Bart Duysburgh

On the influence of best-effort network conditions on the perceived speech quality of VoIP connections

When voice traffic is transported over a packet-based network, a number of conditions different from the ones in the traditional circuit-switched network will have an influence on the quality of the speech signal as perceived by the users. In particular, distortion of the voice signal due to delay jitter and partial loss of signal caused by packet loss will have an important impact. Therefore, in order to determine the influence of delay jitter and packet loss on the perceived quality, an objective speech quality assessment system, called DSLA, is used to predict the mean opinion score for voice connections, which are set up on a test-bed, subject to artificially introduced network conditions. A decomposition of the voice degradation is made into different parts, due to sampling, digitization, encoding/decoding, packet loss and delay jitter, respectively. It is found that delay jitter has a devastating influence on the perceived quality, when no dejittering buffer is used. However, when the received signal is dejittered, the degradation due to jitter is similar to the one caused by packet loss.

An active networking based service for media transcoding in multicast sessions

Active networking is one of the suggested technologies to introduce additional intelligence and programmability in the network and its services. In this paper, the use of active networking to support advanced multicast services providing media transcoding inside the network is investigated. In the multicast service different versions of the streamed data are made available and customers can select a specific version according to their wishes or their capabilities. Based on the active networking facilities of the underlying framework the different versions of the streamed data can be created inside the network, through transformations or transcodings of the original data. Both design and performance issues of the detailed service are discussed. A new multicast tree set-up protocol, taking into account the required transcodings, is introduced. A number of different strategies are discussed optimizing the location of the transcodings as well as the use of bandwidth in the network, while considering the availability of sufficient processing power in the nodes. The performance analysis is done for a voice stream multicast service, addressing the efficiency of the tree set-up strategies, the optimization of network resource utilization, the use of processing power for transcodings, and the resulting quality of streamed voice signals after multiple transcodings.

Optimizing multimedia transcoding multicast trees

In this paper, network hosted transcoding is studied for the optimization of resources in multicast applications. The configuration is as follows: one source node is sending a signal (e.g. a video stream) and several destinations request that signal but at a bit rate adjusted to their access link. Instead of transcoding at the source node, the nodes inside the network will take care of the reduction in bit rate. The advantages are that the source load and overall bandwidth usage are reduced while end-users get the service at a customized quality. The focus of this paper is on the calculation of the optimal multicast tree, including transcoding location optimization and estimation of the resource usage gain.

Data Transcoding in Multicast Sessions in Active Networks

In this paper a multicast application is presented, based on active networking techniques, in which processing of the multicasted data is done in intermediate network nodes, according to requests or demands done by users joining the multicast session. The problem of transcoding in multicast sessions is divided into two subproblems. First some issues about the application of active networking techniques are briefly discussed. Then, the problem concerning the optimisation of the location of transcoding nodes in the multicast tree will be the main subject of this paper. The exact solution and a number of heuristics are discussed and simulations of the solutions will illustrate the advantages of the application of transcoding in multicast sessions.

Design and analysis of a stable set-up protocol for transcoding multicast trees in active networks

Based on active networking, an advanced streaming service was designed to offer different formats of the same stream using a single multicast tree. To that end, the initial format of the stream that is sent into the tree is transcoded to the other requested formats in the nodes of the tree, based on application level functionality residing in these network nodes. To set up such a multicast tree (including the necessary forwarding state in the nodes) and to install the necessary functionality in the nodes, a number of tree set-up procedures were designed. In this paper, performance aspects of these procedures are investigated: the stability and consistency of the forwarding state during the set-up procedures and the influence of dynamic user behaviour on the multicast tree. This performance assessment is based on a thorough analysis of the different set-up procedures and on simulations of the procedures. Based on the analysis, it is seen that great care must be taken during the set-up procedures in order to avoid interference with the existing streams. Therefore, extensions for the procedures are proposed. Furthermore, the influence of dynamic user behaviour on session state and performance attributes is analysed.

On the quality and performance of active networking based media transcoding in multicast sessions

In this paper an advanced network service is described, which enables customisation of data services and adds extra flexibility to the networks data transporting capabilities. More specifically, a multicast service providing media transcoding inside the network is detailed. Whereas in traditional multicast services only one specific version of the data is available, in this service customers can choose from a range of different versions of the data. Customers can select a specific version according to their own wishes or to the capabilities of their connection and terminal. Based on active networking concepts, the different versions of the streamed data are created inside the network, by performing transformations of the original data in the network nodes. As a consequence, server load can be reduced and bandwidth usage in the multicast tree can be optimised. After the introduction of the multicast tree set-up strategies for this service, the focus of the discussion will be on performance aspects and on the resulting quality. In this discussion, a voice streaming service is considered, providing different encodings of the voice data.