• Journal of the Korea Computer Industry Society
• /
• v.2 no.9
• /
• pp.1163-1174
• /
• 2001

A general goal of the ATM(Asynchronous Transfer Mode) network is to support connections across various networks. ABR service using EPRCA(Enhanced Proportional Rate Control Algorithm) switch controls traffics in ATM network. EPRCA switch, traffic control method uses variation of the ACR(Allowed Cell Rate) to enhance the utilization of the link bandwidth. However, in ABR(Available Bit Rate) service, different treatments are offered according to different RTTs(Round Trip Times) of connections. To improve the above unfairness, this paper presents ABR DELAY mechanism, in which three reference parameters for cell delay are defined, and reflect on the messages of RM(Resource Management) cells. To evaluate our mechanism, we compare the fairness among TCP connections between ABR DELAY mechanism and ABR RRM mechanism. And also we execute simulations on a simple ATM network model where six TCP connections and a background traffic with different RTTs share the bandwidth of a bottleneck link. The simulation results, based on TCP goodput and efficiency, clearly show that ABR DELAY mechanism improves the fairness among TCP connections.

• Journal of Korea Multimedia Society
• /
• v.13 no.1
• /
• pp.102-110
• /
• 2010

H.264 SVC(Scalable Video Coding) provides the advantages of low disk storage requirement and high scalability. However, a streaming server or a user terminal has to extract a bit stream from SVC file. This paper proposes a bit stream extraction method which can get the maximum PSNR value while date bit rate does not exceed the available network bandwidth. To do this, this paper obtains the information about extraction points which can get the maximum PSNR value offline and decides the spatial/temporal resolution of a bit stream at run-time. This resolution information along with available network bandwidth is used as the parameters to a bit stream extractor. Through experiment with JSVM reference software, we proved that proposed bit stream extraction method can get a higher PSNR value.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37B no.12
• /
• pp.1174-1185
• /
• 2012

This paper proposes a call admission control scheme for delay guarantee in the wireless mesh networks. The admission of a new call is determined based on the expected delay inferred from the class level available bandwidth at nodes on the path. All nodes under the effects of the new call are considered in designing the call admission control scheme to maintain the delay guarantee of the pre-existing traffic. An effective technique for estimating the available bandwidth of the neighbor nodes is proposed with no addition of message interchanges. The class-level delay control is mainly performed by the queueing discipline while keeping the MAC operation simple. Simulations are performed to show the validity of the proposals. We observe acceptable performances in delay expectation with the addition of new calls. We also show that the proposed call admission control is helpful in guaranteeing the delay performances.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.2B
• /
• pp.124-132
• /
• 2007

Where a wireless LAN and a cellular network coexist, a mobile node has to experience vertical handoffs to move between them. Immediately after the vertical handoffs, TCP must need adaptation latency to adjust its congestion window to the proper size at a newly arrived network to use full of a new end-to-end available bandwidth. Even though SACK TCP has the best performance among other regular TCPs in the previous studies, it still cannot use full of the new available bandwidth quickly due to its inefficient increasing way of congestion window. BIC TCP, that becomes a popular TCP in long fat networks, has great feature working well against vertical handoffs by increasing congestion window exponentially with TCP connection sustained. In this paper, we derive adaptation latency of SACK TCP and BIC TCP numerically, and verify them by simulations. We also find that the shorter adaptation latency of BIC TCP produces higher throughput than SACK TCP on vertical handoffs. Consequently, to get higher performance on vertical handoff situations, we propose to use BIC TCP.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.10 no.9
• /
• pp.2326-2333
• /
• 2009

In the adaptable bandwidth allocation technique, a transmission plan for variable rate video data is made by smoothing algorithms such as CBA algorithm and the data is sent by the transmission plan considering network traffic. But the CBA algorithm, the MCBA algorithm, MVBA algorithm and the other smoothing algorithms produce a transmission plan where the size of the increasing interval of transmission rate is generally larger than the size of the decreasing interval. And the transmission rate in CBA algorithm, the MCBA algorithm, the MVBA algorithm is changed in overflow curve during the increasing interval of transmission rate. This may cause many frames to be discarded when available transmission rate is larger than transmission rate by the transmission plan. In this paper, the smoothing algorithm, where transmission rate is changed in the middle of underflow curve and overflow curve to decrease the number of discarded frames, but the transmission rate increases at the minimum, and the CBA algorithm, the MCBA algorithm, the MVBA algorithm are applied to a transmission plan in the adaptable bandwidth allocation technique, and the minimum frame rates, the average frame rates, the variation of frame rates, and the numbers of discarded frames are compared in among algorithms.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.12 no.8
• /
• pp.1427-1433
• /
• 2008

There is SARLM scheme for dynamic adaptation to network congestion status which arises from multicast applications. However, in this scheme, when congestion occurs in a local, the waste of available bandwidth occurs in non-congestion local because of reducing of transmission rate in congestion local. In this paper, we propose a hierarchical multicast for dynamic adaptation to network congestion. In proposed scheme, we select a representative in each local. while congestion status. It receives packet from multicast sender and hierarchically transmits packet to the representative in congestion status by unicast for preventing decrease of transmission rate and the representative in congestion local transmits packet to the receivers in local by multicast. In experimental results, it was known that the proposed scheme could improve transmission rate of receivers in congestion status and more efficiently used available bandwidth.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.42 no.12
• /
• pp.149-158
• /
• 2005

This paper proposes a congestion avoidance algorithm which provides stable throughput and transmission rate regardless of buffer size by limiting the TCP congestion window in fixed bandwidth networks. Additive Increase, Multiplicative Decrease (AIMD) is the most commonly used congestion control algorithm. But, the AIMD-based TCP congestion control method causes unnecessary packet losses and retransmissions from the congestion window increment for available bandwidth verification when used in fixed bandwidth networks. In addition, the saw tooth variation of TCP throughput is inappropriate to be adopted for the applications that require low bandwidth variation. We present an algorithm in which congestion window can be limited under appropriate circumstances to avoid congestion losses while still addressing fairness issues. The maximum congestion window is determined from delay information to avoid queueing at the bottleneck node, hence stabilizes the throughput and the transmission rate of the connection without buffer and window control process. Simulations have performed to verify compatibility, steady state throughput, steady state packet loss count, and the variance of congestion window. The proposed algorithm can be easily adopted to the sender and is easy to deploy avoiding changes in network routers and user programs. The proposed algorithm can be applied to enhance the performance of the high-speed access network which is one of the fixed bandwidth networks.

• Journal of KIISE:Information Networking
• /
• v.29 no.6
• /
• pp.595-612
• /
• 2002

One of the most important issues in guaranteeing the high degree of QoS on mobile computing is how to reduce hand-off drops caused by lack of available bandwidth in a new cell. Each cell can request bandwidth reservation to its adjacent cells for hand-off calls. This reserved bandwidth can be used only for hand-offs, not for new calls. It is also important to determine how much of bandwidth should be reserved for hand-off calls because reserving too much would increase the probability of a new call being blocked. Therefore, it is essential to develop a new mechanism to provide QoS guarantee on a mobile computing environment by reserving an appropriate amount of bandwidth and call admission control. In this paper. bandwidth reservation and call admission control mechanisms are proposed to guarantee a consistent QoS for multimedia traffics on a mobile computing environment. For an appropriate bandwidth reservation, we propose an adaptive bandwidth reservation mechanism based on an MPP and a 2-tier cell structure. The former is used to predict a next move of the client while the latter to apply our mechanism only to the client with a high hand-off probability. We also propose a call admission control that performs call admission test only on PNC(Predicted Next Cell) of a client and its current cell. In order to minimize a waste of bandwidth caused by an erroneous prediction of client's location, we utilize a common pool and QoS adaptation scheme. In order evaluate the performance of our call admission control mechanism, we measure the metrics such as the blocking probability of new calls, dropping probability of hand-off calls, and bandwidth utilization. The simulation results show that the performance of our mechanism is superior to that of the existing mechanisms such as NR-CAT2, FR-CAT2, and AR-CAT2.

• Journal of Mechanical Science and Technology
• /
• v.20 no.1
• /
• pp.51-58
• /
• 2006

To compensate for the motion errors in hydrostatic tables, a method to actively control the clearance of a bearing corresponding to the amount of error using actively controlled capillaries is introduced in this paper. The design method for an actively controlled capillary that considers the output rate of a piezo actuator and the amount of error that must be corrected is described. The basic characteristics of such a system were tested, such as the maximum controllable range of the error, micro-step response, and available dynamic bandwidth when the capillary was installed in a hydrostatic table. The tests demonstrated that the maximum controllable range was $2.4\;{\mu}m$, the resolution was 27 nm, and the frequency bandwidth was 5.5 Hz. Simultaneous compensation of the linear and angular motion errors using two actively controlled capillaries was also performed for a hydrostatic table driven by a ballscrew and a DC servomotor. An iterative compensation method was applied to improve the compensation characteristics. Experimental results showed that the linear and angular motion errors were improved to $0.12{\mu}m$ and 0.20 arcsec, which were about $1/15^{th}$ and $1/6^{th}$ of the initial motion errors, respectively. These results confirmed that the proposed compensation method improves the motion accuracy of hydrostatic tables very effectively.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.3 no.4
• /
• pp.399-422
• /
• 2009

Although current wireless mesh network (WMN) applications experience a perceptually uninterrupted hand-off, their throughput after the hand-off event may be significantly degraded due to the low available bandwidth of the mobile client's new master. In this paper, we propose a novel mobility management scheme for 802.11-based WMNs that enables both seamless hand-off for transparent communications, and bandwidth awareness for stable application performance after the hand-off process. To facilitate this, we (i) present a new buffer moment in support of the fast Layer-2 hand-off mechanism to cut the packet loss incurred in the hand-off process to zero and (ii) design a dynamic admission control to grant joining accepts to mesh clients. We evaluate the benefits and drawbacks of the proposal for both UDP and TCP traffic, as well as the fairness of the proposal. Our results show that the new scheme can not only minimize hand-off latency, but also maintain the current application rates of roaming users by choosing an appropriate new master for joining.