Déploiement à grande échelle de la voix sur IP dans des environnements hétérogènes. (Large scale VoIP deployment over heterogeneous environments)

In this thesis, we focus on large scale Voice over IP (VoIP) deployment over heterogeneous Internet environments. We first present an overview of VoIP coding and transmission mechanisms. Then, we investigate performance limitations in the case of a large number of VoIP flows transported over wired Internet links between peer VoIP gateways. We address, in the first part of the thesis, the need to design congestion control for the growing class of VoIP traffic and we propose a novel VoIP congestion control scheme. This scheme combines RTP voice flow multiplexing and the TCP-friendly congestion control mechanism in order to improve VoIP transmission efficiency and performance while being fair with coexisting Internet traffic. The second part of this thesis deals with VoIP transmission over IEEE 802.11e wireless LAN environments (WLAN). We develop an analytical model to evaluate the capacity of an 802.11e network in terms of VoIP communications while conditioning on the used audio codec and MAC/PHY parameters. This model can be applied to tune IEEE 802.11e standard parameters in order to increase the WLAN capacity while considering stringent requirements of interactive VoIP communications. In the last part of this thesis we study the case of VoIP transmission over heterogeneous Internet environments where WLAN represents the lasthop Internet access link. We propose an architecture that is based on a VoIP gateway located at the edge of the wired and the wireless network, and used to adapt voice flows according to wireless network characteristics. The proposed adaptation mechanism dynamically estimates wireless channel congestion state and allows the differentiation between congestion loss and loss caused by wireless channel transmission errors. Then, the appropriate adaptation is applied. Specifically, in our proposed adaptive mechanism, the medium-access control (MAC) protocol at the wireless end stations does not need to be modified, making the mechanism more readily deployable over the existing network infrastructure.