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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KT’sIP Network

KREONET

Server

GPS

WiBro Network

Client

GPS

Experiment Set-up

1Gbps link

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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

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 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

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Thank you!!

GPSLAN cable

USBRS232