Characteristics of QoS-Guaranteed TCP on Real Mobile Terminal in Wireless LAN Remi Ando † Tutomu Murase ‡ Masato Oguchi † † Ochanomizu University,Japan ‡ NEC Corporation

Outline 2011/05/122  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 2011/05/12  Spread of Wireless LAN  An increased demand for multimedia communications ⇒ QoS control in wireless LAN environment becomes important Various controls proposed in each protocol layer application QoS pass network WLAN IP MAC Streaming server 3CQR2011

Background 2011/05/12 × 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 QoS-TCP (tries to guarantee the bandwidth based on TCP) application network WLAN IP MAC 4CQR2011 QoS pass Streaming server

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 2011/05/125 Packet loss QoS-TCP cwnd CQR2011 TCP ssthresh

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 fair unfair unluckey terminal 2011/05/126CQR2011

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 2011/05/12CQR20117 sender receiver AP wired wireless

Buffer sizes of APs Result of a measurement  packets  Planex CQW-MR500  256 packets  BUFFALO WZR-AMPG300NH  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 2011/05/12CQR20118 We should carefully decide buffer size in simulation

Previous Researches about QoS-TCP  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 2011/05/129 effectiveness has already been verified 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 2011/05/1210 Terminals in an environment of indoor/outdoor and simulation CQR2011

Evaluation model 6 terminals in total do not cause unfair situation and 7 terminals in total do cause unfair situation 2011/05/12CQR AP1 AP2 20m handover QoS-TCP server 6 data sending terminals 2 data sending terminals Higher throughput flow can send more, and Lower throughput flow can send less Each data is sent in uplink TCP flow direction

Channel capacity measurement  Outdoor  The interferences is strong enough to reduce the link capacity even 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 2011/05/12CQR AP1AP2 100m AP1AP2 20m  Radio interferences are measured in TCP maximum throughput  One mobile terminal is used to measure

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 2011/05/12CQR Hand Over AP1AP2

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. 2011/05/12CQR Hand Over 3 competitive terminals 7 competitive terminals QoS-TCP gets bandwidth

Comparison with computer simulation 2011/05/1215  About 12 times difference even though similar parameters are used Difference about 12 times total throughput HO CQR2011

Analysis of performance evaluation results ( 1/2 )  Congestion window  Packet dump data  Air  Wired 2011/05/1016 （ IEEE802.11g ） 100M converter AP converter TCP-Proxy QoS-TCP sender receiver converter 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 2011/05/1217 Simulation: QoS-TCP has no advantage against the competitive flows because of no data packet losses CQR2011 throughput minutes throughput secondsmili seconds

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 2011/05/1218CQR2011

Thank you for your attention!! 2011/05/1219CQR2011