-tricalcium$ phosphate (${\beta}-TCP$) grafting. Bilateral sinus augmentation procedures were performed in 12 adult male rabbits. Rectangular replaceable bony windows were made with a piezoelectric thin saw insert. In the Bio-Oss group, Bio-Oss was grafted and in the ${\beta}-TCP$ group, ${\beta}-TCP$ was grafted and covered by replaceable bony windows. The animals were sacrificed at 2, 4, and 8 weeks after the surgical procedure. The augmented sinuses were evaluated by histomorphometric analysis using hematoxylin-eosin, Masson trichrome, and tartrate-resistant acid phosphatase stains and also by immunohistochemical analysis of proliferating cell nuclear antigen (PCNA), type I collagen, and osteocalcin content. Histologically, new bone formation was found on the surface of Bio-Oss and ${\beta}-TCP$ particles from 2 weeks and continued to 8 weeks. Significant higher new bone formation was revealed in the ${\beta}-TCP$ group than in the Bio-Oss group at 8 weeks. The amount of graft materials was significantly decreased in the ${\beta}-TCP$ group and the number of osteoclasts was significantly increased in the ${\beta}-TCP$ group from 4 to 8 weeks. Immunoreactivity to PCNA was reduced at 8 weeks. The expression of type I collagen was significantly increased in the ${\beta}-TCP$ group at 2 weeks, but was significantly increased in the Bio-Oss group at 8 weeks. Immunoreactivity to osteocalcin was increased from 2 to 8 weeks. These histological results can help in the selection of graft materials for implants. Both Bio-Oss and ${\beta}-TCP$ are proven graft materials, however, these results indicate that ${\beta}-TCP$ showed better bone regeneration results in rabbit maxillary sinus augmentation.

• Journal of the Korea Society of Computer and Information
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• v.14 no.9
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• pp.55-66
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• 2009

In this paper, I will discuss how the Internet has spread rapidly in our lives. Large portals and social networks experience service attacks that access personal customers' databases. This interferes with normal service through DDoS (Distribute Denial of Service Attack), which is the topic I want to discuss. Among the types of DDoS, TCP SYN Flooding attacks are rarely found because they use few traffics and its attacking type is regular transaction. The purpose of this study is to find and suggest the method for accurate detection of the attacks. Through the analysis of TCP SYN Flooding attacks, we find that these attacks cause Backscatter effect. This study is about the algorithm which detects the attacks of TCP SYN Flooding by the study of Backscatter effect.