Resumo em Inglês:

Different multicast routing protocols construct their distribution trees based on the information obtained from the unicast routing infrastructure. Nevertheless, the design of most of these protocols do not take into account that unicast routes may be asymmetric. Indeed, unicast routes in the Internet are very asymmetric. The effects on the quality of the multicast trees vary according to the routing protocol. These are particularly important for protocols that use the recursive unicast approach to allow the progressive deployment of the multicast service. This paper analyses the effects of asymmetric unicast routing on different multicast protocols. We concentrate on two approaches that implement the multicast service trough recursive unicast trees, HBH (Hop-By-Hop multicast routing protocol) and REUNITE (Recursive UNIcast TrEes). Both protocols construct source-specific trees exclusively, which simplify address allocation. As data packets have unicast destination addresses, pure unicast routers are transparently supported. The branching-nodes recursively create packet copies to implement the distribution. Nevertheless, the tree construction algorithms implemented by HBH and REUNITE are different. The design of HBH takes into account the unicast routing asymmetries of the network. HBH is able to always construct a Shortest-Path Tree. Consequently, HBH provides shorter delay routes in asymmetric networks, and provides smaller bandwidth consumption because useless data duplication is avoided. The results obtained from simulation show the effects of unicast routing asymmetries in the different multicast protocols.

Resumo em Inglês:

Deering's model of Internet group communication, in spite of its simplicity and elegance, imposes limits on the complete development of IP multicast, due either to the profusion of contradictory requirements of applications, or to the reduced support provided by the network core for technical or economic reasons. Even if some of these difficulties may be resolved at the transport or application layers, thus remaining outside the scope of the present model, there also appear defects within this model, mainly due to inter-domain routing, involving address management, to QoS insensitivity and to loss of functionality. The recognition of these defects has already led to the solution presented by the MASC/BGMP project, which involves a transition from the present model. However there are many who argue that the success of unicast applications in TCP/IP will only be repeated in multicast applications through the use of much simpler solutions than the existing ones, or by including greater intelligence in the network interior. With this in mind, we analyse here the proposals RAMA and XCAST, which may be seen to demonstrate greater simplicity. We also look at AIM, designed for organising receivers into subgroups with similar interests. Leveraging Internet group applications will certainly involve one or other, or even both, of these approaches.

Resumo em Inglês:

A critical problem faced by feedback-merger mechanisms is the lack of information that is discarded due to the hidden nodes in multicast trees. A node is said to be hidden from another if it is located in a sub tree that is a result from a fork in any upstream node. We propose in this paper the virtual layering scheme to avoid the problem caused by hidden-nodes in multi-layered multicast video environments. The virtual layering scheme induces intermediate nodes to keep extra states of the multicast session, which reduces the video degradation for the whole set of receivers. Furthermore, this scheme is coupled with the Direct Algorithm in order to improve the degree of satisfaction at heterogeneous receivers. The algorithm relies on a mechanism that dynamically controls the rates of the video layers and addresses scalability issues by implementing a merging procedure at intermediate nodes in order to avoid packet implosion at the source. The Virtual Layering scheme combined with the Direct Algorithm is optimized to achieve high global video quality and reduced bandwidth requirements. The results show that the proposed scheme leads to improved global video quality at heterogeneous receivers with no cost of extra bandwidth.

Resumo em Inglês:

Multimedia networks will support a wide range of applications with different requirements and traffic characteristics. Connection Admission Control (CAC) algorithms are used to decide whether an incoming connection should be accepted or rejected in order to maintain the quality of service (QoS) demanded by the applications. The objective of this work is to present an environment we developed useful for performance analysis, measurements and experimentation, in particular for testing resource usage based on different traffic characteristics. We demonstrate how a study of the effectiveness of different CAC algorithms can be performed from measurements collected using an ATM switch and the tools we developed. For the studies we selected and implemented two CAC algorithms, one for a non-regulated traffic, proposed by [14], and other for a leaky-bucket regulated traffic, proposed by [5]. The environment tools include a traffic generator supporting IP and native-ATM as well as a CAC module that implements the algorithms above and can be used in conjunction with our test environment. These tools are currently part of the Tangram-II modeling environment [3,11] and available to download.

Resumo em Inglês:

This paper presents a framework for the creation of transport protocols for mobile hosts that use multiple link layers simultaneously for the same connection. This abstraction provides an end-to-end transport layer channel between two applications that do not have to be aware of host mobility. The channel is composed of multiple network layer sub-channels. A sub-channel is an end-to-end network layer connection that is mapped to one physical interface. Inverse multiplexing is used at the transport level to divide application data into sub-channels, and a rate-based transmission mechanism provides congestion avoidance. The same mechanism is used to differentiate transmission losses from congestion losses, resulting in good throughput in lossy wireless links. Experimental results for two protocols created using this framework validate our design choices.

Resumo em Inglês:

In distributed applications based on mobile agents, coordination and synchronization of the actions executed by a team of mobile agents are difficult tasks. The main difficulty comes from the fact that coordination requires the agents to interact with each other in spite of their dynamically changing locations. In this paper we present a mechanism for coordinating mobile agents which handles the problem of locating and addressing members in a group of mobile agents. This mechanism, which we called Broadcast Channel, implements reliable broadcasts of messages to a group of mobile agents, independently of their current locations.

Resumo em Inglês:

This paper proposes an architecture for distributed management of high-layer protocols and network services. Based on the IETF Script MIB, the Trace architecture provides mechanisms for the delegation of management tasks to mid-level managers (MLMs), which interact with monitoring and action agents to have them executed. The paper introduces PTSL (Protocol Trace Specification Language), a graphical/textual language created to allow network managers to specify protocol traces. The specifications are used by mid-level managers to program the monitoring agents. Once programmed, these agents start to monitor the occurrence of the traces. The information obtained is analyzed by the mid-level managers, which may ask action agents for the execution of procedures (e.g. Perl scripts), making the automation of several management tasks possible.