• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.495-507
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• 2006

In wireless local area networks (WLANs), the successful design of scheduling algorithm is a key factor in guaranteeing the various quality of service (QoS) requirements for the stringent real-time constraints of multimedia services. In this paper we propose a multipolling-based dynamic scheduling algorithm for providing delay guarantees to multimedia traffics such as MPEG streams. The dynamic algorithm exploits the characteristics of MPEG stream, and uses mini frames for feedback control in order to deliver dynamic parameters for channel requests from stations to the point coordinator (PC) operating at the access point (AP). In this scheme, the duration of channel time allocated to a station during a superframe is changed dynamically depending on the MPEG frame type, traffic load and delay bound of the frame, etc. Performance of the proposed scheme is investigated by simulation. Our results show that compared to conventional scheme, the proposed scheme is very effective and has high performance while guaranteeing the delay bound.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.3B
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• pp.165-173
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• 2012

In this paper, we propose a random backoff scheme for Emergency Warning Messages (EWMs) in the vehicle-to-vehicle environment. The EWMs are disseminated from a vehicle that detects an emergency situation to other vehicles in a multi-hop fashion. Since the vehicle-to-vehicle communication based on IEEE 802.11 adapts CSMA/CA, the density of vehicles increase the probability of collisions between transmissions. Moreover, in the presence of background traffic, the EWM should have a higher priority than that of other messages in neighboring vehicles. To that end, we propose the Distant-Dependent Adaptive Backoff (DDAB) scheme, which set a different contention window for random backoff depending on the distance from the sender to the receiver. In the case when a vehicle is expected to located in the outskirts of the communication boundary, the proposed scheme makes the contention window size small in order to compete the background traffic transmission. Otherwise the contention window is set to a large number to reduce the collision possibility among the EWM transmissions. Via simulations, we show that the proposed scheme performs better than the previous schemes for EWM.

• The Journal of the Korea Contents Association
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• v.8 no.5
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• pp.52-60
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• 2008

A simple Time Division Multiplex(TDM) switching system which has been widely in satellite networks provides any size of bandwidth for a number of low bandwidth subscribers by allocating proper number of time slots in a frame. In this paper, we propose a new approach based on graph coloring model for efficient time slot assignment algorithm in contrast to network flow model in previous works. When the frame length of an initial matrix of time slot requests is 2's power, this matrix is divided into two matrices of time slot requests using binary divide and conquer method based on the graph coloring model. This process is continued until resulting matrices of time slot requests are of length one. While the most efficient algorithm proposed in the literature has time complexity of $O(N^{4.5})$, the time complexity of the proposed algorithm is $O(NLlog_2L)$, where N is the number of input/output links and L is the number of time slot alloted to each link in the frame.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12C
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• pp.1239-1247
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• 2005

It is important to improve TCP performance in Self-similar TCP network where signalling between the same end nodes through bidirectional traffic routes. In wireless link, the traffic limitation pattern occurred in two or more TCP connections is applied into MPEC video control as multi time-interval congestion control. For TCP update variable, we extend TCP and perform as function call, and we study a method of relating TCP with LTS module controlling with the information type that is overcoming the limit of feedback loop determined by RTT. For comparison, we measure the TCP throughput without LTS and verify the fairness by means of meta control. The improved TCP performance is shown by that the number of connections of traffic congestion control increases when RTT increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.4A
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• pp.259-270
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• 2005

This paper proposes a mathematical model to analyze call-and packet-level performance of the TD-CDMA/TDD system which could serve a flexible radio resource management against multi-type heterogeneous and asymmetrical traffic conditions. On call-level analysis, the mathematical model based on queueing theory performs multi-dimensional operations using random vectors or matrices to consider multiple types of traffic and also deal with asymmetrical up- and down-direction transmissions separately. Employing the mathematical model, we obtain rail blocking probability for each type of traffic and also the optimum switching-point with the smallest call flocking probability. And on packet-level analysis, employing a non-prioritized queueing scheme between circuit and packet calls, we solve 2-dimensional random vector problem composed of the queue length for packets and the number of circuit calls being served. Finally, packet-level performance is analyzed in terms of the packet loss probability and the buffer size required under mixed-traffic conditions of multiple types of circuit and packet calls.

• The KIPS Transactions:PartC
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• v.10C no.2
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• pp.217-232
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• 2003

QoS routing can improve network performance while providing support for QoS guarantees. These benefits, however, comes with additional routing costs such as more complex and frequent route computation and the protocol overheads to exchange dynamic network state information. Moreover, little has been done to mininize the impact of the QoS traffic to the best effort traffic or to enhance the routine Performance of the best effort traffic when QoS routing is deployed. In this paper, it is proposed that a sewer based routing mechanism, which supports the QoS routing without incurring the QoS routing protocol overhead for the network state update exchanges and enhances the performance of the best effort traffic without affecting the performance of QoS routing. Simulation results show that the proposed scheme enhances the routing performance for the QoS traffic while reducing the routing protocol overhead. The routing performance of the best traffic is also improved with virtually no impact to the routine performance of the QoS traffic. The proposed scheme is shown to be especially effective when the ratio of QoS traffic is high, that is, when the impact of the QoS traffic to the performance of best effort traffic is significant.

• The KIPS Transactions:PartC
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• v.12C no.1 s.97
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• pp.83-96
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• 2005

The multichannel switch is an architecture widely used for ATM (Asynchronous Transfer Mode). It is known that the fault tolerant characteristic can be incorporated into the multichannel crossbar switching fabric. For example, if a link belonging to a multichannel group fails, the remaining links can assume responsibility for some of the traffic on the failed link. On the other hand, if a fault occurs in a switching element, it can lead to erroneous routing and sequencing in the multichannel switch. We investigate several fault localization algorithm in multichannel crossbar ATM switches with a view to early fault recovery. The optimal algorithm gives the best performance in terms of time to localization but it is computationally complex which makes it difficult to implement. We develop an on-line algorithm which is computationally more efficient than the optimal one. We evaluate its performance through simulation. The simulation results show that the Performance of the on-line algorithm is only slightly sub-optimal for both random and bursty traffic. There are cases where the proposed on-line algorithm cannot pinpoint down to a single fault. We enumerate those cases and investigate the causes. Finally, a fault recovery algorithm is described which utilizes the information provided by the fault localization algorithm The fault recovery algorithm providesadditionalrowsandcolumnstoallowcellstodetourthefaultyelement.

• Journal of KIISE
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• v.42 no.8
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• pp.1057-1064
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• 2015

The tactical network is system based on wireless networking technologies that ties together surveillance reconnaissance systems, precision strike systems and command and control systems. Several alternative paths exist in the network because it is connected as a grid to improve its survivability. In addition, the network topology changes frequently as forces and combatants change their network access points while conducting operations. However, most Internet routing standards have been designed for use in stable backbone networks. Therefore, tactical networks may exhibit a deterioration in performance when these standards are implemented. In this paper, we propose Priority based Multi-Path routing with Local Optimization(PMPLO) for a tactical backbone network. The PMPLO separately manages the global and local metrics. The global metric propagates to other routers through the use of a routing protocol, and it is used for a multi-path configuration that is guaranteed to be loop free. The local metric reflects the link utilization that is used to find an alternate path when congestion occurs, and it is managed internally only within each router. It also produces traffic that has a high priority privilege when choosing the optimal path. Finally, we conducted a simulation to verify that the PMPLO can effectively distribute the user traffic among available routers.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.290-291
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• 2000

광전달망에서 전송용량의 폭발적인 수요 증가에 대처하기 위한 최적의 솔루션으로 파장분할다중화(WDM: wavelength division multiplexing) 방식이 도입되고 있으며, 그 적용 영역 또한 장거리 시외망, 단거리 시내망부터 인터넷 트래픽 전달용 백본망을 위한 핵심기술로 정착될 것으로 예측하고 있다. WDM 광전송 방식은 기존의 시분할 다중(TDM: time division multiplexing) 방식이 갖는 동기식(SDH: synchronous digital hierarchy) 전송기술의 한계를 보완할 수 있으며, 신호의 다중화 및 역다중화 구성체계가 단순하고, 입력 광신호에 대한 신호속도나 형태등의 제한도 없기 때문에, 기존의 동기식 전송에 비해 전송용량을 쉽게 확장할 수 있다는 장점을 가지고 있다. (중략)

• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.584-586
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• 1999

본 논문에서는 파장 재사용 이중 단일홉 WDM(Wavelength Division Multiplexing) 통신망에서 전체 노드의 수가 사용 가능한 파장의 수보다 클 경우에 트래픽의 지역성(locality)을 고려하여 시간 분할 다중 접속 (TDMA) 방식으로 파장을 이용하는 다중 접근 알고리즘을 제안한다. 사용 가능한 파장을 그룹내에서 사용하는 전역 파장과 그룹간의 통신에 사용하는 지역 파장으로 나누고 전역 파장은 통신망에 속하는 모든 노드가 공유하고 지역 파장은 그룹내의 노드가 공유한다. 따라서 지역 파장은 모든 그룹 내에서 재사용 가능하기 때문에 전체 파장의 사용율이 증가한다. 모든 노드는 전역파장와 지역 파장으로 동조 가능한 하나의 동조 송신기와 전역 파장 중에 하나의 파장으로 수신 파장이 고정된 고정 수신기와 지역 파장 중에 하나의 파장으로 수신 파장이 고정된 고정 수신기를 가진다. 제안하는 알고리즘은 노드에서 패킷의 전송 요구가 필요한 만큼 슬롯 시간을 할당받아 모든 패킷을 연속해서 전송하는 슬롯 예약 방식을 채택한다. 이 방식은 동조 시간을 최소화함으로써 슬롯 시간을 모드 노드가 균일하게 할당하여 전체 동조 시간이 길어지는 고정 할당 방식보다 파장 사용율이 효율적이다.