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

Remi Ando† Tutomu Murase‡ Masato Oguchi†

†Ochanomizu University,Japan‡ NEC Corporation

Outline

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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

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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

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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

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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

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Packet　lossPacket　loss

QoS-TCP　

cwnd

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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

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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

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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

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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

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effectiveness has already

been verified

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

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Terminals in an environment of indoor/outdoor and

simulation

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Evaluation model

6 terminals in total do not cause unfair situation and7 terminals in total do cause unfair situation

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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

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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

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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.

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Hand Over

3 competitive terminals

7 competitive terminals

QoS-TCP gets bandwidth

Comparison with computer simulation

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About 12 times difference even though similar parameters are used

Difference about 12 times total

throughput

HO

HO

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Analysis of performance evaluation results(1/2)　 Congestion window

Packet dump data Air Wired

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<wireless LAN>

（ IEEE802.11g ） <wired>100M

converter

converter

AP

converterTCP-Proxy

QoS-TCP

sender

receiver

converter

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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

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Simulation: QoS-TCP has no advantage against the competitive flows because of no data packet losses

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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

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Thank you for your attention!!

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