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

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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

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

3
Background
network
IP
IP
MAC
WLAN
application
QoS pass
Streaming server
Various controls proposed in each protocol layer

• Spread of Wireless LAN
• An increased demand for multimedia communications
• ?QoS control in wireless LAN environment becomes
  important

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Background
network
IP
IP
MAC
WLAN
application
QoS pass
Streaming server

• Applicationcannot correspond to many or new
  applications
• IPnecessary to change in the entire the network
• MACchange of wireless LAN equipment
• ?TCPcontrol on the network edge
• firewall can be passed

QoS-TCP(tries to guarantee the bandwidth based
on TCP)
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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

TCP
ssthresh
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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
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Characteristics of AP

• 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

• Evaluation environment

sender
wiredlt100Mgt
AP
wirelessltIEEE802.11ggt
receiver
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Buffer sizes of APs

• 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

• 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

We should carefully decide buffer size in
simulation
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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
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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
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Evaluation model
Higher throughput flow can send more, and Lower
throughput flow can send less
QoS-TCP
handover
20m
AP1
AP2
Each data is sent in uplink TCP flow direction
lt802.11ggt
lt802.11ggt
lt100Mgt
6 data sending terminals
2 data sending terminals
server

• 6 terminals in total do not cause unfair
  situation and
• 7 terminals in total do cause unfair situation

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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 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

AP1
AP2
AP1
AP2
100m
20m
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Throughput QoS-TCP and TCP (outdoor)
Hand Over
AP1
AP2

• TCPThroughput 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

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Throughput QoS-TCP and TCP (indoor)
QoS-TCP gets bandwidth
Hand Over
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.

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Comparison with computer simulation
Difference about 12 times total throughput
HO
HO

• About 12 times difference even though similar
  parameters are used

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Analysis of performance evaluation results(1/2)

• Congestion window
• Packet dump data
• Air
• Wired

sender
TCP-Proxy
QoS-TCP
converter
converter
converter
converter
ltwireless LANgt (IEEE802.11g)
AP
ltwiredgt100M
receiver
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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
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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

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• Thank you for your attention!!