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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 Remi Ando† TutomuMurase‡ Masato Oguchi† †OchanomizuUniversity,Japan ‡ NEC Corporation
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
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
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
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
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
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
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
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
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
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
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
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
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
Comparison with computer simulation • About 12 times difference even though similar parameters are used Difference about 12 times total throughput HO HO CQR2011
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
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
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
Thank you for your attention!! CQR2011