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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
2011/05/12 2
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
ConclusionCQR2011
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
applicationQoS pass
network
WLAN
IPIP
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
IPIP
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
2011/05/12 5
Packet lossPacket 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
2011/05/12 6CQR2011
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
2011/05/12 CQR2011 7
sender
receiver
AP
wired<100M>
wireless<IEEE802.11g>
Buffer sizes of APsResult 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
2011/05/12 CQR2011 8
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
2011/05/12 9
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
2011/05/12 10
Terminals in an environment of indoor/outdoor and
simulation
CQR2011
Evaluation model
6 terminals in total do not cause unfair situation and7 terminals in total do cause unfair situation
2011/05/12 CQR2011 11
AP1 AP220m
handover
<100M>
<802.11g> <802.11g>
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
2011/05/12 CQR2011 12
AP1 AP2100m
AP1 AP2
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
2011/05/12 CQR2011 13
Hand Over
AP1 AP2
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.
2011/05/12 CQR2011 14
Hand Over
3 competitive terminals
7 competitive terminals
QoS-TCP gets bandwidth
Comparison with computer simulation
2011/05/12 15
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
2011/05/10 16
<wireless LAN>
( IEEE802.11g ) <wired>100M
converter
converter
AP
converterTCP-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
2011/05/12 17
Simulation: QoS-TCP has no advantage against the competitive flows because of no data packet losses
CQR2011
throughput
minutes
throughput throughput
seconds mili 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
2011/05/12 18CQR2011