• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.6
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• pp.81-86
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• 2011

In one of the most impacting schemes proposed to address the TCP throughput problem over network coding, the network coding layer sends an acknowledgement if an innovative linear combination is received, even when a new packet is not decoded. Although this scheme is very effective, its implementation requires a limit on the coding window size. This limitation causes low TCP throughput in the presence of packet reordering. We argue that a TCP variant detecting a packet loss relying only on timers is effective in dealing with the packet reordering problem in network coding environments as well. Also we propose a new network coding layer to support such a TCP variant. Simulation results for a 2-path environment show that our proposed scheme improves TCP throughput by 19%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2B
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• pp.130-142
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• 2009

In this paper, we propose a self-adaptation framework that selects a TCP variant adapted to current end-to-end path among available TCP variants. There is no single version of TCP that is suitable to all network environments since the causes for performance degradation are different one another according to characteristics of network environments. Thus, determining that which TCP variants should be selected in order to get best performance is very important. To enable adaptation through such determination, we integrate the existing network estimation schemes and some TCP variants into our framework then make light-weight performance knowledge database for TCP selection. Through implementing and evaluating the proposed framework we show that our solution can help TCP get high and stable performance on the various types of network environments by pure end-to-end.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.1
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• pp.139-145
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• 2016

Dumbbell is the most basic topology that can be used in almost all kind of network experiment within it or just by little expansion. While Transmission Control Protocol TCP is the basic protocol that is used for the connectivity among networks and stations. TCP major and basic goal is to provide path and services to different applications for communication. For that reason TCP has to transfer a lot of data through a communication medium that cause serious congestion problem. To calculate the congestion problem, different kind of pre-cure solutions are developer which are Loss Based Variant and Delay Based Variant. While LBV keep track of the data that is going to be passed through TCP protocol, if the data packets start dropping that means congestion occurrence which notify as a symptom, TCP CUBIC use LBV for notifying the loss. Similarly the DBV work with the acknowledgment procedure that is used in when data ACK get late with respect to its set data rate time, TCP COMPOUND/VAGAS are examples of DBV. Many algorithms have been purposed to control the congestion in different TCP variants but the loss of data packets did not completely controlled. In this paper, the congestion control algorithms are implemented and corresponding results are analyzed in Dumbbell topology, it is typically used to analyze the TCP traffic flows. Fairness of throughput is evaluated for different TCP variants using network simulator (NS-2).

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.1
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• pp.7-13
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• 2011

While the TCP throughput degradation problem in coded wireless mesh networks is well-known, few effective solutions have been proposed. Most schemes proposed attempts to mask packet reordering by ordering packets at a lower layer or to adjust a packet transmission rate to solve the scarcity problem of coding opportunities. Through the throughput comparison of traditional standard TCP variants, we show that losses and duplication of TCP acknowledgements in coded wireless mesh networks can impact throughput. In addition, we show that a TCP variant that does not rely on duplicate acknowledgements is more suitable for coded wireless mesh networks.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.484-486
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• 2002

Mobile IP는 이동단말의 macro-mobility를 지원하는 표준이다. 그런데, Mobile IP는 도메 인내에서의 빈번한 핸드오프상에서는 많은 단점이 있다. HA(Home Agent)로 빈번하게 시그널을 보내기 때문에 많은 제어 메시지 오버gp드가 있으며, 핸드오프중의 많은 패킷 손실이 있다. Micro-mobility프로토콜은 기존 mobile IP의 단점을 보완하기 위해 나온 프로토콜이다. 무선 네트웍상의 도메인내에서의 이동성을 지원하며, 손실과 메시지 오버 헤드를 줄여 핸드오프시 높은 성능향상을 주고, 효율적인 위치관리를 제공한다. TCP(Transmission Control Protocol)는 전통적인 네트웍에서 잘 동작하는 신뢰성 있는 연결지향성 전송프로토콜이다. 그러나, TCP는 Mobile IP를 이용한 무선환경하에서는 잦은 핸드오프 때문에 손실과 지연이 일어나서 많은 성능저하가 일어난다. 본 논문에서는 TCP Tahoe, Reno, NewReno, SACK를 micro-mobility 프로토콜상에서 사용하였을 때 어느 TCP버전과 micro-mobility프로토콜이 가장 효율적인지를 제시한다.

• Journal of Communications and Networks
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• v.8 no.3
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• pp.351-359
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• 2006

In this article, we present a new slow-start variant, which improves the throughput of transmission control protocol (TCP) Vegas. We call this new mechanism Gallop-Vegas because it quickly ramps up to the available bandwidth and reduces the burstiness during the slow-start phase. TCP is known to send bursts of packets during its slow-start phase due to the fast window increase and the ACK-clock based transmission. This phenomenon causes TCP Vegas to change from slow-start phase to congestion-avoidance phase too early in the large bandwidth-delay product (BDP) links. Therefore, in Gallop-Vegas, we increase the congestion window size with a rate between exponential growth and linear growth during slow-start phase. Our analysis, simulation results, and measurements on the Internet show that Gallop-Vegas significantly improves the performance of a connection, especially during the slow-start phase. Furthermore, it is implementation feasible because only sending part needs to be modified.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.58-65
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• 2016

Satellite communication is a wide area network (WAN) which provides communication service worldwide. However, the performance of TCP can be seriously degraded in the satellite networks due to limited bandwidth, long round-trip time (RTT) and high bit error rate (BER) over satellite links. In order to improve the performance of TCP, this paper proposes cross-layer Performance Enhancing Proxy (PEP) in digital video broadcasting-return channel via satellite (DVB-RCS) networks. The proposed protocol sets TCP Congestion Window (CWND) size by using satellite resource allocation information exchanged between TCP and the link-layer. we implement PEP testbed based on Linux to evaluate the performance of the proposed protocol. The simulation results show that the proposed protocol performs better than standard TCP both in single and multiple sessions in variant BER, because the proposed protocol sets TCP CWND size by using satellite resource allocation.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.8
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• pp.778-782
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• 2008

The performance in combination of wired and wireless mesh network which will be a main access network in future internet is directly linked with service quality to users. In this paper, we evaluate variant TCP performance and analyze traffic characteristics on Wireless (Seoul National University Mesh testbed) - Wired (KOREN/Abilene) - Wireless (HP Mesh testbed in the USA) Network. We found that RTT is proper in this network to serve a VoIP service. Also we propose an enhanced TCP protocol which can perform well in both wireless network which has many packet losses and wired network which has high bandwidth and long delay.

• Journal of KIISE:Information Networking
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• v.29 no.4
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• pp.358-367
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• 2002

The IETF Differentiated Services (Diffserv) WG focused on Providing service differentiation on the Internet. One problem of the Diffserv Assured Services (AS) architecture is that it cannot guarantee fairness and throughput assurance. In this paper, we propose two schemes for guaranteeing fairness among the various target rates in the AS architecture. One is a variant of RED with IN and OUT (RIO), called the improved RIO (IRIO). The other is a variant of Time Sliding Window (TSW), called the improved TSW (ITSW). To validate the Proposed schemes, their behaviors are then examined under various simulation environments. The simulation results showed that IRIO and ITSW improved fairness and the throughput assurance in the AS architecture.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1732-1737
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• 2004

This paper proposes Internet-based checking technique for machine-tools with variant CNC (Computerized Numerical Controller). According to the architecture of CNC, CNC is classified into two types such as CAC (Closed Architecture Controller) which is conventional CNC, and OAC (Open Architecture Controller) which is a recently introduced PC-based controller. CAC has a closed architecture and it is dependent on CNC vender specification. Because of this, it has been very difficult for users to implement an application programs in CNC domain. Therefore, an additionally special module is required for Internet-based application such as remote checking. In this case, web I/O embedded module can be efficiently applied for Internet-based checking. The module is directly attached to TCP/IP network for communication. In order to obtain the monitoring data of CNC machines, the I/O signals of the module are assigned to PLC (Programmable Logic Controller) input and output (I/O) signals within CNC domain. On the other hand, OAC has a PC-based open architecture and an additional module is not necessary for the connection with external site. Because of this, a simple DAU is just used for signal sensing and data acquisition without additional communication modules. For Internet-based remote checking of machine-tools with OAC, a user-defined daemon and application programs are implemented as the form of internal function within the PC-based controller. Internet communication is performed between the daemon program in CNC domain and web script programs in external server. Checking points defined in this research are classified into two categories such as structured point and operational point. The formal includes the vibration of bearing, temperature of spindle unit and another periodical management. And the latter includes oil checking, clamp locking/unlocking and machining on/off status.