Browsing by Subject "Active queue management"

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    Analysis of an Adaptive Modulation and Coding scheme with HARQ for TCP traffic
    (IEEE, 2015-04) Öztürk, Onur; Akar, Nail
    In this paper, we analyze the aggregate TCP throughput performance of a wireless link utilizing Active Queue Management (AQM) and an Adaptive Modulation and Coding (AMC) scheme with Hybrid ARQ (HARQ) based on the probability of failure in the first transmission attempt. We assume packets arriving out-of-order at the wireless receiver due to random retransmissions are resequenced before being released to the network. For this reason, an approximate model for the delay experienced at the resequencing buffer is also presented. In the light of the results obtained from the presented analysis, we propose a threshold for the aforementioned probability of failure making the investigated AMC scheme work at an overall performance close to that of the optimum policy. © 2015 IEEE.
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    Fixed-point analysis of a network of routers with persistent TCP/UDP flows and class-based weighted fair queuing
    (Springer New York LLC, 2017) Tunc C.; Akar, N.
    Fixed-point models have already been successfully used to analytically study networks consisting of persistent TCP flows only, or mixed TCP/UDP flows with a single queue per link and differentiated buffer management for these two types of flows. In the current study, we propose a nested fixed-point analytical method to obtain the throughput of persistent TCP and UDP flows in a network of routers supporting class-based weighted fair queuing allowing the use of separate queues for each class. In particular, we study the case of two classes where one of the classes uses drop-tail queue management and is intended for only UDP traffic. The other class targeting TCP, but also allowing UDP traffic for the purpose of generality, is assumed to employ active queue management. The effectiveness of the proposed analytical method is validated in terms of accuracy using ns-3 simulations and the required computational effort.
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    A new PI and PID control design method for integrating systems with time delays: applications to AQM of TCP flows
    (World Scientific and Engineering Academy and Society (WSEAS), 2007-02) Üstebay, Deniz; Özbay, Hitay; Gündeş, N.
    Allowable PI and PD controller gains for a class of unstable MIMO systems with input/output delays have been investigated in [5, 12]. Using the results of these studies, we propose a new method for tuning the parameters of PI and PID controllers for integrating processes with time delays. As an application of this method, we design PI and PID controllers for Active Queue Management,of TCP flows and illustrate performance,of these controllers by packet level simulations in ns-2. Key‐Words: PID Controllers, Time Delay, Integrating Processes, Active Queue Management
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    A novel queue-aware wireless link adaptation mechanism and its fixed-point analytical model
    (SpringerOpen, 2015) Ozturk, O.; Akar, N.
    A point-to-point (PTP) wireless link is studied that carries long-lived TCP flows and is controlled with active queue management (AQM). A cross-layer queue-aware adaptive modulation and coding (AMC)-based link adaptation (LA) mechanism is proposed for this wireless link to improve the TCP-level throughput relative to the case where AMC decisions are made based solely on the physical layer (PHY) parameters. The proposed simple-to-implement LA mechanism involves the use of an aggressive modulation and coding scheme (MCS) with high spectral efficiency and high block error rates when the queue occupancy exceeds a certain threshold, but otherwise a relatively conservative MCS with lower spectral efficiency and lower block error rates. A fixed-point analytical model is proposed to obtain the aggregate TCP throughput attained at this wireless link and the model is validated by ns-3 simulations. Numerical experimentation with the proposed analytical model applied to an IEEE 802.16-based wireless link demonstrates the effectiveness of the proposed queue-aware LA (QAWLA) mechanism in a wide variety of scenarios including cases where the channel information is imperfect. The impact of the choice of the queue occupancy threshold of QAWLA is extensively studied with respect to the choice of AQM parameters in order to provide engineering guidelines for the provisioning of the wireless link.
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    On the design of AQM supporting TCP flows using robust control theory
    (IEEE, 2004) Quet, P-F.; Özbay, Hitay
    Recently it has been shown that the active queue management schemes implemented in the routers of communication networks supporting transmission control protocol (TCP) flows can be modeled as a feedback control system. Based on a delay differential equations model of TCPs congestion-avoidance mode different control schemes have been proposed. Here a robust controller is designed based on the known techniques for H∞ control of systems with time delays.
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    On the design of AQM supporting TCP flows using robust control theory
    (IEEE, 2003) Quet, P. F.; Özbay, Hitay
    Recently it has been shown that the AQM (Active Queue Management) schemes implemented in the routers of communication networks supporting TCP (Transmission Control Protocol) flows can be modeled as a feedback control system. Based on a delay differential equations model of TCP's congestion-avoidance mode different control schemes have been proposed. Here a robust controller is designed based on the known techniques for ℋ ∞ control of systems with time delays.
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    Performance modeling and analysis of the interplay among Tcp, active queue management and wireless link adaptation
    (2015-09) Öztürk, Onur
    We propose a novel workload-dependent queuing model of a wireless router link which employs active queue management and is offered with a number of persistent TCP flows. As opposed to existing work that focus only on the average queue occupancy as the performance metric of interest, the proposed analytical method obtains the more informative steady-state queue occupancy distribution of the wireless link. With the intention of maximizing TCP throughput, this analytical method is used to study traffic agnostic link adaptation schemes with and without hybrid ARQ. Moreover, a novel cross-layer queue-aware link adaptation scheme is proposed to improve the TCP throughput relative to the case where adaptive modulation and coding decisions are made based solely on the physical layer parameters. A fixed-point analytical model is proposed to obtain the aggregate TCP throughput attained at wireless links employing active queue management and queue-aware link adaptation. Allowing packet retransmissions and generalizing the scope from a single link to a network of such links, we propose an energy efficient queue-aware link adaptation scheme with hybrid ARQ which jointly adapts the transmission power and rate of the wireless links based on the queue occupancy levels and the channel conditions. Furthermore, we provide a fixed-point analytical method for such networks.
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    Robust controller design for AQM and H∞-performance analysis
    (Springer, 2005) Yan, P.; Özbay, Hitay
    Active Queue Management (AQM) has recently been proposed in [1] to support the end-to-end congestion control for TCP traffic regulation on the Internet. For the purpose of alleviating congestion for IP networks and providing some notion of quality of service (QoS), the AQM schemes are designed to improve the Internet applications. Earliest efforts on AQM (e.g. RED in [2]) are essentially heuristic without systematic analysis. The dynamic models of TCP ([9, 12]) make it possible to design AQM using feedback control theory. We refer to [11] for a general review of Internet congestion control.
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    Variable structure control in active queue management for TCP with ECN
    (IEEE, 2003) Yan, P.; Gao, Y.; Özbay, Hitay
    It has been shown that the TCP connections through the congested routers can be modeled as a feedback dynamic system. In this paper, we design a variable structure (VS) based control scheme in active queue management (AQM) supporting explicit congestion notification (ECN). By analyzing the robustness and performance of the control scheme for nonlinear TCP/AQM model, we show that the proposed design has good performance and robustness with respect to the uncertainties of the round-trip time (RTT) and the number of active TCP sessions, which are central to the notion of AQM. Implementation issues are discussed and ns simulations are provided to validate the design and compare its performance to other peer schemes' in different scenarios. The results show that the proposed design significantly outperforms the peer AQM schemes in terms of packet loss ratio, throughput and buffer fluctuation.