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 Characteristics of AP Buffer sizes of APs Previous Researches about QoS-TCP Problem and experiment on QoS control Experimental Result QoS-TCP Unfairness problem of TCP throughput on Wireless LAN Experiment on a real environment Comparison with computer simulation Analysis of performance evaluation results Conclusion 2011/05/12 CQR2011 2 Background IP IP network MAC WLAN application QoS pass Streaming server Spread of Wireless LAN An increased demand for multimedia communications Various controls proposed in each protocol layer ⇒QoS control in wireless LAN environment becomes important 2011/05/12 CQR2011 3 Background IP IP network MAC WLAN application QoS pass Streaming server ×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 QoS-TCP(tries to guarantee the bandwidth based on TCP) firewall can be passed 2011/05/12 CQR2011 4 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 2011/05/12 CQR2011 5 TCP throughput Oligopoly (Unfairness problem of TCP throughput) TCP throughput is not evenly divided among terminals 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 7 unluckey terminal 10 Throughput(Mbps) No data losses and TCP ACK overflow at AP buffer causes this unfairness 8 Thfoughput(Mbps) 6 4 2 0 1 2 Terminal ID 3 6 5 4 3 2 1 0 1 fair 2011/05/12 2 3 4 5 Terminal ID 6 7 unfair CQR2011 6 Characteristics of AP Evaluation environment sender wired<100M> Buffer sizes of APs affect much on TCP/QoS-TCP throughput characteristics Difficult to know buffer sizes of off-the-shelf APs AP wireless<IEEE802.11g> Estimated the buffer sizes receiver 2011/05/12 Vendors do not disclose such information CQR2011 Imposing excess traffic to the AP and comparing input packets with output packets of the APs 7 Buffer sizes of APs Result of a measurement 265.5 packets Planex CQW-MR500 256 packets 135.1 packets BUFFALO WHR-HP-AMPG 90.5 packets BUFFALO WZR-AMPG300NH We should carefully decide buffer size in simulation NEC PA-WR8500N 37.2 packets 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 BUFFALO WHR-AM54G54 2011/05/12 CQR2011 8 Previous Researches about QoS-TCP Simulation and Real environments effectiveness has already been verified 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 2011/05/12 CQR2011 9 Problem and experiment on QoS control １．Moving of mobile terminals influences the bandwidth guarantee of QoS-TCP Radio field strength changes The number of the terminals changes disadvantage in the radio wave compared with the terminal that is already communicating 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 2011/05/12 CQR2011 10 Higher throughput flow can send more, and Lower throughput flow can send less Evaluation model QoS-TCP handover 20m AP1 <802.11g> Each data is sent in uplink TCP flow direction AP2 <802.11g> <100M> 2 data sending terminals 6 data sending terminals server 6 terminals in total do not cause unfair situation and 7 terminals in total do cause unfair situation 2011/05/12 CQR2011 11 Channel capacity measurement Radio interferences are measured in TCP maximum throughput One mobile terminal is used to measure Outdoor 25 30 25 15 TCP-up 10 Throughput(Mbps) 20 Thfoughput(Mbps) Indoor 5 20 15 TCP-up 10 5 0 0 AP1 AP2 AP1 AP2 100m 20m The interferences is strong enough to reduce the link capacity even it is close to the APs 2011/05/12 The emission power of the radio signal is adjusted in order to be well attenuated at the point of the CQR2011HO 12 Throughput QoS-TCP and TCP (outdoor) Throughput of mobile node(Mbps) 16 14 12 10 Hand Over 8 6 QoS-TCP case TCP case 4 2 0 0 5 AP1 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 AP2 Distance from mobile terminal to AP(m) 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 2011/05/12 CQR2011 13 Throughput QoS-TCP and TCP (indoor) 12 Throughput(Mbps) 10 QoS-TCP gets bandwidth 8 Hand Over 6 QoS-TCP TCP 4 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Distance from mobile terminal to AP(m) 3 competitive terminals 7 competitive terminals 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. - 2011/05/12 CQR2011 14 Comparison with computer simulation Throughput(Mbps) 12 Difference about 12 times total throughput 10 8 6 simulation 4 real terminal HO 2 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 HO Distance from mobile terminal to AP(m) About 12 times difference even though similar parameters are used 2011/05/12 CQR2011 15 Analysis of performance evaluation results(1/2) sender Congestion window Packet dump data QoS-TCP Air Wired TCP-Proxy converter converter converter converter <wireless LAN> （IEEE802.11g） AP <wired>100M receiver 2011/05/10 CQR2011 16 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) throughput throughput throughput seconds mili seconds minutes 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 Simulation: QoS-TCP has no advantage against the competitive flows because of no data packet losses 2011/05/12 CQR2011 17 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 2011/05/12 CQR2011 18 Thank you for your attention!! 2011/05/12 CQR2011 19
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