We ask if the ubiquity of WiFi can be leveraged to provide cheap

connectivity from moving vehicles for common applications such

as Web browsing and VoIP. Driven by this question, we conduct

a study of connection quality available to vehicular WiFi clients

based on measurements from testbeds in two different cities. We

find that current WiFi handoff methods, in which clients communicate

with one basestation at a time, lead to frequent disruptions

in connectivity. We also find that clients can overcome many disruptions

by communicating with multiple basestations simultaneously.

These findings lead us to develop ViFi, a protocol that opportunistically

exploits basestation diversity to minimize disruptions

and support interactive applications for mobile clients. ViFi uses a

decentralized and lightweight probabilistic algorithm for coordination

between participating basestations. Our evaluation using a twomonth

long deployment and trace-driven simulations shows that its

link-layer performance comes close to an ideal diversity-based protocol.

Using two applications, VoIP and short TCP transfers, we

show that the link layer performance improvement translates to better

application performance. In our deployment, ViFi doubles the

number of successful short TCP transfers and doubles the length of

disruption-free VoIP sessions compared to an existing WiFi-style

handoff protocol.

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In  ACM SIGCOMM

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