• Journal of Korea Multimedia Society
• /
• v.18 no.2
• /
• pp.189-198
• /
• 2015

Despite the fact that traffic engineering techniques have been comprehensively utilized in the past to enhance the performance of communication networks, the distinctive characteristics of Software Defined Networking (SDN) demand new traffic engineering techniques for better traffic control and management. Considering the behavior of traffic, large flows normally carry out transfers of large blocks of data and are naturally packet latency insensitive. However, small flows are often latency-sensitive. Without intelligent traffic engineering, these small flows may be blocked in the same queue behind megabytes of file transfer traffic. So it is very important to identify large flows for different applications. In the scope of this paper, we present an approach to detect large flows in real-time without even a short delay. After the detection of large flows, the next problem is how to control these large flows effectively and prevent network jam. In order to address this issue, we propose an approach in which when the controller is enabled, the large flow is mitigated the moment it hits the predefined threshold value in the control application. This real-time detection, marking, and controlling of large flows will assure an optimize usage of an overall network.

• Journal of KIISE:Software and Applications
• /
• v.31 no.5
• /
• pp.643-650
• /
• 2004

Control flow graph is used for Performing many Program-analysis techniques, such as data-flow and control-dependence analysis, and software-engineering techniques, such as program slicing and testings. For these analyses to be safe and useful, the CFG should incorporate the exception flows that are induced by exceptions. In previous research to construct control flow graph, normal flows and exception flows are computed at the same time, since these two flows are known to be mutually dependent. By investigating realistic Java programs, we found that the cases when these two flows are mutually dependent rarely happen. So, we can decouple exception flow analysis from normal flow analysis. In this paper we propose an analysis that estimates exception flows. We also propose exception flow graph to represent exception flows. And we show that the control flow graph that accounts for exception flows can be constructed by merging exception flow graph onto normal control flow graph.

• Journal of Institute of Control, Robotics and Systems
• /
• v.8 no.4
• /
• pp.292-298
• /
• 2002

We focus on the slicing off some sub-nets using the transitive matrix. Control flows in the Petri nets is done based on the token flows. One control f]ow explains the independent tokens status and if the token-in divides into several tokens after firing a transition then the control flow divides to several flows, as well. Accordingly, we define that the basic unit of concur-rency (short BUC) is a set of the executed control flows based on the behavioral properties in the net. The BUC is S-invariant which has one control flow. We show the usefulness of transitive matrix to slice off some subnets from the original net based on BUC-through on an example.

• 유체기계공업학회:학술대회논문집
• /
• 2006.08a
• /
• pp.305-308
• /
• 2006

For controlling micro-flows inside a LOC (lab-on-a-chip) a syringe pump or an electronic device for EOF(electro-osmotic flow) have been used in general. However, these devices are so large and heavy that they are burdensome in the development of a portable micro-TAS (total analysis system). In this study, a new flow control system employing pressure chambers, digital switches and speed controllers was developed. This system could effectively control the micro-scale flows inside a LOC without any mechanical actuators or electronic devices We also checked the feasibility of this new control system by applying it to a LOC of micro-mixer type. Performance tests show that the developed control system has very good performance. Because the flow rate in LOC is controlled easily by throttling the speed controller, the flows in complicate microchannels network can be also controlled precisely.

• ETRI Journal
• /
• v.21 no.4
• /
• pp.23-28
• /
• 1999

In this paper, we analyze the performance benefits of broadband ATM networks when the call control and management flows are separated from user data flows. The virtual path tunneling concept for control and management flows are applied to the same physical ATM networks. The behaviors of channel throughput and transfer delay are analyzed. It results that the proposed virtual short-cut paths can maintain the network being stable with acceptable bandwidth. They are very useful to provide the stable control and management capabilities for Internet and mobile applications in the broadband ATM networks. In our numerical results, the effective throughputs of the proposed virtual shout-ut channel are about three times than those of end-to-end user data channels with hop distances of 10, and about two times than those with hop distance of 5 when the link blocking probability increases to 0.1. It concludes that the effective channel bandwidth are greatly reduced down while physical links are not stable and user traffic flows are occasionally overflowed.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.7
• /
• pp.2512-2531
• /
• 2014

We propose a new Distributed Denial of Service (DDoS) defense mechanism that protects http web servers from application-level DDoS attacks based on the two methodologies: whitelist-based admission control and busy period-based attack flow detection. The attack flow detection mechanism detects attach flows based on the symptom or stress at the server, since it is getting more difficult to identify bad flows only based on the incoming traffic patterns. The stress is measured by the time interval during which a given client makes the server busy, referred to as a client-induced server busy period (CSBP). We also need to protect the servers from a sudden surge of attack flows even before the malicious flows are identified by the attack flow detection mechanism. Thus, we use whitelist-based admission control mechanism additionally to control the load on the servers. We evaluate the performance of the proposed scheme via simulation and experiment. The simulation results show that our defense system can mitigate DDoS attacks effectively even under a large number of attack flows, on the order of thousands, and the experiment results show that our defense system deployed on a linux machine is sufficiently lightweight to handle packets arriving at a rate close to the link rate.

• ETRI Journal
• /
• v.5 no.2
• /
• pp.17-28
• /
• 1983

This paper deals with the problem of optimally controlling traffic flows in urban transportation traffic networks. For this, a nonlinear discrete-time model of urban traffic network is first suggested in order to handle the phenomenon of traffic flows such as oversaturatedness and/or undersaturatedness. Then an optimal control problem is formulated and a hierarchical optimization technique is applied, which is based upon a prediction-type two-level method of Hirvonen and Hakkala.

• ETRI Journal
• /
• v.30 no.2
• /
• pp.194-204
• /
• 2008

The online collection of coarse-grained traffic information, such as the total number of flows, is gaining in importance due to a wide range of applications, such as congestion control and network security. In this paper, we focus on an active queue management scheme called SRED since it estimates the number of active flows and uses the quantity to indicate the level of congestion. However, SRED has several limitations, such as instability in estimating the number of active flows and underestimation of active flows in the presence of non-responsive traffic. We present a Markov model to examine the capability of SRED in estimating the number of flows. We show how the SRED cache hit rate can be used to quantify the number of active flows. We then propose a modified SRED scheme, called hash-based two-level caching (HaTCh), which uses hashing and a two-level caching mechanism to accurately estimate the number of active flows under various workloads. Simulation results indicate that the proposed scheme provides a more accurate estimation of the number of active flows than SRED, stabilizes the estimation with respect to workload fluctuations, and prevents performance degradation by efficiently isolating non-responsive flows.

• Journal of Communications and Networks
• /
• v.11 no.3
• /
• pp.297-305
• /
• 2009

Multiprotocol label switching (MPLS) networks require dynamic flow admission control to guarantee end-to-end quality of service (QoS) for each Internet protocol (IP) traffic flow. In this paper, we propose to tackle the joint routing and admission control problem for the IP traffic flows in MPLS networks without rerouting already admitted flows. We propose two mathematical programming models for this problem. The first model includes end-to-end delay constraints and the second one, end-to-end packet loss constraints. These end-to-end QoS constraints are imposed not only for the new traffic flow, but also for all already admitted flows in the network. The objective function of both models is to minimize the end-to-end delay for the new flow. Numerical results show that considering end-to-end delay (or packet loss) constraints for all flows has a small impact on the flow blocking rate. Moreover, we reduces significantly the mean end-to-end delay (or the mean packet loss rate) and the proposed approach is able to make its decision within 250 msec.

• 한국전산유체공학회:학술대회논문집
• /
• 2003.10a
• /
• pp.86-87
• /
• 2003

Unstructured grid system is suitable for flows of complex geometries. For problems with moving boundary walls, the grid system must be changed and deformed with time if we use a body fitted grid system. In this paper, a new moving-grid finite-volume method on unstructured grid system is proposed and developed for unsteady compressible flows with shock waves. To assure geometric conservation laws on moving grid system, a control volume on the space-time unified domain is adopted for estimating numerical flux. The method is described and applied for two-dimensional flows.