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Characteristics of QoS-Guaranteed TCP on Real Mobile Terminal in Wireless LAN

Characteristics of QoS-Guaranteed TCP on Real Mobile Terminal in Wireless LAN. Remi Ando † Tutomu Murase ‡ Masato Oguchi † † Ochanomizu University,Japan ‡ NEC Corporation. Outline. Background QoS-TCP Unfairness problem of TCP throughput on Wireless LAN Characteristics of AP

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Characteristics of QoS-Guaranteed TCP on Real Mobile Terminal in Wireless LAN

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  1. Characteristics of QoS-Guaranteed TCP on Real Mobile Terminal in Wireless LAN Remi Ando† TutomuMurase‡ Masato Oguchi† †OchanomizuUniversity,Japan ‡ NEC Corporation

  2. Outline • Background • QoS-TCP • Unfairness problem of TCP throughput on Wireless LAN • Characteristics of AP • Buffer sizes of APs • Previous Researches about QoS-TCP • Problem and experiment on QoS control • Experimental Result • Experiment on a real environment • Comparison with computer simulation • Analysis of performance evaluation results • Conclusion CQR2011

  3. Background • Spread of Wireless LAN • An increased demand for multimedia communications ⇒QoS control in wireless LAN environment becomes important network IP IP MAC WLAN application QoSpass Streaming server Various controls proposed in each protocol layer CQR2011

  4. Background ×Application：cannot correspond to many or new applications ×IP：necessary to change in the entire the network ×MAC：change of wireless LAN equipment ◎TCP：control on the network edge firewall can be passed network IP IP MAC WLAN application QoSpass Streaming server QoS-TCP(tries to guarantee the bandwidth based on TCP) CQR2011

  5. QoS-TCP • Aiming at quality improvements of streaming communications • Designed to assure a designated bandwidth • ssthresh is flexibly set by using the target bandwidth • cwnd is led to keep the target bandwidth, and kept large as much as possible even in packet loss • it avoids congestion collapsing cwnd Packet loss Packet loss QoS-TCP TCP ssthresh CQR2011

  6. TCP throughput Oligopoly(Unfairness problem of TCP throughput) • TCP throughput is not evenly divided among terminals • No data losses and TCP ACK overflow at AP buffer causes this unfairness • Higher throughput flow can send more, and Lower throughput flow can send less • The number of the terminals that becomes fair or unfair changes by buffer size of AP unluckey terminal fair unfair CQR2011

  7. Characteristics of AP • Evaluation environment • Buffer sizes of APs affect much on TCP/QoS-TCP throughput characteristics • Difficult to know buffer sizes of off-the-shelf APs • Vendors do not disclose such information • Estimated the buffer sizes • Imposing excess traffic to the AP and comparing input packets with output packets of the APs sender wired<100M> AP wireless<IEEE802.11g> receiver CQR2011

  8. Buffer sizes of APs Result of a measurement • 265.5 packets • Planex CQW-MR500 • 256 packets • BUFFALO WZR-AMPG300NH • 135.1 packets • BUFFALO WHR-HP-AMPG • 90.5 packets • NEC PA-WR8500N • 37.2 packets • BUFFALO WHR-AM54G54 • The buffer size is an average of 10 times • Buffer sizes of the 5 APs vary between about 30 and 300 packets • Buffer size effects on TCP throughput characteristics We should carefully decide buffer size in simulation CQR2011

  9. Previous Researches about QoS-TCP effectiveness has already been verified • Simulation and Real environments • wired networks • wireless networks(fixed) →An evaluation on moving terminals has not been performed yet • Evaluation of wireless networks(moving) • Measurements of normal TCP throughput on mobile teminals have already done →　characteristics of QoS-TCP has not known yet Characteristics of QoS-TCP on mobile terminal in wireless LAN CQR2011

  10. Problem and experiment on QoS control • １．Moving of mobile terminals influences the bandwidth guarantee of QoS-TCP • Radio field strength changes • disadvantage in the radio wave compared with the terminal that is already communicating • The number of the terminals changes • fair↔unfair • ２．Quality degration is confirmed to make QoS-TCP minimum • quality degradation happens to in the case of switching AP at Handover • Comparison of TCP and QoS-TCP Terminals in an environment of indoor/outdoor and simulation CQR2011

  11. Evaluation model Higher throughput flow can send more, and Lower throughput flow can send less 6 terminals in total do not cause unfair situation and 7 terminals in total do cause unfair situation QoS-TCP handover 20m AP1 AP2 Each data is sent in uplink TCP flow direction <802.11g> <802.11g> <100M> 2 data sending terminals 6 data sending terminals server CQR2011

  12. Channel capacity measurement • Radio interferences are measured in TCP maximum throughput • One mobile terminal is used to measure • Outdoor • The interferences is strong enough to reduce the link capacityeven it is close to the APs • Indoor • The emission power of the radio signal is adjusted in order to be well attenuated at the point of the HO AP1 AP2 AP1 AP2 100m 20m CQR2011

  13. Throughput QoS-TCP and TCP (outdoor) • TCP:Throughput is always less than or equal to the fair-share value • QoS-TCP :slightly more than fair-share throughput near AP1 , but throughput fails near AP2 and anywhere else • The radio interference dominates to decide , so QoS-TCP fails to guarantee a bandwidth in this case Hand Over AP1 AP2 CQR2011

  14. Throughput QoS-TCP and TCP (indoor) • TCP cannot acquire bandwidth after the handover, but • QoS-TCP can ⇒Even QoS-TCP joins the competition after 6 terminals dominate whole bandwidth, QoS-TCP can defeat the oligopoly. QoS-TCP gets bandwidth Hand Over 3competitive terminals 7competitive terminals CQR2011

  15. Comparison with computer simulation • About 12 times difference even though similar parameters are used Difference about 12 times total throughput HO HO CQR2011

  16. Analysis of performance evaluation results(1/2) • Congestion window • Packet dump data • Air • Wired sender TCP-Proxy QoS-TCP converter converter converter converter <wireless LAN> （IEEE802.11g） AP <wired>100M receiver CQR2011

  17. Analysis of performance evaluation results • Very rare but bursty MAC data loss event occurred in the air • No throughput degradation was aware (but really happened) • Good chance to grab bandwidth for new comers!! • Larger slow start threshold in QoS-TCP than TCP • So, QoS-TCP can rump up faster than TCP and defeat TCP throughput throughput throughput seconds mili seconds minutes Simulation: QoS-TCP has no advantage against the competitive flows because of no data packet losses CQR2011

  18. Conclusion Characteristics of QoS-Guaranteed TCP on Real Mobile Terminal in Wireless LAN • QoS-TCP is likely to guarantee a target bandwidth in mobile wireless environments Analysis of performance evaluation results • QoS-TCP cannot defeat competitive TCP in bit error free simulations • QoS-TCP in real situation is effective to guarantee throughput CQR2011

  19. Thank you for your attention!! CQR2011

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