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Ke Huang, UMass Lowell 91.650 Spring 2011
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Augmen'ng Mobile 3G Using WiFi
By: Aruna Balasubramanian, Ratul Mahajan, Arun Venkataramani
Presenter: Ke Huang
1Tuesday, April 12, 2011
Demand for mobile access growing www.totaltele.com
2
h+p://www.readwriteweb.com
2Tuesday, April 12, 2011
Demand for mobile access growing www.totaltele.com
2
h+p://www.readwriteweb.com
900 million mobile broadband subscrip'ons today….
www.3gamericas.org
2Tuesday, April 12, 2011
Mobile demand is projected to far
3
3Tuesday, April 12, 2011
Mobile demand is projected to far
3
Current spectrum 409.5 MHz
Unallocated spectrum (including whitespaces)
230 MHz
Projected demand by 2016
800 MHz – 1000 MHz
www.rysavy.com
3Tuesday, April 12, 2011
Mobile demand is projected to far
3
Current spectrum 409.5 MHz
Unallocated spectrum (including whitespaces)
230 MHz
Projected demand by 2016
800 MHz – 1000 MHz
www.nyCmes.com
www.rysavy.com
3Tuesday, April 12, 2011
Mobile demand is projected to far
“In light of the limited natural resource of spectrum, we have to look at the ways of conserving spectrum” -‐-‐ Mark Siegel (AT&T)
3
Current spectrum 409.5 MHz
Unallocated spectrum (including whitespaces)
230 MHz
Projected demand by 2016
800 MHz – 1000 MHz
www.nyCmes.com
www.nyCmes.com
Reducing cellular spectrum u'liza'on is key!
www.rysavy.com
3Tuesday, April 12, 2011
How can we reduce spectrum usage?
1. Behavioral
2. Economic
3. Technical
blogs.chron.com
4
4Tuesday, April 12, 2011
How can we reduce spectrum usage?
1. Behavioral
2. Economic
3. Technical
blogs.chron.com
4
www.usatoday.com
4Tuesday, April 12, 2011
How can we reduce spectrum usage?
1. Behavioral
2. Economic
3. Technical
blogs.chron.com
4
www.usatoday.com
4Tuesday, April 12, 2011
Augmen'ng Mobile 3G using WiFi
Offload data to WiFi when possible
Focus on vehicular mobility
5
5Tuesday, April 12, 2011
Offloading 3G data to WiFi
6
6Tuesday, April 12, 2011
Offloading 3G data to WiFi
6
6Tuesday, April 12, 2011
Offloading 3G data to WiFi
6
6Tuesday, April 12, 2011
Offloading 3G data to WiFi
6
6Tuesday, April 12, 2011
Offloading 3G data to WiFi
6
6Tuesday, April 12, 2011
Offloading 3G data to WiFi
6
6Tuesday, April 12, 2011
7
Related work on mul'ple interfaces
Improving performance using handoffs based on current condi'ons
Reducing power consump'on by switching across mul'ple interfaces
7Tuesday, April 12, 2011
7
This work:1.How much 3G data can be offloaded to WiFi?2.How to offload without hur'ng applica'ons?
Related work on mul'ple interfaces
Improving performance using handoffs based on current condi'ons
Reducing power consump'on by switching across mul'ple interfaces
7Tuesday, April 12, 2011
8
Contribu'ons
Measurement: Joint study of 3G and WiFi connec'vityAcross three ci'es: Amherst, Seagle, SFO
System: Wiffler, to offload 3G data to WiFi while respec'ng applica'on constraints Deployed on 20 vehicles
8Tuesday, April 12, 2011
9
Measurement setup
Testbed: Vehicles with 3G and WiFi (802.11b) radiosAmherst: 20 buses + 1 car, Seagle: 1 car, SFO: 1 car
Soiware: Simultaneously probes 3G and WiFi for Availability, loss rate, throughput
Dura'on: 3000+ hours of data over 12+ days
9Tuesday, April 12, 2011
Open WiFi availability low, but useful
10
Availability (%)
Availability = frac'on of 1-‐second intervals when at least one packet received
10Tuesday, April 12, 2011
Open WiFi availability low, but useful
10
Availability (%)
86%
Availability = frac'on of 1-‐second intervals when at least one packet received
10Tuesday, April 12, 2011
Open WiFi availability low, but useful
10
Availability (%)
86%
11%
Availability = frac'on of 1-‐second intervals when at least one packet received
10Tuesday, April 12, 2011
Open WiFi availability low, but useful
10
Availability (%)
86%
11%
Availability = frac'on of 1-‐second intervals when at least one packet received
7%
10Tuesday, April 12, 2011
Open WiFi availability low, but useful
10
Availability (%)
86%
11%
Availability = frac'on of 1-‐second intervals when at least one packet received
7%
3G+WiFi combinaCon be+er than sum pf parts
10Tuesday, April 12, 2011
WiFi loss rate is higher
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Cumulative fraction WiFi
3G
Loss rate = Frac'on of packets lost at 10 probes/sec
11Tuesday, April 12, 2011
WiFi loss rate is higher
11
Cumulative fraction WiFi
3G
28%
Loss rate = Frac'on of packets lost at 10 probes/sec
11Tuesday, April 12, 2011
WiFi loss rate is higher
11
Cumulative fraction WiFi
3G
28%
8%
Loss rate = Frac'on of packets lost at 10 probes/sec
11Tuesday, April 12, 2011
WiFi (802.11b) throughput is lower
12
Cumulative fraction
Cumulative fraction
WiFi
3G
WiFi
3G
Upstream
Downstream
Throughput = Total data received per second
12Tuesday, April 12, 2011
WiFi (802.11b) throughput is lower
12
Cumulative fraction
Cumulative fraction
WiFi
3G
WiFi
3G
Upstream
Downstream
Throughput = Total data received per second
12Tuesday, April 12, 2011
WiFi (802.11b) throughput is lower
12
Cumulative fraction
Cumulative fraction
WiFi
3G
WiFi
3G
Upstream
Downstream
0.35
Throughput = Total data received per second
12Tuesday, April 12, 2011
WiFi (802.11b) throughput is lower
12
Cumulative fraction
Cumulative fraction
WiFi
3G
WiFi
3G
Upstream
Downstream
0.35 0.72
Throughput = Total data received per second
12Tuesday, April 12, 2011
WiFi (802.11b) throughput is lower
12
Cumulative fraction
Cumulative fraction
WiFi
3G
WiFi
3G
Upstream
Downstream
0.35 0.72
Throughput = Total data received per second
12Tuesday, April 12, 2011
13
Implica'ons of measurement study
Strawman augmenta'on: Use WiFi when availableCan offload only ~11% of the 'meCan hurt applica'ons because of WiFi’s higher loss rate and lower throughput
13Tuesday, April 12, 2011
14
Key ideas in Wiffler
Increase savings for delay-‐tolerant applica'ons
Problem: Using WiFi only when available saves ligle 3G usage
Solu'on: Exploit delay-‐tolerance to wait to offload to WiFi when availability predicted
Reduce damage for delay-‐sensi've applica'ons
Problem: Using WiFi whenever available can hurt applica'on quality
Solu'on: Fast switch to 3G when WiFi delays exceed threshold
14Tuesday, April 12, 2011
Predic'on-‐based offloading
D = Delay-‐tolerance threshold (seconds)S = Data remaining to be sent (bytes)
Each second,1. If (WiFi available), send data on WiFi 2. Else if (W(D) < S), send data on 3G3. Else wait for WiFi.
15
15Tuesday, April 12, 2011
Predic'on-‐based offloading
D = Delay-‐tolerance threshold (seconds)S = Data remaining to be sent (bytes)
Each second,1. If (WiFi available), send data on WiFi 2. Else if (W(D) < S), send data on 3G3. Else wait for WiFi.
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Predicted WiFi transfer size in next D seconds
15Tuesday, April 12, 2011
16
Predic'ng WiFi capacity
History-‐based predic'on of # of APs using last few AP encounters WiFi capacity = (expected #APs) x (capacity per AP)
Simple predictor yields low error both in Amherst and Seagle
16Tuesday, April 12, 2011
16
Negligible benefits with more sophis'cated predic'on, eg future loca'on predic'on + AP loca'on database
Predic'ng WiFi capacity
History-‐based predic'on of # of APs using last few AP encounters WiFi capacity = (expected #APs) x (capacity per AP)
Simple predictor yields low error both in Amherst and Seagle
16Tuesday, April 12, 2011
17
Fast switching to 3G
Problem:WiFi losses bursty => high retransmission delay
Approach:If no WiFi link-‐layer ACK within 50ms, switch to 3GElse, con'nue sending on WiFi
17Tuesday, April 12, 2011
Wiffler implementa'on
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Wiffler proxy
§ Predic'on-‐based offloading upstream + downstream§ Fast switching only upstream
Ø Implemented using signal-‐upon-‐ACK in driver
18Tuesday, April 12, 2011
19
Evalua'on Roadmap
Predic'on-‐based offloadingDeployment on 20 DieselNet buses in 150 sq. mi region around Amherst
Trace-‐driven evalua'on using throughput data
Fast switchingDeployment on 1 car in Amherst town centerTrace-‐driven evalua'on using measured loss/delay trace using VoIP-‐like probe traffic
19Tuesday, April 12, 2011
Deployment resultsData offloaded to WiFi
Wiffler’s predic'on-‐based offloading 30%WiFi when available 10%
20
File transfer size: 5MB; Delay tolerance: 60 secs; Inter-‐transfer gap: random with mean 100 secs
20Tuesday, April 12, 2011
Deployment resultsData offloaded to WiFi
Wiffler’s predic'on-‐based offloading 30%WiFi when available 10%
20
% Cme good voice quality Wiffler’s fast switching 68%
WiFi when available (no switching) 42%
File transfer size: 5MB; Delay tolerance: 60 secs; Inter-‐transfer gap: random with mean 100 secs
VoIP-‐like traffic: 20-‐byte packet every 20 ms
20Tuesday, April 12, 2011
21
Trace-‐driven evalua'on
Parameters variedWorkload, AP density, delay-‐tolerance, switching threshold
Strategies compared to predic'on-‐based offloading:WiFi when availableAdapted-‐Breadcrumbs: Future loca'on predic'on + AP loca'on database
Oracle (Imprac'cal): Perfect predic'on w/ future knowledge
21Tuesday, April 12, 2011
Wiffler increases data offloaded to WiFi
22
Workload: Web traces obtained from commuters
22Tuesday, April 12, 2011
Wiffler increases data offloaded to WiFi
22
Workload: Web traces obtained from commuters
14%WiFi when available yields ligle savings
22Tuesday, April 12, 2011
Wiffler increases data offloaded to WiFi
22
Workload: Web traces obtained from commuters
42%
14%
Wiffler close to Oracle
22Tuesday, April 12, 2011
Wiffler increases data offloaded to WiFi
22
Workload: Web traces obtained from commuters
42%
14%
Wiffler close to OracleSophis'cated predic'on yields negligible benefit
22Tuesday, April 12, 2011
Wiffler increases data offloaded to WiFi
22
Workload: Web traces obtained from commuters
Wiffler increases delay by 10 seconds over Oracle.
42%
14%
Wiffler close to OracleSophis'cated predic'on yields negligible benefit
22Tuesday, April 12, 2011
Even more savings in urban centers
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23Tuesday, April 12, 2011
Fast switching improves quality of delay-‐sensi've applica'ons
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24Tuesday, April 12, 2011
Fast switching improves quality of delay-‐sensi've applica'ons
24
58%
24Tuesday, April 12, 2011
Fast switching improves quality of delay-‐sensi've applica'ons
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40%58%
24Tuesday, April 12, 2011
Fast switching improves quality of delay-‐sensi've applica'ons
24
40%58%
73%
24Tuesday, April 12, 2011
Fast switching improves quality of delay-‐sensi've applica'ons
24
40%58%
73%
30% data offloaded to WiFi with 40ms switching threshold
24Tuesday, April 12, 2011
25
Future work
Reduce energy to search for usable WiFi
Improve performance/usage by predic'ng user accesses to prefetch over WiFi
Incorporate evolving metrics of cost for 3G and WiFi usage
25Tuesday, April 12, 2011
26
Summary
Augmen'ng 3G with WiFi can reduce pressure on cellular spectrum
Measurement in 3 ci'es confirms WiFi availability and performance poorer, but poten'ally useful
Wiffler: Predic'on-‐based offloading and fast switching to offload without hur'ng applica'ons
26Tuesday, April 12, 2011
26
Summary
Augmen'ng 3G with WiFi can reduce pressure on cellular spectrum
Measurement in 3 ci'es confirms WiFi availability and performance poorer, but poten'ally useful
Wiffler: Predic'on-‐based offloading and fast switching to offload without hur'ng applica'ons
Questions?
26Tuesday, April 12, 2011
Thank you!
27Tuesday, April 12, 2011
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