Voice packet delay evaluation in an IP network using voice stream multiplexing scheme

Orientador: Shusaburo MotoyamaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de ComputaçãoResumo: Neste estudo são avaliados o desempenho e o impacto do tráfego de voz em uma rede IP. Na rede IP o sinal de voz é transmitido através de pacotes que são identificados por um conjunto de cabeçalhos. Cada pacote de voz tem a carga útil, composta por um quadro (frame) de voz, muito menor que a carga útil de um pacote de dados. Desta forma, a rede IP pode tornar-se pouco eficiente para transportar sinal de voz. Além disso, o serviço de voz requer também interatividade o que implica em realocar, através de mecanismos apropriados, os recursos da rede IP. Uma das técnicas que pode ser usada é a aplicação de política de priorização do tráfego de voz que em contrapartida pode degradar o desempenho de tráfego com prioridade menor. A previsão de tráfego de voz crescente na rede IP pode torná-la bastante ineficiente, além de degradar o desempenho do tráfego de dados. Para minimizar este problema o esquema de multiplexagem dos quadros de voz pode ser usado. Um modelo matemático é proposto neste estudo para analisar o impacto do tráfego do pacote de voz em uma rede IP. O estudo é conduzido considerando-se sem e com a aplicação de multiplexagem de quadros de voz nos pacotes de voz e o parâmetro de desempenho é o atraso de cada pacote na rede IP. Em seguida, um outro modelo mais complexo, com fontes de voz ON-OFF e de dados do tipo HTTP, é simulado no ambiente do MatLab/SimEvent para o mesmo cenário estudado no modelo analítico. Os resultados obtidos mostraram que o comportamento da rede IP é similar tanto no modelo analítico como no modelo simulado e que a técnica de multiplexagem dos quadros de voz é um esquema eficiente para economizar a largura de banda de um enlace da rede IP.Abstract: In this study, the performance and impact of voice traffic in an IP network are evaluated. In the IP network, the voice signal is transmitted through packets that are identified by a set of headers. Each voice packet has payload composed of one voice frame, which is smaller than the payload of data packet. In this way, the IP network may become ineffective to carry the voice signal. Furthermore, the voice service also requires interactivity which means the need for reallocation, through appropriate mechanisms, the resources of the IP network. One of the techniques may be used is through the adoption of voice traffic priority policy which on other hand it may degrade the performance of data traffic with lower priority. The expected fast growing of voice traffic in IP network can make it inefficient as well as to degrade the data traffic performance. To minimize this problem the voice stream multiplexing scheme can be used. A mathematical model is proposed in this study to examine the impact of voice packet traffic in an IP network. The study is carried out considering with and without the application of voice frame multiplexing and the performance parameter is the delay of each packet in the IP network. Then, a more complex model, with ONOFF voice sources and data sources of HTTP type, is simulated in MatLab/SimEvent environment for the same scenario used in analytical model. The obtained results showed that the IP network behavior is similar in both analytical and simulated models and that voice frame multiplexing technique is an efficient scheme to save the bandwidth of a link.MestradoTelecomunicações e TelemáticaMestre em Engenharia Elétric

Mixed-species aggregations in arthropods

This review offers the first synthesis of the research on mixed-species groupings of arthropods and highlights the behavioural and evolutionary questions raised by such behaviour. Mixed-species groups are commonly found in mammals and birds. Such groups are also observed in a large range of arthropod taxa independent of their level of sociality. Several examples are presented to highlight the mechanisms underlying such groupings, particularly the evidence for phylogenetic proximity between members that promotes cross-species recognition. The advantages offered by such aggregates are described and discussed. These advantages can be attributed to the increase in group size and could be identical to those of non-mixed groupings, but competition-cooperation dynamics might also be involved, and such effects may differ between homo- and heterospecific groups. We discuss three extreme cases of interspecific recognition that are likely involved in mixed-species groups as vectors for cross-species aggregation: tolerance behaviour between two social species, one-way mechanism in which one species is attractive to others and two-way mechanism of mutual attraction. As shown in this review, the study of mixed-species groups offers biologists an interesting way to explore the frontiers of cooperation-competition, including the process of sympatric speciation.PostprintPeer reviewe

The Sense of Smell in Ants

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