best-case wibro performance

8/8/2019 Best-Case WiBro Performance

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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 workshopMeasurement 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

InchenKoreaAirport

ServiceArea

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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KTs

IP Network

KREONET

Server

GPS

WiBroNetwork

Client

GPS

Experiment Set-up

1Gbps link


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Experiment Set-up

KTs

IP Network

KREONET

Server

GPS

WiBroNetwork

Client

GPS

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

Link speed = 1Gbps


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Hop number

RTT(ms)

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RTT by the Hop


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Hop number

RTT(ms)

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Wireless link dominatese2e performance

RTT by the Hop


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Architecture of Our GPS System

GPS module

U-blox LEA-5

LAN cable

USB

RS232


NMEA

data

1 PPS


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Clock Synchronization in Our GPS System

GPS UTC timePU clock time

GPS signal

per second

by PPS

Packet sent orarrival event



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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



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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 !!!



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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 XPs default TCP socket buffer size, 17KB, isnot enough to utilize the WiBro link fully

How Does the Buffer Size Affect TCP Bandwidth?


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5 Mbps with Windows XPs

default socket buffer size

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How Does the Buffer Size Affect TCP Bandwidth?


64KB

Min 128 KB buffer size canfully utilize the link

Window Size(KB)

Bandwidth(Mbps)


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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



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One-way Delay of Downlink TCP Traffic

Decreasewith piggybacking

Increasewith queuing


Window Size (KB)


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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 XPs default size without TCP 1323 extension

option is only 64KB


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Thank you!!

GPS

LAN cable

USBRS232

best-case wibro performance

Documents