Distribuição eficiente de IPTV

Mestrado em Engenharia Electrónica e TelecomunicaçõesAs redes de transporte de telecomunica c~oes foram inicialmente concebidas para transportar chamadas telef onicas atrav es de tecnologias baseadas em comuta c~ao de circuitos. A adapta c~ao destas redes para transportar tr afego de dados apresenta ine ci^encias que contribuem para que as receitas geradas pelos operadores n~ao acompanhem a largura de banda fornecida aos clientes. Este facto tem vindo agravar-se com o crescimento de servi cos como o IPTV, servi co que requer elevada largura de banda, varia c~ao acentuada da taxa de transmiss~ao e liga c~oes ponto-multiponto. A tecnologia Ethernet surge como ponto de partida (e chegada, pois mais de 95% do tr afego de dados e gerado ou tem como destino uma porta Ethernet [1]) para novas tecnologias de rede de transporte, chamadas tecnologias Carrier Ethernet. Neste documento e estudada a tecnologia Ethernet, os requisitos de uma tecnologia Carrier Ethernet e a promissora tecnologia MPLS-TP, ainda em processo de normaliza c~ao. Com o prop osito de otimizar a distribui c~ao do servi co IPTV e proposto um cen ario, onde se veri ca que o recurso a transmiss~ao combinada de canais unicast e multicast pode resultar num uso mais e ciente dos recursos da rede.The telecommunication aggregation networks were initially designed to transport phone calls, using technologies based on circuit switching. The adaptation of those networks to transport data trafic has some ineficiencies, which results, that the operator`s revenues do not follow the bandwidth provided to customers. This fact has become a growing problem with the development of services such as IPTV, a service which requires high bandwidth, high transmission rate variation and point-multipoint connections. The Ethernet appears as a starting point (and ending as well, since more than 95 % of the data tra c is generated or is destinated to an Ethernet port [1]) for new aggregation network's technologies, called Carrier Ethernet technologies. This paper, presents a study of the Ethernet technology, requirements for Carrier Ethernet technologies and the promising MPLS-TP, still in the standardization process. In order to optimize IPTV service distribution, there is proposed a scenario, where it was verified that the combined use of unicast and multicast transmission can result in an eficient use of network resources

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved