Browsing by Subject "Queueing networks"

Now showing 1 - 12 of 12

Open Access
AIMD-based online MPLS traffic engineering for TCP flows via distributed multi-path routing
(Springer, 2004) Alparslan O.; Akar, N.; Karasan, E.
With this paper, we propose a distributed online traffic engineering architecture for MPLS networks. In this architecture, a primary and secondary MPLS LSP are established from an ingress LSR to every other egress LSR. We propose to split the TCP traffic between the primary and secondary paths using a distributed mechanism based on ECN marking and AIMD-based rate control. Inspired by the random early detection mechanism for active queue management, we propose a random early reroute scheme to adaptively control the delay difference between the primary and secondary LSPS. Considering the adverse effect of packet reordering on TCP performance for packet-based load balancing schemes, we propose that the TCP splitting mechanism operates on a per-flow basis. Using flow-based models developed for Internet traffic and simulations, we show that flow-based distributed multi-path traffic engineering outperforms on a consistent basis the case of a single path in terms of per-flow goodputs. Due to the elimination of out-of-order packet arrivals, flow-based splitting also enhances TCP performance with respect to packet-based splitting especially for long TCP flows that are hit hard by packet reordering. We also compare and contrast two queuing architectures for differential treatment of data packets routed over primary and secondary LSPS in the MPLS data plane, namely first-in-first-out and strict priority queuing. We show through simulations that strict priority queuing is more effective and relatively more robust with respect to the changes in the traffic demand matrix than first-in-first-out queuing in the context of distributed multi-path routing.
Open Access
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.
Open Access
Comparison of PI controllers designed for the delay model of TCP/AQM networks
(Elsevier, 2013) Ünal H. U.; Melchor-Aguilar, D.; Üstebay, D.; Niculescu, S. -I.; Özbay, Hitay
One of the major problems of communication networks is congestion. In order to address this problem in TCP/IP networks, Active Queue Management (AQM) scheme is recommended. AQM aims to minimize the congestion by regulating the average queue size at the routers. To improve upon AQM, recently, several feedback control approaches were proposed. Among these approaches, PI controllers are gaining attention because of their simplicity and ease of implementation. In this paper, by utilizing the fluid-flow model of TCP networks, we study the PI controllers designed for TCP/AQM. We compare these controllers by first analyzing their robustness and fragility. Then, we implement these controllers in ns-2 platform and conduct simulation experiments to compare their performances in terms of queue length. Taken together, our results provide a guideline for choosing a PI controller for AQM given specific performance requirements.
Open Access
Componentwise bounds for nearly completely decomposable Markov chains using stochastic comparison and reordering
(Elsevier, 2005) Pekergin, N.; Dayar T.; Alparslan, D. N.
This paper presents an improved version of a componentwise bounding algorithm for the state probability vector of nearly completely decomposable Markov chains, and on an application it provides the first numerical results with the type of algorithm discussed. The given two-level algorithm uses aggregation and stochastic comparison with the strong stochastic (st) order. In order to improve accuracy, it employs reordering of states and a better componentwise probability bounding algorithm given st upper- and lower-bounding probability vectors. Results in sparse storage show that there are cases in which the given algorithm proves to be useful. © 2004 Elsevier B.V. All rights reserved.
Open Access
A matrix analytical method for the discrete time Lindley equation using the generalized Schur decomposition
(ACM, 2006) Akar, Nail
In this paper, we study the discrete time Lindley equation governing an infinite size GI/GI/1 queue. In this queuing system, the arrivals and services are independent and identically distributed but they obey a discrete time matrix geometric distribution not necessarily with finite support. Our GI/GI/1 model allows geometric batch arrivals and also treats late, early, and hybrid arrival models in a unified manner. We reduce the problem of finding the steady state probabilities for the Lindley equation to finding the generalized ordered Schur form of a matrix pair (E, A) where the size of these matrices are the sum, not the product, of the orders of individual arrival and service distributions. The approach taken in this paper is purely matrix analytical and we obtain a matrix geometric representation for the related quantities (queue lengths or waiting times) for the discrete time GI/GI/1 queue using this approach.
Open Access
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.
Open Access
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.
Open Access
Solving the single server semi-Markov queue with matrix exponential kernel matrices for interarrivals and services
(ACM, 2006) Akar, Nail; Sohraby, K.
Markov renewal processes with semi-Markov kernel matrices that have matrix-exponential representations form a superset of the well-known phase-type renewal process, Markovian arrival process, and the recently introduced rational arrival process. In this paper, we study the steady-state waiting time distribution in an infinite capacity single server queue with the auto-correlation in interarrival and service times modeled with this general Markov renewal process. Our method relies on the algebraic equivalence between this waiting time distribution and the output of a feedback control system certain parameters of which are to be determined through the solution of a well known numerical linear algebra problem, namely the SDC (Spectral-Divide-and- Conquer) problem. We provide an algorithmic solution to the SDC problem and in turn obtain a simple matrix exponential representation for the waiting time distribution using the ordered Schur decomposition that is known to have numerically stable and efficient implementations in various computing platforms.
Open Access
Switching resilient PI controllers for active queue management of TCP flows
(IEEE, 2007) Üstebay, Deniz; Özbay, Hitay
Active Queue Management (AQM) is used in computer networks to increase link utilization with less queueing delays. The fluid flow model or TCP based on delay differential equations supplies the mathematical background for modelling the AQM as a feedback system. Recently various PI and PID controllers arr designed for this feedback system, [7], [18]. In this paper, we consider the case for which the Round Trip Time (RTT) is time varying and we propose switching resilient PI controllers using the design method introduced in [18].
Open Access
TELPACK: An Advanced teletraffic analysis package
(1998) Akar, N.; Oguz, N.C.; Sohraby, K.
Performance evaluation of computer and communication networks gives rise to teletraffic problems of potentially large dimensionality. We briefly summarize a unifying system theoretic approach to efficient solution of a diversity of such problems, and introduce TELPACK, a publicly available software that implements this approach.
Open Access
Uniform weighted round robin scheduling algorithms for input queued switches
(IEEE, 2001-06) Rai, Idris A.; Alanyalı, Murat
This paper concentrates on obtaining uniform weighted round robin schedules for input queued packet switches. The desired schedules are uniform in the sense that each connection is serviced at regularly spaced time slots, where the spacing is proportional to the inverse of the guaranteed data rate. Suitable applications include ATM networks as well as satellite switched TDMA systems that provide per packet delay guarantees. Three heuristic algorithms are proposed to obtain such schedules under the constraints imposed by the unit speedup of input queued switches. Numerical experiments indicate that the algorithms have remarkable performance in finding uniform schedules.
Open Access
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.