• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.2
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• pp.304-309
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• 2004

Recently, the needs for multimedia stream such as digital audio and video in the Internet has increased tremendously. Unlike TCP, the UDP protocol, which has been used to transmit streaming traffic thorough the Internet, does not apply any congestion control mechanism to regulate the data flow thorough the shared network And it leads to congestion collapse of the Internet and results in long-term transmission delay. To avoid any adverse effect on the current Internet functionality, a now protocol of modification or addition of some functionality to perform congestion control and to reduce huge transmission delay in transmitting of multimedia stream are in study. TCP-friendly congestion control mechanism is classified into two : one is window-based congestion control scheme using general window management functionalities, the other is rate-based congestion control scheme using TCP modeling equation. In this paper, we propose an algorithm for improving the transmitting rate on a hybrid TCP-friendly congestion control scheme combined with widow-based and late-based congestion control for multimedia stream. And we also simulate the performance of improved TEAR implementation using NS. With He simulation results, we show that the improved TEAR can provide better fairness and lower rate fluctuations than TCP.

• Journal of Korean Society of Transportation
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• v.27 no.5
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• pp.7-16
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• 2009

This paper proposes a plan which can raise the accuracy of economic benefit estimation in road construction projects. The point of existing economic appraisals may be that the speeds forecasted by models are different from the field speeds because only volumes are calibrated in the road network. The result of such a calibration has an influence on estimating wrong economic benefits in terms of vehicle operating cost savings, travel time savings, and air pollution savings. Then this study performs a calibration when volumes are at the same amount but the calibration between the field speeds and model speeds is different from each other with two different volume-delay functions; the differences of benefits are confirmed according to two different speed calibrations. Three improvement schemes, including the development of a new volume-delay function, are proposed in this study in order to solve the problem of current benefit calculations. The outcome of this study will help practitioners perform more accurate benefit calculations and reasonable economic appraisals.

• Journal of Korea Multimedia Society
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• v.11 no.7
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• pp.966-976
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• 2008

Providing Quality-of-Service(QoS) guarantee requires the reservation of resource needed to accommodate the traffic flow of service for which resource reservation protocol(RSVP) was introduced. However, if any RSVP-capable router on the path fails to accommodate the traffic flow due to lack of resource, the flow is not allowed no matter how much surplus resources other routers on the path have. In order to solve this problem, this paper proposes a resource reservation method that can adjust adaptively the delay budget of traffic flow allocated to each RSVP-capable router in which the router uses the recently developed general-time fair queuing scheduler. The results of the simulation applying the proposed method to an evaluation network show that it may yield the gain of up to 90% compared to that in the original one in terms of the number of admitted flows.

• The Journal of the Convergence on Culture Technology
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• v.10 no.4
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• pp.589-594
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• 2024

In this paper, we introduce the results of the Sounding Rocket LTE communication test using the LTE-Cat.M1 module. The developed LTE data transmission/reception system consists of Mission-Mounted Equipment(Payload) and Ground Observation Equipment(GOE), and the delay rate was secured based on the time between data measured when received from the GOE by constantly transmitting data from the Payload at a speed of 10 Hz. In order to increase the accuracy of the actual flight test, ground network delay rate tests, hardware internal delay rate tests, and ground tests were performed. As a result of the flight test, it was confirmed that the handover failed in the upward phase and the communication was lost for 13 seconds, and then the parachute was deployed and the communication was reconnected in a situation with a constant positional displacement. LTE-Cat.M1 technology is expected to be utilized for descent phase observation missions or data backup during Sounding Rocket missions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.2C
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• pp.160-169
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• 2002

An ATM-PON (Passive Optical Network) system consists of an OLT (Optical Line Termination), multiple ONUs (Optical Network Units) and the optical fiber which has a PON (Passive Optical Network)configuration with a passive optical splitter. To avoid cell collisions on the upstream transmission, an elaborate procedure called as ranging is needed when a new ONU is installed. The ONU can send upstream cells according to the grant provided by the OLT after the procedure. To prevent collisions being generated by the variation of several factors, OLT must performs continuously the cell phase monitoring. It means that the OLT predicts the expected arrival time, monitors the actual arrival time for all upstream cells and calculates the error between the times. Accordingly, TC (Transmission Convergence) chip in the OLT needs a predictor which predicts the time that the cell will arrive for the current grant. In this paper, we implement the predictor by using shift registers of which the length is equivalent to the equalized round trip delay. As each register consists of 8 bit, OLT can identify which ONU sends what type of cell (ranging cell, user cell, idle cell, and mini-slot). Also, TC chip is designed to calculate the effective bandwidth for all ONUs by using the function of predictor. With the time simulation and the measurement of an implemented optical board, we verify the operation of the predictor.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.149-158
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• 2006

We proposed a method for improving a performance of TCP downstream between a desktop PC as a fixed host and a PDA as a mobile host in a wired and wireless network based on IEEE 802.11x wireless LAN. With data transmission between these heterogeneous terminals a receiving time during downstream is slower than that during upstream by 20% at maximum. The reason is that their congestion window size will be oscillated due to a significantly lower packet processing rate at receiver compared to a packet sending rate at sender. Thus it will cause to increase the number of control packets to negotiate their window size. To mitigate these allergies, we proposed two distinct methods. First, by increasing a buffer size of a PDA at application layer an internal processing speed of a socket receive buffer of TCP becomes faster and then the window size is more stable. However, a file access time in a PDA is kept nearly constant as the buffer size increases. With the buffer size of 32,768bytes the receiving time is faster by 32% than with that of 512bytes. Second, a delay between packets to be transmitted at sender should be given. With an inter-packet delay of 5ms at sender a resulting receiving time is faster by 7% than without such a delay.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.8
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• pp.1735-1742
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• 2011

Now a days, as a mass-storage USB becomes comfortable to carry, function of USB is being developed fast. However, there is a problem that the personal information which is stored in USB could be exposed being used with negative purpose without other certification process. This paper suggests OTP(One-Time Password)-based certification protocol of USB to securely protect personal information stored in USB without additional certification information. The proposed OTP based certification protocol of USB not only demands low calculations but also prevents physical approach of USB of other network and does not allow unnecessary service access of user because it conducts simple action and uses one-way hash function. Therefore, communication overhead and service delay is improved. In the experiment, the proposed protocol compares and evaluates throughput of certification server according to the numbers of USB and delay time of packet certification with a device(USB driver) which simply save device and a device(USB Token) which can calculate by oneself. As a result, it is improved as the number of 12.5% in the certification delay time on average and is improved as the number of 10.8% in the throughput of certification server according to the numbers of USB.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.1
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• pp.1-21
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• 2013

The release of IEEE 802.15.4e specification significantly develops IEEE 802.15.4. The most inspiring improvement is the enhancement for medium access control (MAC) sublayer. To study the performance of IEEE 802.15.4e MAC, in this paper we first present an overview of IEEE 802.15.4e and introduce three MAC mechanisms in IEEE 802.15.4e. And the major concern here is the Time Slotted Channel Hopping (TSCH) mode that provides deterministic access and increases network capacity. Then a detailed analytical Markov chain model for TSCH carrier sense multiple access with collision avoidance (CSMA-CA) is presented. Expressions which cover most of the crucial issues in performance analysis such as the packet loss rate, energy consumption, normalized throughput, and average access delay are presented. Finally the performance evaluation for the TSCH mode is given and we make a comprehensive comparison with unslotted CSMA-CA in non-beacon enabled mode of IEEE 802.15.4. It can validate IEEE 802.15.4e network can provide low energy consumption, deterministic access and increase network capacity.

• Journal of Advanced Navigation Technology
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• v.14 no.4
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• pp.537-544
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• 2010

The PMIPv6 is a network controlled mobility management protocol in which mobile nodes never participate in IP mobility protocol signaling. One issue in using PMIPv6 for multicast service is that a new component should be added as the mobility management functions are located not on the device but on the network. Currently, standardization activities for providing muticast services with PMIPv6 have been actively in progress. This paper addresses some issues about the on-going standardization works for providing efficient real-time multicast services with PMIPv6, and proposes a scheme for minimizing hand over delays and packet losses by using a new neighbor cell reporting method. The proposed scheme has been verified to outperform the existing scheme in hand over delay and packet loss perfonnrmces by using computer simulations.

• The KIPS Transactions:PartC
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• v.16C no.4
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• pp.477-486
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• 2009

This paper proposes a dynamic bandwidth allocation (DBA) algorithm with adaptive maximum transmission window (DBA-AMTW) to increase channel utilization in Ethernet passive optical networks (EPONs). A polling mechanism in EPON determines channel utilization and puts constraints on DBA algorithm and scheduling. DBA algorithms based on interleaved polling with stop (IPS) allocate transmission windows to optical network units (ONU) considering requests of all ONUs. However channel idle time when any ONU does not transmit packets decreases channel utilization. Proposed DBA-AMTW improves efficiency of a network and allocates transmission windows effectively by appropriate DBA computation from REPORT messages of all ONUs. An adaptive maximum transmission window for each ONU determined by a DBA computation in the previous scheduling cycle. Simulation results show that the proposed DBA algorithm improves performance of throughput and average delay time.