Browsing by Subject "QoS"
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Item Open Access Analytical modeling of multi-channel optical burst switching with multiple traffic classes(Bilkent University, 2011) Dinç, VolkanIn this thesis, we study an Optical Burst Switching (OBS) node with links carrying multiple wavelength channels (called hereafter channels) with multiple traffic classes. We assume that offset-based service differentiation is used to differentiate among these traffic classes in terms of packet loss probabilities. We first propose a basic scheme, called bLAUC (Basic Latest Available Unused Channel) for channel scheduling. Although practicality of the bLAUC scheme is relatively limited when compared to other conventional schedulers such as LAUC, we study bLAUC in this thesis due to its tractability to analysis and moreover bLAUC possesses certain crucial properties of conventional schedulers. We then propose an iterative procedure to approximate per-class loss probabilities for the OBS link of interest when packet arrivals to the link are Poisson and packet lengths are exponentially distributed. In our iterative procedure, we model a multi-channel OBS link with Poisson arrivals by a single channel Markov fluid queue with occupancy-dependent packet arrival intensities. The proposed procedure provides acceptable approximations for a wide range of scenarios with relatively low complexity. Consequently, the proposed procedure can be used in optimization problems concerning multiclass OBS and in finding guidelines to effectively utilize OBS resources under loss probability constraints.Item Open Access A dynamic DRR scheduling algorithm for flow level QOS assurances for elastic traffic(Bilkent University, 2006) Kurugöl, SılaBest effort service, used to transport the Internet traffic today, does not provide any QoS assurances. Intserv, DiffServ and recently proposed Proportional Diff- Serv architectures have been introduced to provide QoS. In these architectures, some applications with more stringent QoS requirement such as real time traffic are prioritized, while elastic flows share the remaining bandwidth. As opposed to the well studied differential treatment of delay and/or loss sensitive traffic to satisfy QoS constraints, our aim is satisfy QoS requirements of elastic traffic at the flow level. We intend to maintain different average rate levels for different classes of elastic traffic. For differential treatment of elastic flows, a dynamic variant of Deficit Round Robin Scheduler (DRR) is used as oppose to a FIFO queue. In this scheduling algorithm, all classes are served in a round robin fashion in proportion to their weights at each round. The main difference of our scheduler from the original DRR scheduler is that, we update the weights, which are called quantums of the scheduler at each round in response to the feedback from the network, which is in terms of the rate of phantom connection sharing capacity fairly with the other flows in the same queue. According to the rate measured in the last time interval, the controller updates the weights in proportion with the bandwidth requirements of each class to satisfy their QoS requirements, while the remaining bandwidth will be used by the best effort traffic. In order to find an optimal policy for the controller a simulation-based learning algorithm is performed using a processor sharing model of TCP, then the resultant policies are applied to a more realistic scenario to solve Dynamic DRR scheduling problem through ns-2 simulations.Item Open Access A performance evaluation framework of a rate-controlled MPEG video transmission over UMTS networks(IEEE, 2007-07) Akar, Nail; Barbera, M.; Budzisz, L.; Ferrùs, R.; Kankaya, Emre; Schembra, G.UMTS is designed to offer high bandwidth radio access with QoS assurances for multimedia communications. In particular, real-time video communications services are expected to become a successful experience under UMTS networks. In this context, a video transmission service can be designed over the basis that UMTS can provide either a constant bit rate data channel or a dynamic variable bit rate data channel adapted to load conditions. In this latter approach, which is more efficient for both the user and the service provider, multimedia sources have to be timely designed in order to adapt their output rate to the instantaneous allowed channel rate. The target of this paper is to define an analytical model of adaptive real-time video sources in a UMTS network where system resources are dynamically shared among active users. © 2007 IEEE.Item Open Access Performance evaluation of slotted optical burst switching systems with quality of service differentiation(Institute of Electrical and Electronics Engineers, 2009) Ozturk, O.; Karasan, E.; Akar, N.Slotted optical burst switching (SOBS) has recently caught the attention of the optical networking community due to performance gains achievable with synchronous infrastructures. In this paper, we study the loss probabilities in a slotted optical burst switching node fed with Poisson burst traffic where the fixed burst size is an integer multiple of the slot length. We develop a discrete-time Markov chain (DTMC) based framework to obtain the loss probabilities in systems with and without quality of service (QoS) differentiation. In particular, we focus on analytical modeling of priority scheduling and offset-based QoS differentiation mechanisms for SOBS networks. The latter problem suffers from the curse of dimensionality which we address by a discrete phase type distribution approximation for the discrete Poisson distribution leading to an accurate approximation for the loss probabilities. A hybrid QoS mechanism which jointly utilizes offset-based differentiation together with priority scheduling is also analyzed. © 2009 IEEE.