Actas JP2011 - Universidad de La Laguna

Actas XXII Jornadas de Paralelismo (JP2011) , La Laguna, Tenerife, 7-9 septiembre 2011Evaluating video streaming performance inMANETs using a testbedTim Bohrloch † , Carlos T. Calafate ‡ , Alvaro Torres ‡ , Juan-Carlos Cano ‡ , Pietro Manzoni ‡1Abstract— The complexity of evaluating video deliverystrategies in mobile ad-hoc networks (MANETs)has led most researchers to rely on simulation experimentsalone. However, in most cases, simulationsfail to replicate realistic conditions, and so the resultsobtained and the conclusions drawn from such resultsare not accurate. In this paper we describe a methodologythat allows evaluating the effectiveness of videocodecs in MANETs. Our methodology is based on awell-defined video quality evaluation framework thatconsiders different video codecs and transmission environments.We validate our methodology by comparingthe H.264/AVC and the MPEG-4/ASP videocodecs, showing that, in general, the former outperformsthe later in terms of video quality. For veryhigh loss rates, though, the differences between bothbecome minimal. We also show that the number ofhops between video transmitter and receiver is a decisivefactor affecting performance when the channelexperiences congestion. Moreover, in mobile scenarios,we find that the impact of congestion and routingdelay affects video streaming quality in different manners:while congestion is mainly responsible for randomlosses, routing delay is usually associated withlong loss bursts.Keywords— Video streaming; MANET; QoS;testbed; H.264 / AVC; MPEG-4 / ASP; ad-hocI. IntroductionVIDEO streaming in mobile ad-hoc networks(MANETs) is considered one of the most challengingresearch goals due to the combined effects ofwireless communications characteristics (multipathfading and shadowing, interferences, collisions, etc.)and topology maintenance in the presence of nodemobility, all of which negatively affect on-going videosessions. In particular, topology changes provokeintermittent connectivity, causing large packet lossbursts. Thus, assessing the effectiveness of videotransmission systems in ad-hoc networks is a relevantissue. In the past, most works addressing this issuehave resorted to simulation due to the complexity ofdeploying real testbeds. However, this approach doesnot allow for a thorough validation since results tendto be too optimistic. Additionally, the few works describingreal testbed experiments do not deal withthe IEEE 802.11e technology, which impedes offeringQoS support to video streams.In this work we introduce a methodology basedon emulation that allows evaluating video streamingperformance in real, 802.11e-based MANETs. Theproposed methodology relies on a video quality evaluationframework to assess the effectiveness of differentvideo codecs when transmitted over IP net-1† HfT Leipzig, Germanye-mail: Tim.Bohrloch@gmx.net‡ Universitat Politècnica de València, Spaine-mail: calafate@disca.upv.es, atcortes@batousay.com,{jucano, pmanzoni}@disca.upv.esworks. When focusing on MANET scenarios, wepropose performing an initial evaluation using a controlledpoint-to-point wireless channel to have a clearoverview of the video codec’s error resilience performance.Afterward, static multi-hop communicationscenarios are used to determine of impact of factorssuch as congestion and hop count on performance.Finally, we introduce mobile multi-hop communications,typical of MANET environments, to study theeffects of topology updating delays on the video qualityperceived by the user.To validate our methodology we assess the effectivenessof two well-known video coding standards -H.264/AVC [1] and MPEG-4 Part 2 [2] - followingthe proposed procedure. Experimental results showthat the H.264/AVC codec offers higher video qualityand, more important, they evidence how the differentsources of video data losses in MANETs impactthe video decoding process.This paper is organized as follows: in section IIwe present some related works, evidencing how ourwork differs from previous ones. In section III weintroduce the proposed video evaluation methodology.Section IV describes the video sequences usedfor testing, along with the experimental results obtainedin an emulated point-to-point channel whenvarying the loss rate. The results obtained in ourad-hoc network testbed are then presented in sectionV, comprising both static and mobile scenarios.Finally, section VI presents the main conclusions ofthis paper.II. Related worksIn the literature we can find works addressingvideo streaming performance in MANETs from differentperspectives.Schierl et al. [3] presented a scheme based on RaptorFEC that uses different sources for reliable mediastreaming in MANET scenarios with high route lossprobability. Their evaluation is based on ns-2 simulation.Sheltami [4] evaluates the performance of H.264protocol using two routing protocols: the Neighbor-Aware Clusterhead (NAC) and the Dynamic SourceRouting (DSR) protocols. The author shows thatit is feasible to have video over MANETs within anaverage distance of 6 hops, and requiring 5.5 Mbpson average.Calafate et al. [5] propose a QoS frameworkfor MANETs combining IEEE 802.11e technology, amultipath routing algorithm, and a distributed admissioncontrol algorithm. Their solution was testedvia simulation, and Peak Signal-to-Noise Ratio re-JP2011-385