Multi-service communications networks are generally designed, provisioned and configured, based on source-destination user demands expected to occur over a recurring time period. However due to network users' actions being non-deterministic, actual user demands will vary from those expected, potentially causing some network resources to be under- provisioned, with others possibly over-provisioned. As actual user demands vary over the recurring time period from those expected, so the status of the various shared network resources may also vary. This high degree of uncertainty necessitates using adaptive resource allocation mechanisms to share the finite network resources more efficiently so that more of actual user demands may be accommodated onto the network. The overhead for these adaptive resource allocation mechanisms must be low in order to scale for use in large networks carrying many source-destination user demands. This thesis examines the use of stochastic learning automata for the adaptive routing problem (these being adaptive, distributed and simple in implementation and operation) and seeks to improve their weakness of slow convergence whilst maintaining their strength of subsequent near optimal performance. Firstly, current reinforcement algorithms (the part causing the automaton to learn) are examined for applicability, and contrary to the literature the discretised schemes are found in general to be unsuitable. Two algorithms are chosen (one with fast convergence, the other with good subsequent performance) and are improved through automatically adapting the learning rates and automatically switching between the two algorithms. Both novel methods use local entropy of action probabilities for determining convergence state. However when the convergence speed and blocking probability is compared to a bandwidth-based dynamic link-state shortest-path algorithm, the latter is found to be superior. A novel re-application of learning automata to the routing problem is therefore proposed: using link utilisation levels instead of call acceptance or packet delay. Learning automata now return a lower blocking probability than the dynamic shortest-path based scheme under realistic loading levels, but still suffer from a significant number of convergence iterations. Therefore the final improvement is to combine both learning automata and shortest-path concepts to form a hybrid algorithm. The resulting blocking probability of this novel routing algorithm is superior to either algorithm, even when using trend user demands.

Chemnitz, Techn. Univ., Diplomarb., 2001.

No description available.

No description available.

This thesis is a study on the issues involved in implementing asynchronous transfer mode (ATM) over satellite links and the ways in which ATM can be optimised to achieve better performance over such links. The main issue is the impact of errors introduced by the satellite links on the performance of ATM. Options to improve the performance of ATM over SATCOM have been identified and they are: (i) increase transmit power, (ii) FEC, (iii) adoption of an alternative ATM architecture, (iv) extensive to commercial-off-the-shelf (COTS) ATM equipments and (v) construction of ATM protocol enhancers. The fifth option which uses a combination of protocol conversions and error control techniques is preferred over the others as it allows maximum use of standard COTS ATM equipments and provides a framework for experimentation with multiple versions of ATM equipments (that are evolving rapidly). As part of the strategy of using protocol enhancement to improve the performance of ATM, two techniques have been proposed. The first technique is called cell header duplication, and it improves cell loss ratio by compressing the information in the cell headers and using the extra room in each header to carry the duplicate compressed header information of the previous cell. When a cell header is corrupted, the corrupted header information is replaced with the duplicate copy carried in the next cell, provided that too is not corrupted. This technique was compared with cell header interleaving and error tolerant addressing which are cell header protection techniques proposed by others. The second technique is called selective cell retransmission, which employs a partial retransmission (hybrid) ARO strategy to perform error recovery for only the individually errored non-realtime cells allowing it to achieve higher reliability of data transfer and more efficient utilisation of satellite bandwidth. The overhead in the proposed scheme varies according to the error conditions in the satellite channel making it an adaptive system. This is achieved by using a unique method of sending error erasure information (inserted into cells carrying negative acknowledgement messages) from the receiver to the transmitter which will use this information to pin-point the corrupted cells. The scheme is also compared with concatenated coding (using a Reed-Solomon code) and link protocols (using selective repeat (full retransmission) ARQ).

Stuttgart, Univ., Fakultät Informatik, Diplomarb., 1997.

Stuttgart, Univ., Diplomarb., 1999.

Universiẗat, Diss., 1999--Hamburg.

Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. / Made available in DSpace on 2012-10-17T08:56:59Z (GMT). No. of bitstreams: 0Bitstream added on 2016-01-08T23:56:37Z : No. of bitstreams: 1 137680.pdf: 10352301 bytes, checksum: d6bfc944e5756b919f0aa03433f696ae (MD5)

Debido a la crisis económica surgida en los últimos años, las empresas se ven en la necesidad de ahorrar costos logísticos, costos de operación, costos financieros y demás costos que incurren en las operaciones. Como profesional en Ingeniería Industrial bajo la misión de generar valor a las operaciones y rentabilizar los negocios de la empresa a través de las herramientas adquiridas durante la carrera, presenté una propuesta de mejora a la Gerencia Central de Operaciones y a la Gerencia General de la Cia. PROSEGUR SA, la optimización de recursos para la atención de los servicios de cajeros automáticos ATM. Teniendo como precedente que hace 20 años debido al terrorismo, y zonas de alto riesgo de los cajeros ATM, escasa ayuda del sistema de información, inexistencia de la seguridad electrónica, los cajeros ATM eran victimas constantes de robos y asaltos. Fue así que se decidió operar estos servicios con un cuarto hombre que realice la actividad de segundo resguardo de valores dentro de la Unidad Blindad, por la sencilla razón que más hombres de seguridad le permitía tener mayor seguridad en las operaciones en una época de alta peligrosidad. Esto supone generar gastos que ascienden a 221,000 dólares anuales aprox., atentando con las utilidades y la rentabilidad del negocio, más aún si la tendencia de las operaciones bancarias sean en su mayoría a través de los cajeros ATM, esto ocasionaría mayores costos de operación producto del incremento de personal para estos servicios que cuenta con segundo resguardo de valores a diferencia de un servicio normal que cuenta con solo un resguardo de valores. Hoy en día los tiempos han cambiado, la tecnología es distinta a la de hace 20 años, los controles y dispositivos de seguridad electrónica y satelital son más rigurosos y de mayor alcance, se cuenta con departamentos de Seguridad Electrónica y de Telecontrol que monitorean permanentemente las operaciones, las entidades privadas y públicas cuentan con mayores medidas de seguridad y nuestros clientes, las entidades bancarias evalúan con detenimiento los puntos de instalación de los cajeros ATM en coordinación con nuestro departamento de Seguridad. Esto hace suponer, que las operaciones han permanecido estáticas en el tiempo y mediante el rediseño y mejora de procesos, hemos propuesto la eliminación del segundo resguardo de valores sin vulnerar la seguridad de las operaciones y así optimizar los recursos de la compañía en este tipo de operaciones.