• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.11B
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• pp.1016-1022
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• 2003

The EPON has been actively studied as one of the access networks for the economic configuration of FTTH. The EPON must support the dynamic bandwidth allocation to the subscribers in order to support the QoS due to its base on Ethernet technology EFM SG, which is actively working for the standardization of EPON, also recently decided to select DBA. Therefore in this paper, we designed a ONU buffer scheduling algorithm(AIWFQ) and a scheme of DBA(Class-based FCFS) for the OLT suitable for embodying MPCP of the EPON. In this paper, we proposed methods that the EPON system can make use of by measuring end to end process delay time and the buffer size in order to implement the algorithm by using the OPNET.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2B
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• pp.272-278
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• 2004

The EPON has been actively studied as one of the access networks for the economic configuration of FTTH. The EPON must support the dynamic bandwidth allocation to the subscribers in order to support the QoS due to its base on Ethernet technology. EFM SG, which is actively working for the standardization of EPON, also recently decided to select DBA. Therefore in this paper, we designed a ONU buffer scheduling algorithm (AIWFQ) and a scheme of DBA(Class-based FCFS) for the OLT suitable for embodying MPCP of the EPON. In this paper, we proposed methods that the EPON system can make use of by measuring end to end process delay time and the buffer size in order to implement the algorithm by using the OPNET.

• Journal of information and communication convergence engineering
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• v.4 no.2
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• pp.71-74
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• 2006

A basic access method about IEEE 802.11 MAC layer protocol using IEEE 802.11 wireless LANs is the DCF thatis based on the CSMA/CA. But, cause of IEEE 802.11 MAC layer uses original backoff algorithm (exponential backoff method), when collision occurred, the size of contention windows increases the double size Also, a time of packet transmission delay increases and efficienty is decreased by original backoff scheme. In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs a proposed enhanced backoff algorithm. It is considered the transmission time of transmission control protocol (TCP) packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (A WGN) and Rician fading channel. From the results, a proposed enhanced backoff algorithm produces a better performance improvement than an original backoff in wireless LAN environment. Also, in OFDM/quadrature phase shift keying channel (QPSK), we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and based on the data collected, we can infer the correlation between packet size and the transmission time, allowing for an inference of the optimal packet size in the TCP layer.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.530-533
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• 2006

Recently, a basic access method about IEEE 802.11 MAC layer protocol using IEEE 802.11 wireless LANs is the DCF thatis based on the CSMA/CA. But, cause of IEEE 802.11 MAC layer uses original backoff algorithm (exponential backoff method), when collision occurred, the size of contention windows increases the double size. Also, a time of packet transmission delay increases and efficiency is decreased by original backoff scheme. In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs a proposed enhanced backoff algorithm. It is considered the transmission time of transmission control protocol (TCP) packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (AWGN) and Rician fading channel. From the results, a proposed enhanced backoff algorithm produces a better performance improvement than an original backoff in wireless LAN environment. Also, in OFDM/quadrature phase shift keying channel (QPSK), we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and based on the data collected, we can infer the correlation between packet size and the transmission time, allowing for an inference of the optimal packet size in the TCP layer.

• The KIPS Transactions:PartC
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• v.14C no.4
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• pp.349-358
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• 2007

Ethernet Passive Optical Network(EPON), which is one of PON technologies for realizing FTTx(Fiber-To-The-Curb/Home/Office), can cost-effectively construct optical access networks. In addition, EPON can provide high transmission rate up to 10Gbps and it is compatible with existing customer devices equipped with Ethernet card. To effectively control frame transmission from ONUs to OLT EPON can use Multi-Point Control Protocol(MPCP) with additional control functions in addition to Media Access Control(MAC) protocol function. For EPON, many researches on intra- and inter-ONU scheduling algorithms have been performed. Among the inter-ONU scheduling algorithms, IPS(Interleaved Polling with Stop) based on polling scheme is efficient because OLT assigns available time portion to each ONU given the request information from all ONUs. Since the IPS needs an idle time period on uplink between two consecutive frame transmission periods, it wastes time without frame transmissions. In this paper, we propose a dynamic bandwidth allocation algorithm to increase the channel utilization on uplink and evaluate its performance using simulations. The simulation results show that the proposed Two-phase Cycle Danamic Bandwidth Allocation(TCDBA) algorithm improves the throughput about 15%, compared with the IPS and Fast Gate Dynamic Bandwidth Allocation(FGDBA). Also, the average transmission time of the proposed algorithm is lower than those of other schemes.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.7
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• pp.653-660
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• 2013

This paper deals with the problem of unfairness among uplink TCP (Transmission Control Protocol) flows associated with frame aggregation employed in IEEE 802.11n WLANs (Wireless Local Area Networks). When multiple stations have uplink TCP flows and transmit TCP data packets to an AP (Access Point), the AP has to compete for channel access with stations for the transmission of TCP ACK (acknowledgement) packets to the stations. Due to this contention-based channel access, TCP ACKs tend to be accumulated in the AP's downlink buffer. We show that the frame aggregation in the MAC (Medium Access Control) layer increases TCP ACK losses in the AP and leads to the serious unfair operation of TCP congestion control. To resolve this problem, we propose the TAC (TCP ACK Compression) mechanism operating at the top of the AP's interface queue. By exploiting the properties of cumulative TCP ACK and frame aggregation, TAC serves only the representative TCP ACK without serving redundant TCP ACKs. Therefore, TAC reduces queue occupancy and prevents ACK losses due to buffer overflow, which significantly contributes to fairness among uplink TCP flows. Also, TAC enhances the channel efficiency by not transmitting unnecessary TCP ACKs. The simulation results show that TAC tightly assures fairness under various network conditions while increasing the aggregate throughput, compared to the existing schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.10
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• pp.5098-5115
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• 2017

A number of automotive electronics-safety, driver assistance, and infotainment devices-have been deployed in recent vehicles. This raises new challenges regarding in-vehicular network arbitration. A performance analysis of non-destructive arbitration has revealed a fairness issue. The arbitration prioritizes without collisions, despite multiple simultaneous transmissions; however, the performances of the highest priority node and the lowest priority node are very different. In this paper, an ID-rotation arbitration method to solve the arbitration-fairness problem is proposed. The proposed algorithm was applied to several engine control units (ECUs), including a controller area network (CAN) controller. Experimental results showed that the algorithm improved the fairness as well as the total throughput within a specific performance constraint.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.336-339
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• 2011

In the RTLS(Real Time Location Based System), in case of existing a number of moving target, extremely complecated data flow is can be occurred. In the network where single gateway exists, various data which was collected from sensor node is transmitted along the simple route as time goes by. In case of multi-gateway configuration, the collected data is transmitted through diverse routes rather than simple route. This kind of data causes jams on nodes and this brings down the performance of the network. Different from existing studies, in this thesis, MAC (Media Access Control) protocol which minimizes data collision between nodes and guarantees QoS(Quality of Service) is suggested, in order to communicate efficiently in multi-gateway underwater sensor network environment. In the suggested protocol, source node which wants to transmit data makes a channel reservation to a number of destination node using a RTS packet. Source node reserves a channel without collision, by scheduling CTS response time using expected delay information from neighbor nodes. Once the reservation is made, source node transmit data packet without collision. This protocol analyzes/estimates the performance compared to a method provided from existing studies via simulation. As a results of the analysis, it was comfirmed that the suggested method has better performance, such as efficiency and delay.

• Journal of Broadcast Engineering
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• v.20 no.2
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• pp.300-309
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• 2015

In IEEE 802.11n WLANs(Wireless Local Area Networks), to support high throughput, MAC(Media Access Control) layer adopts A-MSDU(Aggregate-MAC Service Data Unit) and A-MPDU(Aggregate-MAC Protocol Data Unit). Generally, as the A-MPDU uses a selective retransmission capability, A-MPDU provides higher throughput than A-MSDU. However, although A-MPDU uses the selective re-transmission capability, if the size of MPDU within A-MPDU is smaller than the size of minimum MPDU starting spacing, A-MPDU can reduce throughput because of the overhead of retransmission owing to the addition of delimiter, that is a dummy MPDU. Therefore, to overcome the above problem, two-level Aggregation method, where the small MPDU within A-MPDU is replaced by not delimiter but A-MSDU, has been introduced. In the two-level Aggregation method, the existing re-transmission scheme retransmits only A-MPDU, but if the size of retransmission data is smaller than the size of the minimum MPDU starting spacing, the proposed retransmission scheme retransmits the aggregated retransmission data and MSDUs. Therefore, we know that the proposed retransmission scheme have better throughput that the existing retransmission scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.4
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• pp.1076-1089
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• 2012

Home automation networks are good environments for merging sensor networks and consumer electronics technologies. It is very important to reduce the energy consumption of each sensor node because sensor nodes operate with limited power based on a battery that cannot be easily replaced. One of the primary mechanisms for achieving low energy operation in energy-constrained wireless sensor networks is the duty-cycle operation, but this operation has several problems. For example, unnecessary energy consumption occurs during synchronization between transmission schedules and sleep schedules. In addition, a low duty-cycle usually causes more performance degradation, if the network becomes congested. Therefore, an appropriate control scheme is required to solve these problems. In this paper, we propose UDC (Unsynchronized Duty-cycle Control), which prevents energy waste caused by unnecessary preamble transmission and avoids congestion using duty-cycle adjustment. In addition, the scheme adjusts the starting point of the duty-cycle in order to reduce sleep delay. Our simulation results show that UDC improves the reliability and energy efficiency while reducing the end-to-end delay of the unsynchronized duty-cycled MAC (Media Access Control) protocol in sensor-based home automation networks.