Joint Adoption of QoS Schemes for MPEG Streams Artur Ziviani (ziviani@lncc.br) National Laboratory for Scientiﬁc Computing (LNCC) - Brazil Bernd E. Wolﬁnger (wolfinger@informatik.uni-hamburg.de) CS Dept. / TKRN - Hamburg University - Germany Jos´ e F. de Rezende (rezende@gta.ufrj.br) GTA/COPPE/Poli - Federal University of Rio de Janeiro - Brazil Otto Carlos M. B. Duarte (otto@gta.ufrj.br) GTA/COPPE/Poli - Federal University of Rio de Janeiro - Brazil Serge Fdida (serge.fdida@lip6.fr) LIP6 - Universit´ e Pierre et Marie Curie (Paris 6) - France Abstract. Indiscriminated packet discards strongly degrade the quality perceived by end users of MPEG video transmissions. This paper investigates diﬀerent Quality of Service (QoS) schemes and the tradeoﬀs of jointly adopting such schemes to improve the delivery quality of an MPEG stream. From an analytical model, we evaluate the impact of frame losses on the quality of MPEG streams and on the waste of network resources. Our assessment considers issues such as the use of redundancy by applying a Forward Error Correction (FEC) scheme to tolerate losses, the changing of the compression factor in MPEG encoding, the unequal protection of MPEG frames in a Diﬀerentiated Services environment, and how to evaluate the impact of network losses onto application quality. Results provide predicted bounds on the quality to be expected by end users as well as guidelines on how to take the best advantage from the joint adoption of the investigated QoS schemes. Keywords: Quality of Service, Video Communications, MPEG, Diﬀerentiated Ser- vices, Forward Error Correction. 1. Introduction The best-eﬀort model of the traditional Internet has become inade- quate to deal with the very diverse requirements on network Quality of Service (QoS) of an ever-increasing range of traﬃc types [34]. A key point for the success of the new multimedia applications is the network QoS provided to video and audio streams [25, 33, 36, 35]. To address the issue of providing a QoS support for the transmission of ﬂows from applications with diﬀerent QoS requirements, diﬀerent approaches are currently being developed, such as adaptive applications [12, 11, 18], QoS-based routing [8, 7], and the Diﬀerentiated Services (DiﬀServ) c  2004 Kluwer Academic Publishers. Printed in the Netherlands. ZWRDF-mta-final.tex; 18/11/2004; 13:53; p.1