Browsing by Subject "Telecommunication systems."

Now showing 1 - 5 of 5

Open Access
Multi-ring SDH network design over optical mesh networks
(2002) Tan, Tuba Akıncılar
The evolution of networks in telecommunications has brought on the importance of design techniques to obtain survivable and cost-effective transportation networks. In this thesis, we study Synchronous Digital Hierarchy (SDH) ring design problem with an interconnected multi-ring architecture overlaid over an optical mesh network. We decouple the problem into two sub-problems: the first problem is the SDH ring selection, and the second problem is the mapping of these rings onto the physical mesh topology. In this structure, the logical topology consists of SDH Add/Drop Multiplexers (ADMs) and Digital Cross-Connects (DXCs), and the physical topology consists of Optical Cross-Connects (OXCs). The ring selection problem is to choose the rings that give minimum inter-ring traffic in the network. Since inter-ring traffic increases the network cost and complexity, we aim to minimize the inter-ring traffic. We propose a greedy heuristic algorithm for this problem that finds a solution subject to the constraint that the number of nodes on each ring is limited. Numerical results on the ring design problem are presented for different topologies. Once the logical topology is obtained, resilient mapping of SDH rings onto the mesh physical topology is formulated as a Mixed Integer Linear Programming (MILP) problem. In order to guarantee proper operation of SDH ring protection against all single failures, each link on an SDH ring must be mapped onto a lightpath which is link and node disjoint from all other lightpaths comprising the same ring. The objective of this mapping is to minimize the total fiber cost in the network. We also apply a post-processing algorithm to eliminate redundant rings. The postprocessing algorithm is very useful to reduce the cost. We evaluate the performance of our design algorithm for different networks.
Open Access
Performance evaluation of telecommunication networks based on multi-regime fluid queues
(2009) Kankaya, Hüseyin Emre
Today’s state-of-the-art search engines utilize the inverted index data structure for fast text retrieval on large document collections. To parallelize the retrieval process, the inverted index should be distributed among multiple index servers. Generally the distribution of the inverted index is done in either a term-based or a document-based fashion. The performances of both schemes depend on the total number of disk accesses and the total volume of communication in the system. The classical approach for both distributions is to use the Central Broker Query Evaluation Scheme (CB) for parallel text retrieval. It is known that in this approach the central broker is heavily loaded and becomes a bottleneck. Recently, an alternative query evaluation technique, named Pipelined Query Evaluation Scheme (PPL), has been proposed to alleviate this problem by performing the merge operation on the index servers. In this study, we analyze the scalability and relative performances of the CB and PPL under various query loads to report the benefits and drawbacks of each method.
Open Access
Performance modeling of communication networks offered with a mixture of persistent TCP and UDP flows
(2013) Çalış, Gökhan
A damped fixed-point approximation is proposed to characterize the throughput of persistent TCP and UDP flows in a network of router links supporting per-class queuing and Deficit Round Robin (DRR) scheduling among classes. In particular, we study the case of two classes where one of the classes uses drop-tail queue management and is intended for UDP traffic. The other class targeting TCP traffic is assumed to use Active Queue Management (AQM). The effectiveness of the proposed analysis method in this scenario is validated by extensive NS3 simulations. Moreover, we study, using the proposed fixed-point algorithm, the potential gain of employing the many-to-one communications paradigm with respect to the conventional one-to-one communications in which a client downloads a specific content from one server only.
Open Access
Placement of express links in a DWDM optical network
(2005) Şöhret, Oğuz
With the introduction of DWDM technology in telecommunication network systems, important advancements have been achieved in the problem of routing the increasing signal traffic between demand-supply nodes. The choice of the links to open, the number of links and routing of current traffic on these links in such an optical network system are important in terms of decreasing the complexity of the network and cost savings. The study in this thesis firstly introduces the use of express links, which enables those objectives, and then determines the appropriate network structure and routing. The study introduces two mathematical models as well as a lagrangian based heuristic for the solution of the problem.
Open Access
Stochastic signaling for power constrained communication systems
(2011) Göken, Çağrı
In this thesis, optimal stochastic signaling problem is studied for power constrained communications systems. In the first part, optimal stochastic signaling problem is investigated for binary communications systems under second and fourth moment constraints for any given detector structure and noise probability distribution. It is shown that an optimal signal can be represented by randomization among at most three signal levels for each symbol. Next, stochastic signaling problem is studied in the presence of an average power constraint instead of second and fourth moment constraints. It is shown that an optimal signal can be represented by randomization between at most two signal levels for each symbol in this case. For both scenarios, sufficient conditions are obtained to determine the improvability and nonimprovability of conventional deterministic signaling via stochastic signaling. In the second part of the thesis, the joint design of optimal signals and optimal detector is studied for binary communications systems under average power constraints in the presence of additive non-Gaussian noise. It is shown that the optimal solution involves randomization between at most two signal levels and the use of the corresponding maximum a posteriori probability (MAP) detector. In the last part of the thesis, stochastic signaling is investigated for power-constrained scalar valued binary communications systems in the presence of uncertainties in channel state information (CSI). First, stochastic signaling is performed based on the available imperfect channel coef- ficient at the transmitter to examine the effects of imperfect CSI. The sufficient conditions are derived for improvability and nonimprovability of deterministic signaling via stochastic signaling in the presence of CSI uncertainty. Then, two different stochastic signaling strategies, namely, robust stochastic signaling and stochastic signaling with averaging, are proposed for designing stochastic signals under CSI uncertainty. For the robust stochastic signaling problem, sufficient conditions are derived to obtain an equivalent form which is simpler to solve. In addition, it is shown that optimal signals for each symbol can be written as randomization between at most two signal levels for stochastic signaling using imperfect channel coefficient and stochastic signaling with averaging as well as for robust stochastic signaling under certain conditions. The solutions of the optimal stochastic signaling problems are obtained by using global optimization techniques, specifically, Particle Swarm Optimization (PSO), and by employing convex relaxation approaches. Numerical examples are presented to illustrate the theoretical results at the end of each part.