best-case wibro performance for a single flow 1 micnet 2009 shinae woo †, keon jang †, sangman...
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Best-Case WiBro Performance for a Single Flow
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MICNET 2009
Shinae Woo†, Keon Jang†, Sangman Kim† Soohyun Cho*, Jaehwa Lee*, Youngseok Lee ‡, Sue Moon †
Nov 23, 2009
† Computer Science Department, KAIST
‡ School of Computer Science and Engineering, Chungnam National University
* KT Central R&D Laboratory
AAF workshop Measurement Session
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• Provides high-bandwidth mobile data service• Served by KT and SKT in Korea• Being deployed in US, India and Japan
What is WiBro (Mobile WiMAX) ?
Seoul
Han River
Inchen Korea Airport
Service Area
50km
Population 20,000,000
WiBro users 200,000
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• Speed : Cellular networks < WiBro < WiFi• Mobility : WiFi < WiBro < Cellular networks
Market Positioning of WiBro (Mobile WiMAX)
WiFi
Mobility
Speed
WiBro
HSPAGSM
300km/h120km/h
144Mbps
35.44Mbps
14.4Mbps
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• IP-based packet-switching in the core• Uses 2.3GHz frequency, OFDMA
- Multiple users can access same time• Uses TDMA for up/downlink b/w allocation• 5 QoS classes implemented, only BE used
now
Characteristics of WiBro (Mobile WiMAX)
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Background
Motivation
Experiment Environment
Analysis Basic characteristics of WiBro
TCP Performance over WiBro
Conclusion
Outline
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Motivation
• Experiments on commercial network- Hard to pinpoint major factors affecting performance
• To know the baseline of WiBro performance- Focus on the performance of a single flow- Assume no competition and interaction between flows
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Experiment Set-up
KT’sIP Network
KREONET
Server
GPS
WiBro Network
Client
GPS
KT – KREONET MRTG graph (26 April, 19:40:14)
Link speed = 1Gbps
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Architecture of Our GPS System
GPS moduleU-blox LEA-5
LAN cable
USBRS232
Experiment Environment
NMEA data
1 PPS
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Clock Synchronization in Our GPS System
GPS UTC timeCPU clock time
GPS signal per sec-ondby PPS
Packet sent or arrival event
Experiment Environment
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Basic Characteristics of WiBro
TCP Performance over WiBro
• How different is WiBro from WiFi and cellular networks?• We use UDP to measure min and max one-way delay
- Min one-way delay = best-case w/o queuing- Max one-way delay = represents queue size
• Do we get theoretically maximum 35.44 Mbps over WiBro?
- Vary send and recv window sizes
Analysis Overview
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Minimum one-way delay
• Definition : delay without queuing= transmission delay + propagation delay + scheduling delay (at ACR )• Measurement methodologySend 40 byte packet every 40ms
• Measurement outcome:
- Downlink: 14ms- Uplink:100ms
Basic Characteristics of WiBro
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Bandwidth and Queuing Delay of WiBro
Downlink 10 MbpsUplink 2.5 Mbps
Large queuing delay
• We saturated link with UDP traffic
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Queue Size of WiBro links
• Queue size decides the queuing delay!!• With full queue,
Queue size = (max. one-way delay) * (bandwidth)• Measured queue size in each direction,
- Downlink 961ms * 9603Kbps = 1126 KB- Uplink 417ms * 2628Kbps = 137 KB
If bandwidth temporarily decreases to 1 Mbps,
queuing delay can increase up to 10 s !!!
Basic Characteristics of WiBro
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TCP performance over WiBro
• WiBro link has high bandwidth-delay product• TCP need socket buffer size of at least bandwidth-delay
product ex) Window XP’s default TCP socket buffer size, 17KB, is not enough to utilize the WiBro link fully
How Does the Buffer Size Affect TCP Bandwidth?
5 Mbps with Windows XP’s default socket buf-
fer size
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How Does the Buffer Size Affect TCP Bandwidth?
TCP performance over WiBro
64KB
Min 128 KB buffer size can fully utilize the link
Window Size(KB)
Band
wid
th
(Mbp
s)
TCP get the same bandwidth with UDP
Auto-tuned buffer works well in WiBro
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Auto-tuned TCP Socket Buffer in Ubuntu
TCP performance over WiBro
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One-way Delay of Downlink TCP Traffic
Decrease with piggybacking
Increase with queuing
TCP performance over WiBro
Window Size (KB)
• Developed cheap GPS module with sub-millisecond accuracy• Showed that WiBro is high bandwidth-delay network
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Our Contributions
Down Up
Bandwidth 10 Mbps 2.5 Mbps
Min Delay 14 ms 100 ms
Buffer Size 1126 KB 137 KB
High
Long
Big
• To fully utilize WiBro network, min 128KB or more TCP buffer size is needed
- Windows XP’s default size without TCP 1323 extension op-tion is only 64KB