Actas JP2011 - Universidad de La Laguna

Actas XXII Jornadas de Paralelismo (JP2011) , La Laguna, Tenerife, 7-9 septiembre 2011RouterRNCUMTSServerWiMAX(1)Wi-Fi(1)Wi-Fi(2)WiMAX(2)Wi-Fi(3)User EquipmentFig. 5.VHO scheme.1000UMTS WiMAX Wi-FiWireless TechnologiesUMTSWiMAXWi-FiLatency per packet (ms)1001010 200 400 600 800 1000 1200Time (s)Fig. 7. Wireless technologies usage.0.10 200 400 600 800 1000 1200Time (s)Fig. 9. Wireless technologies latency.Throughput (kbps)30000250002000015000100005000UMTS WiMAX Wi-Fi00 200 400 600 800 1000 1200Fig. 8.Time (s)Wireless technologies throughput.LINK DOWN events, we can observe that latenciesreached by the latter processes are between 0.04 and0.11 milliseconds. The difference among these latenciesis due to the number of processes performed,as mentioned before. Concerning packet loss, TableII also presents the number of packets that havenot been delivered while the VHO process was beingperformed. The amount of undelivered data isrelated to the bandwidth available at the new network.As shown in the referred table, VHO processesthat switch from a network with higher bandwidth toa network with lower bandwidth experience a higheramount of packet losses.The results were obtained under “best-case” conditions,since there are no other user equipmentsrequesting services or decreasing the performanceof the available networks. Therefore, the resultingmean values of the different metrics measured mustbe considered as optimistic results, in order to avoidany erroneous conclusion.VII. ConclusionsIn this paper we have performed several experimentsin order to evaluate a technology-aware VHDAwhich considers availability and capacity of the networkfor the decision making process. The frameworkused for experimentation is based on the NetworkSimulator (ns-2), allowing us to evaluate theVHO process under the IEEE 802.21 standard.Experiments showed that VHO processes reachhigher latencies when dealing with newly discoveredcandidate networks due to the processes triggeredin order to perform a seamless VHO. Concerningpacket loss, VHO processes drop packets due to therestriction of bandwidth availability whenever downgradingfrom a network to another. Results were optimisticdue to the “best-case” conditions offered bythe different wireless technologies, since at the scenariono other traffic was decreasing the performanceof each network.We conclude that different improvements canbe suggested to outperform the current evaluatedVHDA whenever the conditions differ from thoseconsidered in this paper. In particular, high degreesof congestion, as well as other parameters (user preferences,mobile capabilities, etc.), will require a moreJP2011-431