Département Réseau, Sécurité et Multimédia Rapport d'Activités 2008

Optimized mobility management in heterogeneous accessnetworksResearch Staff : Nicolas Montavont, Jean-Marie Bonnin, Xavier LagrangePh.D. student: Richard RouilKeywords : heterogeneous access networks, seamless mobility, IEEE 802.21, wireless networksimulation, NS-2Applications : ITS, transportation systemPartners & Funding : NIST (National Institute of Standards and Technology, USA)IntroductionRealizationThe main objective of this project is the designand the simulation of a unified framework tomanage handover across heterogeneousenvironment. The target scenario is themanagement of multiple mobile nodes thataccess the Internet through variouscommunication technologies. In this context, itis important for mobile nodes to learn theenvironment characteristics to help flowdistribution over available networkattachments. In this learning process, we needto focus on the delay of handover in order tomake mobility as seamless as possible. Inorder to faster the flow redirection acrossvarious interfaces, we will then develop stronginteraction between layers.In addition to the environment discovery, aninformation exchange mechanism among thedifferent nodes in the system need to bedeveloped in order to enhance the globalknowledge of the network topology on eachnode. This work is then tied to standardizationeffort of IEEE 802.21 that designs mechanismsto enable handover and interoperabilitybetween heterogeneous network typesincluding both 802 and non 802 networks.The second major topic of this project is thesimulation framework. Research intelecommunication has always relied onsimulation for evaluation purpose. Would it befor deployment of wireless base stations or forthe investigation of corner cases of a particularprotocol, the simulation tool brings animportant evaluation framework to a validationprocess. It is a complementary study ofanalysis performance and it allows focusing ona set of parameters to adjust the specificationof a protocol. In this project several scenariosare simulated to investigate all aspects ofmobility.A new IEEE 802.16 model has been designedfor the network simulator NS-2 [1]. Thissimulation framework has been adopted by theWiMAX forum as the official IEEE 802.16simulation model. It provides the MAC andPHY layers on both Base Station and MobileStation. We also proposed a set of schedulingalgorithms for the base stations to control slotallocation in the WiMAX system [2].Lately, we focus on the MIH messagetransport. In the standard, the actual transportmechanism is not specified but the MIHmessages can be carried over layer 2, layer 3,or any layer above. The low packet latencyand reliability dictate the selection of thetransport protocol. If the necessary signaling isnot completed prior to losing connectivity, themobile node relies solely on local informationand may connect to an invalid network. Themain reason to trigger a handover is adegredation in signal quality. This also meansthat the connection is suffering from higherpacket loss rate. Thus the transport protocolcarrying the MIH messages must be able tomaintain its service under conditions of highpacket loss rate. Traditional transportprotocols, namely User Datagram Protocol(UDP) and Transmission Control Protocol (TCP)provide communication between two InternetProtocol (IP) addresses and rely on additionalmechanisms such as Mobile IP to handlemobility. This means that the performance ofthese protocols is dependant on the mobilityprotocol located at the network layer. Incontrast, Stream Control Transport Protocol(SCTP) embeds multihoming andmultistreaming capabilities. The DynamicAddress Reconfiguration also allows SCTP toperform layer 4 handovers. Thus we arestudying the advantages and performances ofthese transport protocols in order to provide acomprehensive analysis. This analysis hasbeen presented at the IETF, in the MIPSHOP26 Extract of Pracom’s Annual Report 2008