Evaluering af rutnings pålidelighed i mobile ad hoc netværk ved brug af topologi emulator

Evaluation of Routing Dependability in MANETs using a Topology Emulator

N. Jensen, Morten ; Nickelsen, Anders

10. term

Elektronik og IT, Kandidatuddannelsen (Spec. Distribuerede Systemer)

2007

152

Forsøg med trådløse netværk kan give meget forskellige resultater, fordi radiomiljøet er uforudsigeligt. For at håndtere dette udvikler og udruller specialet et testmiljø til topologiemulering, der skal vurdere routingens pålidelighed i mobile ad hoc-netværk (MANET). Use casen er en meget pålidelig videokonference, der skal give lægelig assistance fra et hospital til en kørende ambulance. Det kræver ad hoc-routing over flere hop fra ambulancen til en gateway i ad hoc-netværket. Topologiemulatoren lægger egenskaberne fra trådløse forbindelser oven på kablede forbindelser mellem slutnoder. Den bruger detaljerede modeller for tab og forsinkelse, som afspejler WLAN 802.11a med et OFDM-fysisk lag samt statistiske fading-modeller for radiokanalen. Funktionelle og ydelsesmæssige krav til testmiljøet er afledt og testmiljøet er implementeret og verificeret op imod disse krav. Der er defineret en ramme for routevaluering med krav til ydeevne og pålidelighed, baseret på use casen. Inden for denne ramme er DSR og OLSR evalueret som repræsentanter for henholdsvis reaktiv (finder ruter ved behov) og proaktiv (vedligeholder ruter løbende) ad hoc-routing. Resultaterne peger på, at den reaktive DSR er et bedre valg i meget dynamiske ad hoc-scenarier, fordi dens ende-til-ende-pålidelighed er højere end OLSR’s. Der er dog behov for mere systematisk evaluering af de påvirkende faktorer i mobile miljøer for yderligere at underbygge denne konklusion.

Experiments on wireless networks can vary widely because the radio environment is unpredictable. To address this, the thesis develops and deploys a topology emulation testbed to evaluate routing dependability in mobile ad hoc networks (MANETs). The use case is a highly dependable video conferencing application that provides medical assistance from a hospital to a moving ambulance. This requires ad hoc multi-hop routing from the ambulance to a gateway in the ad hoc network. The topology emulator maps the behavior of wireless links onto wired connections between end nodes. It uses detailed models of loss and delay that reflect WLAN 802.11a with an OFDM physical layer and statistical channel fading. Functional and performance requirements for the testbed were derived, and the testbed was implemented and verified against these requirements. A routing evaluation framework with performance and dependability requirements, based on the use case, was defined. Within this framework, DSR and OLSR were evaluated as representatives of reactive (on-demand) and proactive (continuously maintained) ad hoc routing, respectively. The results indicate that the reactive DSR is a better choice for highly dynamic ad hoc scenarios, as its end-to-end reliability surpasses that of OLSR. However, more systematic evaluation of factors in mobile environments is needed to further substantiate this conclusion.

[This abstract was generated with the help of AI]

routing ; emulation ; dependability ; manets

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