Browsing by Subject "Quality of service"

Now showing 1 - 11 of 11

Open Access
Client-server synchronization and buffering for variable rate multimedia retrievals
(1996) Hui J.Y.; Karasan, E.; Li J.; Zhang, J.
We consider the use of large buffers and feedback as a mechanism to maintain loosely coupled synchronization between a multimedia server and a client. The multimedia stream is modeled as a fluid flow through rate controlled valves and buffers with multiple thresholds. These thresholds are used to control the rates upstream. The quality of service for the multimedia connection is characterized in terms of the jitter in the received media stream due to buffer underflow and overflow. This quality of service is used to exercise rate and admission control in the presence of congestion. The feedback mechanism is, implemented in GRAMS, an adaptive multimedia client-server system. Experimental statistics are gathered for the purpose of traffic engineering. We employ a fluid flow and first passage time analysis to understand the traffic process through the pipelines and the buffers and to estimate the amount of signaling required by the feedback mechanism.
Open Access
Effect of burst length on loss probability in OBS networks with void-filling scheduling
(2006) Kamçı, Ahmet Kerim
Optical burst switching (OBS) is a new transport architecture for the next generation optical internet infrastructure which is necessary for the increasing demand of high speed data traffic. Optical burst switching stands between optical packet switching, which is technologically difficult, and optical circuit switching, which is not capable of efficiently transporting bursty internet traffic. Apart from its promising features, optical burst switching suffers from high traffic blocking probabilities. Wavelength conversion coupled with fiber delay lines (FDL) provide one of the best means of contention resolution in optical burst switching networks. In this thesis, we examine the relation between burst loss probability and burst sizes for void filling scheduling algorithms. Simulations are performed for various values of the processing and switching times and for different values of wavelengths per fiber and FDL granularity. The main contribution of this thesis is the analysis of the relationship between burst sizes and processing time and FDL induced voids. This in turn creates a better understanding of the burstification and contention resolution mechanisms in OBS networks. We show that voids generated during scheduling are governed by the FDL granularity and the product of the per-hop processing delay and residual number of hops until the destination. We also show that differentiation between bursts with different sizes is achieved for different network parameters and a differentiation mechanism based on burst lengths is proposed for OBS networks.
Open Access
Exact calculation of blocking probabilities for bufferless optical burst switched links with partial wavelength conversion
(IEEE, 2004-10) Akar, Nail; Karasan, Ezhan
In this paper, we study the blocking probabilities in a wavelength division multiplexing-based asynchronous bufferless optical burst switch equipped with a bank of tuneable wavelength converters that is shared per output link. The size of this bank is generally chosen to be less than the number of wavelengths on the link because of the relatively high cost of wavelength converters using current technologies; this case is referred to as partial wavelength conversion in the literature. We present a probabilistic framework for exactly calculating the blocking probabilities. Burst durations are assumed to be exponentially distributed. Burst arrivals are first assumed to be Poisson and later generalized to the more general phase-type distribution. Unlike existing literature based on approximations and/or simulations, we formulate the problem as one of finding the steadystate solution of a continuous-time Markov chain with a block tridiagonal infinitesimal generator. We propose a numerically efficient and stable solution technique based on block tridiagonal LU factorizations. We show that blocking probabilities can exactly and efficiently be found even for very large systems and rare blocking probabilities. Based on the results of this solution technique, we also show how this analysis can be used for provisioning wavelength channels and converters. © 2004 IEEE.
Open Access
H∞-performance analysis of robust controllers designed for AQM
(IEEE, 2003) Yan, P.; Özbay, Hitay
It has been shown that the TCP connections through the congested routers with the Active Queue Management (AQM) can be modeled as a nonlinear feedback system. In this paper, we design H∞ robust controllers for AQM based on the linearized TCP model with time delays. For the linear system model exhibiting LPV nature, we investigate the H∞-performance with respect to the uncertainty bound of RTT (round trip time). The robust controllers and the corresponding analysis of H∞-performance are validated by simulations in different scenarios.
Open Access
Impact of scalability in video transmission in promotion-capable differentiated services networks
(IEEE, 2002-09) Gürses, E.; Akar, G. B.; Akar, Nail
Transmission of high quality video over the Internet faces many challenges including unpredictable packet loss characteristics of the current Internet and the heterogeneity of receivers in terms of their bandwidth and processing capabilities. To address these challanges, we propose an architecture in this paper that is based on the temporally scalable and error resilient video coding mode of the H.263+ codec. In this architecture, the video frames will be transported over a new generation IP network that supports differentiated services (Diffserv). We also propose a novel Two Rate Three Color Promotion-Capable Marker (trTCPCM) to be used at the edge of the diffserv network. Our simulation study demonstrates that an average of 30 dB can be achieved in case of highly congested links.
Open Access
Performance analysis of two-level forward error correction for lostcell recovery in ATM networks
(IEEE, 1995-04) Oğuz, Nihat Cem; Ayanoğlu, E.
The major source of errors in B-ISDN/ATM systems is expected to be buffer overflow during congested conditions, resulting in ATM cell losses which degrade the quality of service. It has been shown by many authors that the performance of the end-to-end system can be made much less sensitive to cell loss by means of forward error correction. This paper discusses the use of a two-level forward error correction scheme for virtual channel and virtual path connections in ATM networks. The scheme exploits simple block coding and code interleaving simultaneously. The simple block, interleaved, and joint coding schemes are studied and analyzed by using a novel and accurate discrete-time analytical method which enables the burstiness of cell losses be captured precisely. Detailed performance calculations, which indicate that it is possible to reduce the cell loss rate by several orders of magnitude over a wide range of network load for various traffic conditions, are discussed, and compared with simulation results. The comparisons show that the method is very accurate for bursty traffic. The advantages of the three coding techniques are quantified for different traffic characteristics and scenarios © Copyright 2009 IEEE - All Rights Reserved.
Open Access
A reordering-free multipath traffic engineering architecture for DiffServ-MPLS networks
(IEEE, 2003-10) Akar, Nail; Hokelek, İbrahim; Atik, Muammer; Karasan, Ezhan
We propose a novel traffic engineering architecture for IP networks with multiprotocol label switching (MPLS) backbones. In this architecture, two (primary and secondary) label switched paths (LSPs) are established among every pair of IP routers located at the edge of an MPLS cloud. Traffic between a source-destination pair is then split between the primary and secondary LSPs using an ABR-like explicit-rate feedback gathered from the network. Taking into consideration the packet reordering effect of packet-based load balancing schemes, we propose a novel traffic splitting mechanism that operates on a per-flow basis. We show, using a variety of scenarios, that deploying flow-based multipath traffic engineering not only provides significantly and consistently better throughput than that of a single path, but is also void of any packet reordering. © 2003 IEEE.
Open Access
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.
Open Access
Short-range wireless communications and reliability
(Cambridge University Press, 2011) Güvenç, İ.; Gezici, Sinan; Şahinoğlu, Z.; Kozat, U. C.; Güvenç, İ.; Gezici, Sinan; Şahinoğlu, Z.; Kozat, U. C.
Even though there is no universally accepted definition, short-range wireless communications typically refers to a wide variety of technologies with communication ranges from a few centimeters to several hundreds of meters. While the last three decades of the wireless industry have been mostly dominated by cellular systems, short-range wireless devices have gradually become a more integrated part of our everyday lives over the last decade. The Wireless World Research Forum (WWRF) envisions that this trend will accelerate in the upcoming years: by the year 2017, it is expected that seven billion people in the world will be using seven trillion wireless devices [1]. The majority of these devices will be short-range wireless devices that interconnect people with each other and their environments. While the reliability of wireless communication systems has been studied in detail in the past, a comprehensive study of different factors affecting reliability for short-range wireless systems and how they can be handled is not available in the literature, to date. The present book intends to fill this gap by covering important reliability problems for short-range wireless communication systems. The scope of the contributions in the book is mostly within the domain of wireless personal area networks (WPANs) and wireless sensor networks (WSNs), and issues related to wireless local area networks (WLANs) are not specifically treated. Due to the differences in application scenarios, quality of service (QoS) requirements, signaling models, and different error sources and mitigation approaches, the high-rate and low-rate systems will be addressed in separate parts of the book.
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
Star p-hub center problem and star p-hub median problem with bounded path lengths
(2012) Yaman H.; Elloumi, S.
We consider two problems that arise in designing two-level star networks taking into account service quality considerations. Given a set of nodes with pairwise traffic demand and a central hub, we select p hubs and connect them to the central hub with direct links and then we connect each nonhub node to a hub. This results in a star/star network. In the first problem, called the Star p-hub Center Problem, we would like to minimize the length of the longest path in the resulting network. In the second problem, Star p-hub Median Problem with Bounded Path Lengths, the aim is to minimize the total routing cost subject to upper bound constraints on the path lengths. We propose formulations for these problems and report the outcomes of a computational study where we compare the performances of our formulations.