Département Réseau, Sécurité et Multimédia Rapport d'Activités 2008

Media and NetworksIP-based transmission of real-time services over wireless linksResearch Staff : Loutfi Nuaymi, Xavier Lagrange, Kevin Perros – Ph.D. Students : Neila El Héni,Elizabeth Martinez FernandezKeywords : UMTS, Header compressions, ROHCApplications : Real-time services, Video streaming, VoIPPartners & Funding : TELECOM Bretagne (RSM), FT R&D (project leader), Thales Communications,IRISA, Alcatel and Eurecom. Funded by French Government RNRT as COSINUS ProjectIntroductionCellular and Wireless networks provide bothnon real time and real time services (Voice,video). For the latter the quality of service isan important issue. In UMTS real time servicesare generally based on a circuit-switchedapproach. However as IP-based solutions willbe generalized in a near future it is necessaryto study real-time services over IP.COSINUS (COmmunications de Servicestemps-réel / IP dans uN réseaU Sans fil) is anRNRT (Réseau National de Recherche enTélécommunications) project. The main topicis the study of IPv6-based real time services,both audio and video, over third-generationcellular network, UMTS and over WLAN(Wireless Local Area Network) 802.11/WiFi. Inparticular, the received quality will beobserved, controlled, and improved thanks tothe use of adequate protection means, theimprovement in multimedia codec robustnessand the integration of new mechanisms suchas header compression. The specific nature ofthe radio link is taken into account. The use ofthe frequency spectrum is a major constraintin the optimization of the transmission over thewireless link. The transmission servicesconsidered in COSINUS are conversational IPservices (e. g., phone, visiophony) and differedreal-time IP services (e.g., audio and videostreaming). In a period where these servicesare often mentioned as highly promising andwhere some of them are already proposed tothe public by operators, there is a lack ofstudies and results on this subject.RealizationTransmission on the UMTS radio interface isbased on the concept of RAB: Radio AccessBearer. A RAB mainly includes the definition ofthe channel coding and a set of possible datablock sizes. The possible error correcting codesare specified in the 3GPP recommendationsbut nothing is said about the RAB format for agiven service.The first part of the work investigated theUMTS RAB configurations for VoIMS (VoIP overIP Multimedia Sub-system) used in the 3GUMTS System. This has been done with afocus on the ROHC header compressionimpacts, different RAB multiplexingmethodologies, rate matching algorithms andother UMTS radio protocols [2].The quality of service is analyzed within theproject with a real-time platform built on thebasis of the Rhodos UMTS testbed developpedby Eurecom [1]. TELECOM Bretagne is incharge of integrating the ROHC mechanism inthat testbed. This integration was completed in2007. Several hardware and system problemswere solved before a stable new ROHCincludingUMTS Platform was obtained. Thisnew platform was used for UMTS voice andvideo transmissions to evaluate theperformance of the ROHC mechanism. TheTELECOM Bretagne part of COSINUS wasconcluded in Sept 2007. COSINUS projectended completely in the beginning of 2008.Future WorkNow that COSINUS has ended, investigationsare done for new research studies about ROHCand UMTS. The platform obtained in COSINUSwill be very useful for this kind of research.References[1] M Wetterwald et al., “A UMTS TDDsoftware radio platform”, in ReconfigurableMobile Radio Systems, G. Vivier (editors),2007, ISTE, ISBN 9781905209460.[2] N. El Héni, B. Badard, V. Diascorn, L.Nuaymi, "Performance of RAB mapping andROHC for the support of VoIP over UMTS, "18th annual IEEE international symposium onpersonal, indoor and mobile radiocommunications PIMRC'07, September 3-7,Athens, Greece, 200714 Extract of Pracom’s Annual Report 2008