The Effect of First-Hop Wireless Bandwidth Allocation on End-to-End Network Performance

Lili Qiu, Paramvir Bahl, Atul AdyaMicrosoft Research

NOSSDAV’2002Miami Beach, Florida

2

Outline

• Motivate the problem• First hop wireless bandwidth

reservation schemes• Performance evaluation• Related work• Conclusion

3

Introduction

• IP telephony is becoming popular• With the growth of wireless technologies, an

IP-based portable phone is a compelling device for voice communication

IEEE 802.11

Internet

Wireless Access Point

AP

IEEE 802.11

AP

PDA PDAPDA PDAPDA

Wireless Access Point

PDA

Kyocera QCP 6035(CDMA) - Palm 3.5 OS

Nokia 9110 (GSM) - GEOS OS

MS SmartPhone - WinCE 3.0 OS

AudioVox Thera (CDMA2000) - PPC 2002 OS

Samsung I300 - Palm OS

Siemens SX 45 (GPRS) - PPC 2002 OS

Handspring Treo 180 - Palm OS (GSM)

MSR’s UCoM (802.11) - PPC 2002

49 million PDA-Phones by the year 2007 [Cellular News 1/23/02]

PIP

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Research Issues

• Design space– Power– Security– Mobility– Bandwidth this paper’s focus– …

• Wireless bandwidth management– Wireless technologies used in the first hop are still slow– Challenges

• End-to-end reservation is preferred for ensuring QoS• Little QoS support in the Internet reservation only at

wireless hops• Effectiveness of local reservation depends on location of

bottleneck

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Motivation:Throughput of Internet Paths

• How often is a wireless application traversing the Internet rated-limited by its Internet path rather than wireless hop?

• Analyze the Internet tcpdump traces collected at microsoft.com– Incoming & outgoing web traffic, software download

traffic, streaming media traffic

Date Time # pkts # clients

Dec. 20, 2000

6:53PM–9:01PM 100 million 134,475

Jan. 24, 2001 10:08AM -11:21AM 20.4 million 53,811

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Throughput of Internet Paths

0

20

40

60

80

100

1 10 100 1000 10000

Average throughput (Kbps)

Per

cen

tag

e o

f h

ost

s

Dec. 20, 2000 Jan. 24, 2001

• Different clients experience widely different throughput, from 1 Kbps to 10 Mbps • Over 30% clients have throughput less than 20 Kbps Internet path can become bottleneck • Useful to consider congestion level of the Internet when making the bandwidth allocation decision in the first hop

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Temporal Stability of Internet Throughput

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10

Max/Mean Throughput Ratio

Per

cen

tag

e o

f h

ost

s

Dec. 20, 2000 Jan. 24, 2001

Over 90% of the hosts have throughput variation within a factor of 2 Internet throughput is stable

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Our Approach

• Observation– Not efficient to reserve more bandwidth than what an

application would use.– An application may use less BW

• either because it generates data at slower rate • or because bottleneck is at other links (e.g. Internet).

• Approach– Passively monitor applications’ bandwidth – Adaptively modify allocated wireless bandwidth

according to usage

• Places to deploy the technique– Infrastructure (Access point/Access server)– Client (PDA)

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First-hop Wireless Bandwidth Reservation Schemes

1. No reservation: best effort2. R0: Reserve s3. R1: Reserve min(s, f*I)4. R2: Same as R1, except it periodically re-

adjusts allocations: the rate specified by the sourceI: Internet bandwidthf: tolerance factor to account for estimation error

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Performance Evaluation

• Simulations in ns-2• Senders use TFRC

[FHP00]• Compare the above four

reservation schemes• Three scenarios

– Congestion at wireless hop

– Congestion at the Internet path

– Congestion at both places

A B

Senders Receivers

6Mbps

Internet pathwireless hop

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Scenario 1: Congestion in the wireless hop

0

0.01

0.02

0.03

0.04

0.05

0.06

0 100 200 300 400 500 600

# incoming connections

Ave

rag

e b

and

wid

th

per

flo

w (

Mb

ps)

No Reservation Reservation with R0

Reservation with R1 Reservation with R2

First hop reservation maintains QoS when congestionoccurs in the first hop.

Simulation scenario:S = 48 KbpsI = 96 Kbpss: the rate specified by the sourceI: Internet bandwidthCongestion in the wireless hop

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Scenario 2: Congestion in the Internet path

0

50

100

150

200

250

300

0 50 100 150 200 250 300

# incoming connections

# ad

mit

ted

flo

ws

No reservation Reservation with R0

Reservation with R1 Reservation with R2

• R0 is wasteful.• First hop reservation is ineffective when congestion occurs in the Internet.

0

0.005

0.01

0.015

0.02

0.025

0.03

0 50 100 150 200 250 300

# incoming connections

Ave

rag

e b

and

wid

th p

er

flo

w (

Mb

ps)

No reservation Reservation with R0

Reservation with R1 Reservation with R2

Simulation scenario: S = 48 Kbps, I = 24 Kbps congestion in the Internet

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Scenario 3: Congestion at both Internet and wireless hop

0

50

100

150

200

250

300

0 50 100 150 200 250 300

# incoming connections

# ad

mit

ted

flo

ws

No reservation Reservation with R0

Reservation with R1 Reservation with R2

00.0050.01

0.0150.02

0.0250.03

0.0350.04

0 50 100 150 200 250 300

# incoming connectionsA

vera

ge

ban

dw

idth

per

fl

ow

(M

bp

s)No reservation Reservation with R0

Reservation with R1 Reservation with R2

Reservation based on Internet throughput performs the best.

S = 48 Kbps, I = 24 or 96 Kbps congestion at both places

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Scenario 3: Congestion at both Internet and wireless hop (Cont.)

• Use the throughput in the Internet trace for our simulation– Pick hosts from the Dec. 2000 throughput trace, and

assign their perceived throughput to the bandwidth of the Internet path

– Vary the bandwidth of the links according to the trace

• Estimate throughput using past measurements• Tolerance factor (f) = 1.5 • Desired sending rate of a source

– Either CBR: 16 Kbps, 24 Kbps, 32 Kbps, 48 Kbps– Or VBR: the rate of video traces we collected

• Poisson arrival & departure – mean duration = 8 minutes

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Scenario 3: Congestion at both Internet and wireless hop (Cont.)

Allocating bandwidth that adapts to the Internet path’s throughput is even better.

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1 1.2

Normalized quality

Perc

enta

ge o

f con

nect

ions

No reservation R0 R1 R2

0

100

200

300

400

0 500 1000 1500 2000 2500 3000 3500

Time

# ad

mitt

ed c

onne

ctio

ns

No reservation R0 R1 R2

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System ComponentsAllocation Server• monitors throughput and

re-adjusts reservation periodically

Access Server• Polices users

Option Allocation Access Pro

1 Client Client Easier to deploy

2 AP AP No need for client cooperation

3 Gateway Gateway

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Related Work

• Studies on Internet path properties– Internet throughput remains stable on the

time scales of minutes [BSSK97, ZDPS01]

• Admission controls– RSVP [ZDES+93]– Measurement-based admission control – Endpoint admission control [BKSS+00]

• Wireless QoS– IEEE 802.11e – Subnet bandwidth manager [RFC 2814]

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Conclusions

• Provide applications with better QoS without infrastructure support in the Internet

• Study several bandwidth allocation techniques for wireless hops

• Adaptive bandwidth allocation for first-hop wireless based on passive observation of Internet paths performs the best– Has better quality than no reservation – Admits more flows than naïve reservation

• Design choices• Applications

– Wireless real time applications

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Acknowledgement

• Venkata N. Padmanabhan• Scott Hogan• Rob Emanuel• Chris Darling• Al Lee