• Journal of Internet Computing and Services
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• v.2 no.2
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• pp.65-70
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• 2001

In this paper, a Modified RED algorithm for congestion avoidance in IP networks is presented. The RED detects incipient congestion by computing the average queue size. By notifying only a randomly selected fraction of connection, it causes to the global synchronization or fairness problem, And also, the network characteristics need to be known in order to find th optimum average queue length. When the average queue size exceeds a minimum threshold, a modified RED algorithm drops packets based on the state of each connection. Performance is improved because of keeping the average queue size low while allowing occasional bursts of packets in the queue, we compare performance of modified RED with RED and Drop Tail in terms of goodput, network utilization and fairness.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.2 no.6
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• pp.333-351
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• 2008

Transmission control protocols have to overcome common problems in wireless networks. TCP employing both packet loss discrimination mechanism and available bandwidth estimation algorithm, known as the good existing solution, shows significant performance enhancement in wireless networks. For instance, TCP New Jersey which exhibits high throughput in wireless networks intends to improve TCP performance by using available bandwidth estimation and congestion warning. Even though it achieves 17% and 85% improvements in terms of goodput over TCP Westwood and TCP Reno, respectively, we further improve it by exploring maximized available bandwidth estimation, handling bit-error-rate error recovery, and effective adjustment of sending rate for retransmission timeout. Hence, we propose TCP NJ+, showing that for up to 5% packet loss rate, it outperforms other TCP variants by 19% to 104% in terms of goodput when the network is in bi-directional background traffic.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.9
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• pp.12-19
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• 2002

Guaranteed Frame Rate(GFR) service is intended to efficiently support TCP/IP traffic in ATM networks. The GFR service not only guarantees a minimum service rate at the frame level, but also supports a fair share of available bandwidth. The original GFR proposal outlined two switch implementation scheme : FIFO Queuing and perVC-Queuing. In general, it has been shown that FIFO Queuing is not sufficient to provide rate guarantees and perVC-Queuing with scheduling is needed. In perVC-Queuing implementation, scheduling algorithm plays key rule to provide rate guarantees and to improve fairness. We proposed a new scheduling algorithm for the GFR service. Proposed algorithm can provide minimum service rate guarantee and fair sharing to GFR VCs. Computer simulation results show that proposed scheduling scheme provide a much better performance in TCP Goodput and fairness than previous scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3B
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• pp.304-310
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• 2009

In this paper, we evaluate the performance of VoIP in OFDMA-based relay systems with various capabilities of relays. We classify relays according to capability as "mid-capability (MC)" and "high-capability (HC)" relay. In system with HC relays, not only base station (BS) but also relay station (RS) performs scheduling at its ova whereas only BS performs scheduling in system with MC relays using the information reported by MS (i.e. the received signal-to-interference-plus-noise ratio (SINR) of mobile station (HS), the amount of MS traffic, etc). In system with MC relays, the controling overhead of BS is larger than that of system with HC relays. However, since BS has all MS information, efficient resource allocation and scheduling is possible. We derived the "average packet delay," "good packet ratio," and "cell goodput" in a VoIP environment. The simulation results demonstrate that the system with MC relays has better VoIP performance over that with HC relays.

• KIPS Transactions on Computer and Communication Systems
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• v.8 no.8
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• pp.201-208
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• 2019

Intra-Body Communication (IBC) is a communication method using the human body as a communication medium. The fact that our human body consists of water and electrolyte allow such communication method could work and have strength in low-power. However, because the IBC directly affects to human body by using it as a medium, there was a lack of research in communication protocols of each communication layer. In this paper, we suggests MAC parameters which affects the performance of communication in human body channel, and propose new MAC protocol. Our results shows that our MAC is suitable for supporting high data rate applications with comparable radio duty cycle performance.

• International Journal of Computer Science & Network Security
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• v.22 no.10
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• pp.191-200
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• 2022

Constrained Application Protocol (CoAP) is a standardized protocol by the Internet Engineering Task Force (IETF) for the Internet of things (IoT). IoT devices have limited computation power, memory, and connectivity capabilities. One of the significant problems in IoT networks is congestion control. The CoAP standard has an exponential backoff congestion control mechanism, which may not be adequate for all IoT applications. Each IoT application would have different characteristics, requiring a novel algorithm to handle congestion in the IoT network. Unnecessary retransmissions, and packet collisions, caused due to lossy links and higher packet error rates, lead to congestion in the IoT network. This paper presents an adaptive congestion control protocol for CoAP, Adaptive Congestion Control with a Backoff algorithm (ACCB). AACB is an extension to our earlier protocol AdCoCoA. The proposed algorithm estimates RTT, RTTVAR, and RTO using dynamic factors instead of fixed values. Also, the backoff mechanism has dynamic factors to estimate the RTO value on retransmissions. This dynamic adaptation helps to improve CoAP performance and reduce retransmissions. The results show ACCB has significantly higher goodput (49.5%, 436.5%, 312.7%), packet delivery ratio (10.1%, 56%, 23.3%), and transmission rate (37.7%, 265%, 175.3%); compare to CoAP, CoCoA+ and AdCoCoA respectively in linear scenario. The results show ACCB has significantly higher goodput (60.5%, 482%,202.1%), packet delivery ratio (7.6%, 60.6%, 26%), and transmission rate (40.9%, 284%, 146.45%); compare to CoAP, CoCoA+ and AdCoCoA respectively in random walk scenario. ACCB has similar retransmission index compare to CoAp, CoCoA+ and AdCoCoA respectively in both the scenarios.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.9-12
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• 2000

Today, QoS is one of the most critical issues in the network research area and Differentiated Services (DiffServ) is considered as the most prominent solution to provide some kinds of service differentiation without introducing any scalability problem. Among DiffServ's approaches, Assured Service (AS) provides some minimal level of QoS guarantee by treating more preferably than traditional Best Effort (BE) traffic and by using different level of drop probabilities within the same AS classes. In this paper, we investigate the ECN's capability of improving overall goodput of the flows and the possibility of resolving the fairness problem among the flows belonging to same class in Differentiated Services architecture.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8B
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• pp.689-698
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• 2008

The performance of a TCP protocol on MANETs has been studied in a numerous researches. One of the significant reasons of TCP performance degradation on MANETs is inability to distinguish between packet losses due to congestion from those caused by nodes mobility and as consequence broken routes. This paper presents the Cluster-Label-based Routing (CLR) protocol that is an attempt to compensate source of TCP problems on MANETs - multi-hop mobile environment. By utilizing Cluster-Label-based mechanism for Backbone, the CLR is able to concentrate on detection and compensation of movement of a destination node. The proposed protocol provides better goodput and delay performance than standardized protocols especially in cases of large network size and/or high mobility rate.

• Electronics and Telecommunications Trends
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• v.14 no.4 s.58
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• pp.10-22
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• 1999

본 고에서는 ATM 교환기에서 비실시간 트래픽를 수용하기 위한 버퍼 관리방법에 대하여 조사하고 분석하였다. ATM 교환기는 고속으로 교환하지만 트래픽이 많을 경우 혼잡이 발생할 수 있으므로 비실시 간 트래픽을 제어하여 사용자가 요구하는 다양한 서비스 품질(Quality of Service: QoS)을 제공해야 한다. TCP는 대표적인 비실시간 트래픽으로서 교환 및 전송중에 패킷 손실이 발생하는 경우 양 종단의 TCP에서 재전송 및 TCP 흐름 제어를 한다. 본 고에서는 ATM 교환기에서 제한된 버퍼를 효율적으로 활용하기 위하여 버퍼 부족현상이 예견되는 경우 패킷 폐기 정책에 따라 패킷을 폐기함으로써 TCP 계층에서의 처리량(goodput)을 증대시키는 방법을 검토하였다. 아울러 다중점대점 연결을 제공하는 가 상채널 병합(VC merging) 기능을 구현하기 위한 ATM 교환기의 버퍼 요구사항과 지연에 대하여 살펴 보았다.

• The KIPS Transactions:PartC
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• v.8C no.3
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• pp.345-350
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• 2001

IP 네트워크 상에 TCP 데이터 트래픽의 제공은 처리율과 공정성을 향상시키기 위해 특별한 기법이 필요하다. 여기에는 DT와 RED와 같은 많은 기법들이 제안되었다. RED 알고리즘은 폭주를 회피하고 적은 지연과 높은 처리율을 유지하기 위한 목적으로 제안되었다. 현재의 TCP/IP 환경에서 TCP 근원지는 Slow-Start 단계에 들어감으로써 드롭된 패킷에 반응하지만, 네트워크 이용률은 급속히 떨어진다. 폭주를 탐지하고, 이를 무작위로 선택된 연결에 통보하므로써 RED는 글로벌 동기화 및 공정성 문제를 유발한다. 본 논문에서는 성능을 향상시키기 위해 공정성을 유지하고, 글로벌 동기화 문제를 해결할 수 있는 능동적인 큐 관리 알고리즘을 제안한다. 제안된 알고리즘은 버퍼크기와 임계치 변화에 따른 goodput, 처리율, 공정성의 평가인자를 이용하여 기존의 기법인 DT, RED와 비교 분석을 수행하고, 제안된 기법의 타당성을 보인다.