Media handling for conferencing in MANETs

Mobile Ad hoc NETworks (MANETs) are formed by devices set up temporarily to communicate without using a pre-existing network infrastructure. Devices in these networks are disparate in terms of resource capabilities (e.g. processing power, battery energy). Multihop Cellular Networks (MCNs) incorporate multihop mobile ad-hoc paradigms into 3G conventional single-hop cellular networks. Conferencing, an essential category of applications in MANETs and MCNs, includes popular applications such as audio/video conferencing. It is defined as an interactive multimedia service comprising online exchange of multimedia content among several users. Conferencing requires two sessions: a call signaling session and a media handling session. Call signaling is used to set up, modify, and tear down conference sessions. Media handling deals with aspects such as media transportation, media mixing, and transcoding. In this thesis, we are concerned with media handling for conferencing in MANETs and MCNs. We propose an architecture based on two overlay networks: one for mixing and one for control. The first overlay is composed of nodes acting as mixers. Each node in the network has a media connection with one mixer in the first overlay. A novel distributed mixing architecture that minimizes the number of mixers in end-to-end paths is proposed as an architectural solution for this first overlay. A sub-network of nodes, called controllers, composes the second overlay. Each controller controls a set of mixers, and collectively, they manage and control the two-overlay network. The management and control tasks are assured by a media signaling architecture based on an extended version of Megaco/H.L248. The two-overlay network is self-organizing, and thus automatically assigns users to mixers, controls mixers and controllers, and recovers the network from failures. We propose a novel self-organizing scheme that has three components: self-growing, self-shrinking and self-healing. Self-growing and self-shrinking use novel workload balancing schemes that make decisions to enable and disable mixers and controllers. The workload balancing schemes use resources efficiently by balancing the load among the nodes according to their capabilities. Self-healing detects failed nodes and recovers the network when failures of nodes with responsibilities (mixers and controllers) occur. Detection of failed nodes is based on a novel application-level failure detection architecture. A novel architecture for media handling in MCNs is proposed. We use mediator concepts to connect the media handling entities of a MANET with the media entities of a 3G cellular network. A media mediator assures signaling and media connectivity between the two networks and acts as a translator of the different media handling protocols

Behavioural Types for Local-First Software

Peer-to-peer systems are the most resilient form of distributed computing, but the design of robust protocols for their coordination is difficult. This makes it hard to specify and reason about global behaviour of such systems. This paper presents swarm protocols to specify such systems from a global viewpoint. Swarm protocols are projected to machines, that is local specifications of peers. We take inspiration from behavioural types with a key difference: peers communicate through an event notification mechanism rather than through point-to-point message passing. Our goal is to adhere to the principles of local-first software where network devices collaborate on a common task while retaining full autonomy: every participating device can locally make progress at all times, not encumbered by unavailability of other devices or network connections. This coordination-free approach leads to inconsistencies that may emerge during computations. Our main result shows that under suitable well-formedness conditions for swarm protocols consistency is eventually recovered and the locally observable behaviour of conforming machines will eventually match the global specification. Our model elaborates on the Actyx industrial platform and provides the basis for tool support: we sketch an implemented prototype which proves this work a viable step towards reasoning about local-first and peer-to-peer software systems

Multiparty/Multimedia Conferencing in Mobile Ad-Hoc Networks for Improving Communications between Firefighters

In current practice, firefighters’ communications systems are verbal, using a simplex Radio Frequency (RF) system (walkie-talkie). They use a push-to-talk mechanism in which only one person can talk at any time and all other firefighters will hear the messages. They use special codes (e.g. 1008, 1009, etc.) to express their current situation. Firefighters of the same team need to be in visual contact with each other at all times. This RF system does not support other functionalities (e.g. video communications, conference calls). In addition, because communication between firefighters is a flat structure, private communications is not possible. Mobile Ad-Hoc Networks (MANETs) are infrastructure-less and self-organized wireless networks of mobile devices, which are not based on any centralized control. MANETs are suitable for the hosting of a wide range of applications in emergency situations, such as natural or human-induced disasters, and military and commercial settings. Multimedia conferencing is an important category of application that can be deployed in MANETs. This includes well-known sets of applications, such as audio/video conferencing, data communications, and multiplayer games. Conferencing can be defined as the conversational exchange of data content between several parties. Conferencing requires, at the very least, the opening of two sessions: a call signaling session, and a media handling session. Call signaling is used to set up, modify, and terminate the conference. Media handling is used to cover the transportation of the media, and to control/manage the media mixers and media connections. So far, very little attention has been devoted to the firefighters’ communication system. In the present work, we focus on building a new communication system for firefighters using multimedia conferencing/sub-conferencing in MANETs. The background information for the firefighters’ current communications system and MANETs, along with the multimedia conferencing, is provided. The limitations of this system are determined, and the requirements are derived to determine the functionalities of a better communication system that will overcome current limitations. We have proposed a cluster-based signaling architecture that meets our requirements. We have also identified a state-of-the-art media handling and mixing system that meets most of our requirements, and have adapted it to inter-work with our signaling system. We have implemented the proposed architecture using SIP signaling protocol. Performance measurements have been performed on the prototype. Through experiments, we have found that the new multimedia communication system is a very promising approach to solve the current firefighters’ communication problems

Controlo do transporte de sessões multicast em redes dinâmicas

Mestrado em Engenharia Electrónica e TelecomunicaçõesHoje em dia assiste-se a um aumento considerável da procura de serviços ou aplicações para múltiplos utilizadores (multiparty), como streaming de conteúdos media, partilha de informações, colaboração entre utilizadores, entre outros. O suporte de tais serviços pela Internet mostra-se extremamente exigente para as actuais arquitecturas de rede, requerendo recursos e funcionalidades completamente fora do alcance de serem suportadas. Desta forma, é necessário investigar e desenvolver novos mecanismos que possibilitem simultaneamente um melhor e maior controlo a este nível. Neste âmbito, tem-se observado actualmente um aumento no número de arquitecturas propostas, capazes de integrar as vantagens do protocolo IP multicast na entrega e transporte de conteúdos multimédia a grupos de utilizadores. Por outro lado, a inclusão de informação de contexto da rede, ambiente e utilizadores proporciona uma maior personalização e adaptação nas decisões de controlo necessárias à rede. É neste sentido que o projecto C-Cast abordado nesta tese se enquadra, procurando especificar uma arquitectura capaz de integrar uma quantidade abrangente de informação de contexto por forma a fornecer personalização nas sessões de entrega de conteúdos multimédia. Para a gestão dos recursos de rede é também proposto um mecanismo de transporte dos conteúdos baseado em IP multicast, juntamente com a possibilidade de adaptação dos caminhos escolhidos na rede de core baseada na informação de contexto da rede e do utilizador. A junção destes factores visa então possibilitar uma melhor gestão dos recursos disponibilizados pela rede. O principal objectivo desta Tese é então focado no desenvolvimento de um módulo inteligente, capaz de permitir o transporte multiparty e reserva de recursos, permitindo a entrega dos conteúdos de uma forma personalizada e independente das capacidades da rede e do utilizador, melhorando não só a qualidade de serviço, como também a qualidade de experiência. De forma a implementar a proposta apresentada, recorreu-se à criação de um novo componente organizado segundo uma arquitectura interna hierarquizada e centralizada, na qual um único módulo (IPT Controller) central comanda vários outros módulos (IPT Node) distribuídos ao longo de toda a rede. Após concluída a implementação, provou-se que o componente é capaz de criar e remover várias reservas de recursos por forma a permitir o transporte multiparty por caminhos específicos na rede. Este mecanismo é também capaz de modificar reservas previamente efectuadas, permitindo que as sessões multimédia sejam capazes de responder às modificações de contexto na rede, actualizando possíveis sessões já existentes com um mínimo de interrupção de serviço possível para utilizadores que não tenham sofrido alterações. Avaliando os resultados obtidos, pode-se também concluir que o impacto do IPT na rede é ligeiro e menor em relação ao dos restantes componentes, pelo que não é um factor decisivo no desempenho global da arquitectura.Today we are witnessing a considerable increase in the demand for services or applications for multiple users (multiparty), such as streaming media content, information sharing, collaboration among users, among others. The support of such services over the Internet proves to be extremely demanding for the existing network architectures, requiring features and functionality completely out of reach of the current networks. Thus, investigation and development of new mechanisms that enable a superior management at this level is necessary. In this context, it is possible to observe an increase in the number of architectures proposed, which are able of integrating the advantages of the IP multicast protocol in the transport and delivery of multimedia content to user groups. Moreover, the inclusion of context information from the network, environment and users, provides a greater customization and adaptation in the decisions necessary to control the network. It in this context that the C-CAST project discussed in this dissertation is included, which tries to specify an architecture capable of integrating a comprehensive amount of context information in order to be able to provide superior dynamic sessions to deliver multimedia content. For the management of the network resources, it is also proposed a mechanism for the transport of multimedia content based on IP multicast. The possibility of path adaptation in the core network based on context information of both users and network is also considered. Is it with the combination of these factors that this project seeks to enable an improved management of the network’s resources. The main objective of this dissertation is then focused on the latter point of the C-CAST project architecture. It proposed the development of an intelligent module capable of allowing multiparty transport and resource reservation, enabling the delivery of multimedia content in a personalized way, independent of network and users capabilities, improving not only the quality of service, as well as quality of experience. In order to implement the proposed solution, a new component was developed, organized according to a hierarchical and centralized architecture in which a single central unit (IPT Controller) is able to command several other modules (IPT Node) deployed throughout the network. It was verified that the developed component is capable of creating and removing the necessary enforcements on the network to enable the multiparty transport through specific data paths. It is also capable of modifying previous enforcements, allowing the multimedia sessions to adapt themselves to context changes avoiding as much as possible to disrupt the existing services to users that were not subjected to modifications. Evaluating the obtained results, it is possible to conclude that the overall impact of the IPT component in the network is reduced and considerably less than the one of the remaining components. Hence, the IPT does not have a direct impact on the overall architecture performance

Application Layer Multicasting Overlay Protocol a NARADA Protocol

The conventional wisdom has been that Network Layer Internet protocol(IP) is the natural protocol layer for implementing multicast related functionality but it is still plagued with concerns pertaining to scalability, network management, deployment and support for higher layer functionality such as error, flow and congestion control. In this context, an alternative architecture is, Application layer multicast (End Systems Multicasting), where at Application layer, implements all multicast related functionality including membership management and packet replication. This shifting of multicast support from routers to end systems has the potential to address the most problems associated with IP multicast. In Application-layer multicast, applications arrange themselves as a logical overlay network and transfer data within the overlay network (between end hosts). In this context, we study these performance concerns in the context of the NARADA protocol (an application layer multicasting protocol). In Narada, end systems self-organize into an overlay structure using a fully distributed protocol. We present details of NARADA and evaluate it using NS-2 simulations. Our results indicate that the performance penalties are low both from the application and the network perspectives. We believe the potential benefits of transferring multicast functionality from routers to end systems, significantly outweigh the performance penalty incurred

Dagstuhl News January - December 2006

"Dagstuhl News" is a publication edited especially for the members of the Foundation "Informatikzentrum Schloss Dagstuhl" to thank them for their support. The News give a summary of the scientific work being done in Dagstuhl. Each Dagstuhl Seminar is presented by a small abstract describing the contents and scientific highlights of the seminar as well as the perspectives or challenges of the research topic