VoIP over DVB-RCS satellite systems: Trial results and the impact of adaptive speech coding using cross-layer design

VoIP is one of the most popular applications on the Internet. The DVB-S2 (digital video broadcasting-satellite version 2) and DVB-RCS (digital video broadcasting-return channel satellite) standards provide the potential for reliable and efficient voice and data transfer over satellite networks. This is important, as satellites can play a role in broadband service provision by addressing the cases of limited terrestrial access such as in rural or underserved areas. The first part of this paper presents the results of our VoIP trials with different commercial DVB-S/RCS satellite offers and popular internet telephony and videoconferencing applications (Skype, MSN, etc.). These results reveal that packet delay and jitter are strongly affected by the satellite network component as well as the type of speech codec used. Accordingly, research presented in the second part of this paper is focused on dynamic speech coding rate control adapted to the conditions of the underlying network, in which the satellite domain presents the most challenging portion of the end-to-end path. For this purpose, a novel cross-layer mechanism is proposed to facilitate and increase the accuracy of the speech coding rate adaptation mechanism. Cross-layer design is a relatively new idea aiming to exploit information exchange among layers of the protocol stack. Our simulation analyses show that the proposed cross-layer mechanism can help us in optimally adjusting the speech coding rate to maintain the user-perceived quality in terms of MOS (mean opinion score) in the face of time-varying available satellite channel capacity.