Best-Case WiBro Performance for a Single Flow Shinae Woo , Keon - - PowerPoint PPT Presentation

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

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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 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 HSPA GSM

300km/h 120km/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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KT’s

IP Network KREONET Server GPS WiBro Network Client GPS

Experiment Set-up

1Gbps link

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Experiment Set-up

KT’s

IP Network KREONET Server GPS WiBro Network Client GPS

KT – KREONET MRTG graph (26 April, 19:40:14)

Link speed = 1Gbps

Hop number RTT (ms)

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RTT by the Hop

Hop number RTT (ms)

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Wireless link dominates e2e performance

RTT by the Hop

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Architecture of Our GPS System

GPS module U-blox LEA-5 LAN cable USB RS232

Experiment Environment

NMEA data 1 PPS

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Clock Synchronization in Our GPS System

GPS UTC time CPU clock ck time GPS signal per second by 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 methodology

Send 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 Mbps Uplink 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 buffer 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) Bandwidth (Mbps)

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
• ption is only 64KB

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Thank you!!

GPS LAN cable USB RS232