WiFi-Reports: Improving Wireless Network Selection Jeffrey Pang (CMU) with Ben Greenstein (IRS)...
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Transcript of WiFi-Reports: Improving Wireless Network Selection Jeffrey Pang (CMU) with Ben Greenstein (IRS)...
WiFi-Reports:Improving Wireless Network Selection
Jeffrey Pang (CMU)with
Ben Greenstein (IRS)Michael Kaminsky (IRP)
Damon McCoy (U. Colorado)Srinivasan Seshan (CMU)
Problem: Commercial AP Selection
• tmobile
• attwifi (ap 1)
• attwifi (ap 2)
• seattlewifi
• linksys
• Free Public Wifi
• $3.99
• $9.99
• Free!
• Free!
• Which networks will run my
applications?
• Which ones have good performance?
• Quality
= ???
We often have many choices of wireless access points (APs),but little information about each
Jiwire.comHotspot database
Wifi-Reports
Wifi-ReportsDatabase
Bandwidth: 30 kbpsBlocked ports: Email
Bandwidth: 5 MbpsBlocked ports: None
community uploadsmeasurement reports
members downloadsummary statistics
Wifi-Reports
• tmobile
• attwifi (ap 1)
• attwifi (ap 2)
• seattlewifi
• linksys
• Free Public Wifi
• I need to use VoIP so this is the best network for me
Bandwidth: 300 kbpsBlocked ports: None
Bandwidth: 100 kbpsBlocked ports: None
Bandwidth: 300 kbpsBlocked ports: None
Doesn’t work!
Doesn’t work!
Bandwidth: 100 kbpsBlocked ports: Email, Skype
Bandwidth: 300 kbpsBlocked ports: None
Doesn’t work!
Wifi-Reports provides information about APperformance and application support
Doesn’t work!
Doesn’t work!
Bandwidth: 100 kbpsBlocked ports: None
Bandwidth: 300 kbpsBlocked ports: None
Bandwidth: 300 kbpsBlocked ports: None
Wifi-ReportsHotspot database
Bandwidth: 30 kbpsBlocked ports: Email
Bandwidth: 5 MbpsBlocked ports: None
Doesn’t work!
Research Challenges
Doesn’t work!
Doesn’t work!
Doesn’t work!
Doesn’t work!
Bandwidth: 300 kbpsBlocked ports: None • Location privacy
– Reports shouldn’t be linked, otherwise they can be used to track users
– But also need to limit fraud;e.g., 1 report per AP per user
– Solution: new ecash-like reporting protocol & robust summary functions
Research Challenges
Doesn’t work!
Doesn’t work!
Doesn’t work!
Doesn’t work!
Bandwidth: 300 kbpsBlocked ports: None
Bandwidth: 10 MbpsWorks great! (Really!)
• Location privacy– Reports shouldn’t be linked, otherwise
they can be used to track users– But also need to limit fraud;
e.g., 1 report per AP per user– Solution: new ecash-like reporting
protocol & robust summary functions
Research Challenges• Location privacy– Reports shouldn’t be linked, otherwise
they can be used to track users– But also need to limit fraud;
e.g., 1 report per AP per user– Solution: new ecash-like reporting
protocol & robust summary functions
• Location context– Performance dependent on location
with respect to AP– Wireless channel effects loss rate– Solution: estimate different loss regimes
w/ distributed measurements
Doesn’t work!
Doesn’t work!
Doesn’t work!
Doesn’t work!
Bandwidth: 300 kbpsBlocked ports: None
Bandwidth: 10 MbpsWorks great! (Really!)
100% loss 0% lossintermediate loss
WiFi-Reports Overview
WiFi-ReportsAccount Service
Independent Report Databases
Report on tmobile:Bandwidth: 1200 kbpsBlocked ports: None
Report on UBookstore Cafe:Bandwidth: 4000 kbpsBlocked ports: Email, Skype,…
• Users collect measurement reports when they use networks
• Reports are sent to databases for others to download
Questions and Challenges
• How useful would this system be in practice?– Do users have many choices of usable wireless networks?– Is there diversity in network performance/functionality?– Is performance stable enough to be predictive?– Are networks better for some applications but worse for others?– Do enough users use real networks to gather measurements?
• How do we limit “report fraud” and provide anonymity?– Not even the account service should be able to link a user’s reports to each other
(otherwise location privacy is violated)– But each user should only be able to report once per network
Part I: Measurement Study• We built a measurement tool to simulate
reports that users would collect– Bandwidth, latency, jitter, blocked ports,
number of other users, etc.• We measured all networks visible from:
– 13 hotspots near The Ave– ~7 days at different times of day
• Measurement procedure:– Sit near center of hotspot– Perform active spot measurements
(2-3 minutes per network)
shinka tea
tullys 1
starbucks 1
tullys 2
trabant
oasislounjin
yunnie bubble teasureshot
bookstore
cafeontheave
starbucks 2
cafesolstice
Our study is the first to examine pay networks and encrypted networks,
in addition to open networks
Results: Are there many APs?
Better
Results: Are there many APs?
Better
Results: Is there diversity?
Better
Results: Is there diversity?
Better
Results: Are measurements predictive?
Better
Results: Are there application trade-offs?
Better
Better
Better latency
Better bandwidth
Part II: Private and Accountable Reporting
• How do we limit “vote fraud” and provide anonymity?
• Requirements:– No one, even the account service, should be able to link a
user’s reports to each other (otherwise previous work says location privacy is violated)
– Each user should only be able to report once per network
Anonymizing Mix Network
Design SketchWiFi-Reports
Account Service
Report on tmobile:Bandwidth: 1200 kbpsBlocked ports: None
Independent Report Databases
tmobile
tmobileseattlewifi
CAFEONTHEAVE…
1. Client creates one token per AP2. Client blinds each token3. Account Service signs blinded tokens4. Client unblinds tokens…5. Client uses and measures an AP6. Client uses token to sign report7. Report is published via mix network
Report on tmobile:Bandwidth: 1200 kbpsBlocked ports: None
Report on tmobile:Bandwidth: 1200 kbpsBlocked ports: None
Report on tmobile:Bandwidth: 1200 kbpsBlocked ports: None
Design Sketch Details
• = random public key pair {Ktmobile, Ktmobile-1}
– Account Service signs the public key Ktmobile
– Private key Ktmobile-1 is used to sign reports can update reports
• Assumptions:– The account service only gives one identity to each user– Most users are honest
• Open issues:– Client must get all tokens signed before using them expensive
• If only get signed token after AP is used, use of the AP is revealed• Can obtain a subset of all tokens instead (e.g., all tokens for a city)
trade off between token signing overhead for more location privacy
Token Generation Time
• Time to generate tokens for all APs in one city(single threaded Xenon 3.4 Ghz server)
Resistance to Fraud
• CDF of Prediction accuracy (1 = most accurate)
Ongoing work
• Implemented Wifi-Reports service– Linux client exists– Currently implementing Android client.
Anyone want to help?
• MobiSys ‘09
Questions?
(Other summer projects)
Results: Is there diversity?
Better
Bloc
ked
port
= n
o m
easu
rem
ent
Results: Is there diversity?
Better
Bloc
ked
port
= n
o m
easu
rem
ent
Results: Are measurements predictive?
Better
Bloc
ked
port
= n
o m
easu
rem
ent