• Proceedings of the Korea Information Processing Society Conference
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• 2001.10b
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• pp.1501-1504
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• 2001

MPEG-4 비디오 스트림을 전송하기 위해 RTP 프로토콜을 사용할 경우 RTP 패킷에 MPEG-4 비디오 스트림을 수용하기에 적절한 페이로드 포맷이 정의되어야 한다. RTP 페이로드에 MPEG-4 비디오 스트림을 수용하기 위한 기존의 방법은 MPEG-4 코덱으로부터 생성된 비디오 스트림의 형태에 따라 많은 종류의 페이로드 포맷이 정의되어야 하는 문제점이 있거나, 혹은 각 계층에서 생성된 스트림을 (in 패킷화하는 방법이 명료하지 않은 문제점 등이 있다. 이 논문에서는 MPEG-4 시스템을 사용 하지 않고, MPEG-4 비디오 기초스트림을 RTP 패킷에 담아 전송하기 위한 새로운 RTP 페이로드 포맷을 제안하였고, 제안된 포맷을 이용하여 MPEG-4 비디오를 전송하는 시스템을 설계 및 구현하였다. 제안된 RTP 페이로드 포맷은 비디오 객체(Video Object)에 대한 RTP 페이로드 포맷만을 정의하여 포맷의 종류를 최소화함으로써 포맷의 종류가 많아짐으로해서 생기는 부가적인 오버헤드를 감소시켰으며, 또한 하나의 RTP 패킷에는 단 하나의 비디오 객체에 대한 정보만을 저장하여 비디오 객체간의 독립성을 유지하였다. 제안된 포맷을 이용하여 구현된 MPEG가 비디오 전송시스템은 RTP 패킷의 크기를 pad-MTU와 같거나 작게 설계함으로써, IP 계층에서 RTP패킷의 단편화 현상이 발생하지 않고 효율적인 전송이 이루어지도록 하였다.

• The Transactions of the Korea Information Processing Society
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• v.6 no.4
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• pp.1045-1057
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• 1999

Packet-switched multistage interconnection networks(MINs) have been widely used for digital switching systems and super computers. In this paper we show that multiple packets in a switching element can move to the succeeding switching element in one network cycle by fully utilizing the cycle bandwidth. Only one packet movement was usually assumed in typical MINs. we present an analytical model for the MNs with the multiple packet movement scheme, and validate it by computer simulation. Comparisons with the traditional MINs of single packet movement reveal that the throughput is increased up to about 30% for practical size MINs. Similar result was also obtained for delays. The performance increase is more significant when the network traffic is nonuniform.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.921-924
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• 2007

본 논문에서는 멀티 홉 무선 네트워크에서 적용 가능한 통합적인 MAC 및 라우팅 프로토콜인 ExOR 의 성능개선을 위한 방안을 제시하였다. ExOR 은 무선 네트워크의 전송이 브로드 캐스트 방식으로 이루어지는 것을 이용하여 기회주의적인 라우팅을 시도함으로써 멀티 홉 무선 네트워크에서 링크의 사용량을 낮추고 쓰루풋을 높일 수 있는 전송 기법이다. 하지만 ExOR 은 멀티 홉 무선 네트워크의 크기가 확장되거나 링크의 전송률이 낮다면 라우팅에 참여하는 노드들의 패킷 전달이 원활하지 않기 때문에 지연시간이 크게 증가하여 성능이 급격히 저하되는 단점이 있다. 본 논문에서는 ExOR 라우팅 프로토콜을 적용 시, 패킷을 전달하는 노드 이외의 다른 노드들이 자기 차례가 되기 전까지 아무 일도 하지 않는다는 점에 착안하여 동시에 2 개 이상의 노드가 패킷을 전달하는 방식을 제안하였다. 본 논문에서는 ExOR 라우팅에 참여하는 노드가 패킷을 전달 할 때, 패킷 간 충돌 및 간섭을 최소로 할 수 있는 2 개 이상의 다른 노드를 선택하여 동시에 패킷 전송을 시도하는 방식으로 지연시간을 줄이고, 쓰루풋을 향상시키는 것을 시뮬레이션을 통하여 확인하였다.

• Journal of Digital Contents Society
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• v.9 no.1
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• pp.61-67
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• 2008

In this paper, MAC algorithm for the IEEE 802.11 DCF improving the performance is proposed and analyzed by simulation. The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF(Distributed Coordination Function) and PCF(Point Coordination Function). The DCF controls the transmission based on CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance), that decides a random backoff time with the range of CW(Contention Window) for each station. Normally, each station increase the CW to double after collision, and reduces the CW to the minimum after successful transmission. The DCF shows excellent performance relatively in situation that competition station is less but has a problem that performance is fallen from throughput and delay viewpoint in situation that competition station is increased. This paper proposes an enhanced DCF algorithm that increases the CW to maximal CW after collision and decreases the CW smoothly after successful transmission in order to reduce the collision probability by utilizing the current status information of WLAN. To prove efficiency of proposed algorithm, a lots of simulations are conducted and analyzed.

• Journal of Internet Computing and Services
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• v.6 no.3
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• pp.85-95
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• 2005

Whereas the traditional multicast schemes based on Mobile IP can support a limited number of very large multicast groups, the Xcast protocol can support a very large number of small multicast groups, In the Xcast, the source node encodes the list of destinations in the Xcast header. Therefore, the maximum packet size in the network limits the number of destinations that a Xcast packet may have. In this paper, an enhanced Xcast protocol is proposed to solve the multicast group size limitation of the existing Xcast protocol in providing multicast service for mobile nodes. Moreover, the SIP (a very flexible control plane protocol) is integrated with the proposed multicast scheme to provide mobility awareness on the application layer. The simulation results verify that the proposed multicast scheme not only increases the packet delivery ratio and the data packet forwarding efficiency but also achieves low latency of packets in the network.

• The KIPS Transactions:PartC
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• v.9C no.6
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• pp.847-856
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• 2002

Cellular network applications are growing drastically and this requires a fast and efficient transport method between the base station and the mobile switching center. One possible solution is to use ATM links. The low data rate and small-sized packets in the typical cellular applications imply that significant amount of link bandwidth would be wasted, if this small sized packet is carried by one ATM cell. For efficient operation for such cellular and low bit rate applications, a new type of ATM Adaptation Layer, AAL Type 2, has been proposed. In this paper, the principles of AAL Type 2 are briefly described along with the introduction of other alternatives which have formed the basis for this new AAL. The result from the simulation to study the performance of the AAL Type 2 is discussed from the view point of packet delay and ATM cell use efficiency. Due to the variable size of packets in this application, the fairness issue in serving variable sized packets is also discussed along with the effect of fair queueing algorithm implemented at AAL Type 2.

• The Transactions of the Korea Information Processing Society
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• v.7 no.11S
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• pp.3684-3693
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• 2000

In this paper, performance of a nonblocking high speed packet switch with switching capacity m which adopts a dynamic priority control function (DPCF) of a threshold- based Bernoulli priority jump (TBPJ) scheme is considered. Each input queue has two separate buffers with different sizes for two classes of traffics, delay-sensitive and loss-sensitive traffics, and adopts a TBPJ scheme that is a general state-dependent Bernoulli scheduling scheme. Under the TBP] scheme, a head packet of the delay-sensitive traffic buffer goes into the loss -sensitive traffic buffer with Hernoulli probability p according to systems states that represent the buffer thresholds and the number of packets waiting for scheduling. Performance analysis shows that TBPJ scheme obtains large performance build-up for the delay-sensitive traffic without performance degradation for the loss-sensitive traffic. In addition to, TBP] scheme shows better performance than that of HOL scheme.

• Journal of Korea Multimedia Society
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• v.8 no.1
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• pp.71-78
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• 2005

When a PDA is used as a mobile terminal in an infrastructure network based on 802.11b standard wireless LAN, we measured and evaluated the performance of multimedia data transmission. In general, PDAs are mainly used tot receiving bulk data like multimedia data. However, while a PDA as a mobile host transfers multimedia data to a desktop PC as a fixed host in such a network, the time taken to receive data from the PC to the PDA is always longer than the time taken to send data from the PDA to the PC by at least 53%. Thus, we consider some critical factors that affect the time taken to receive Our experimental results show that with the PDA the time taken to access a file for writing is longer than the time taken to access a file for reading of to 4.11 times. In addition, a dramatic change of the site of the receiver window, from 686 bytes to 32,383 bytes, prolongs the time taken to receive. To transfer data without any inter-packet interval for the PDA and to increase the size of the TCP receive buffer will be effective in improving the delay to receive data.

• 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.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.9
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• pp.1941-1946
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• 2009

Wireless sensor networks do the monitoring and collecting information in the environment instead of human. Sensor networks are consisted of small sensor nodes with very limited hardware resource and very low network bandwidth. The wireless communication environment causes lots of communication errors so that the sensor network requires error correction technique to increase the reliability of network. The performance of error correction technique could be increased by the researches about the error pattern of CRC. In the paper, we did the performance evaluation - transmission interval, distance between sensor nodes, racket size, and RF power - that affects to the success ratio of data transmission in the indoor environment. we propose the performance metrics of system configuration based on the analysis of performance evaluation.