The challenges in a network with vehicular clients are sharp drop in the connection and unpredictably and the difficulty of estimating the continuously changing channel quality.
The paper presents the design and performance measurement of diversity-based handoff protocol ViFi, a protocol that minimizes disruptions in WiFi network connectivity to support interactive applications from vehicular clients. The measurement study is for two commonly used interactive applications: VoIP and short TCP transfers of two vehicular mobile network testbeds; VanLAN and DieselNet in different cities. ViFi exploits macrodiversity (i.e connection with multiple basestation on the same channel simultaneously) and opportunistic receptions by nearby basestations to minimize disruptions for mobile clients. The challenge in designing ViFi is in coordinating among basestations that opportunistically receive packets. ViFi imposes inter-BS communication within limited bandwidth, minimum overhead, low latency per packet.
In ViFi, the client broadcasts the identity of the selected nearby BS as anchor that provides Internet access, the auxiliary set of BSes and the previous anchor. The old anchor transfers any unacknowledged packets that were received from the Internet to the new anchor that treats these packets as if they arrived directly from the Internet.
The paper investigates four practical and two ideal handoff policies, five of them are based on hard handoff strategy where the client associate with one BS at a time depending on different factors. Two performance measurements are used to evaluate the performance of these different policies: aggregate performance and period of uninterrupted connectivity where it has been found that more packets can be delivered, less number of interruptions and longer uninterrupted session can be achieved as with multi-BS handoff policy. The deployed prototype doubles the number of successful TCP transfers and doubles the length of disruption-free VoIP calls compared to a hard handoff protocol. However, it performs poorly in case of high number of auxiliary BSes and/or equal distance from the auxiliary BSes to the source and the destination.
The paper presents the design and performance measurement of diversity-based handoff protocol ViFi, a protocol that minimizes disruptions in WiFi network connectivity to support interactive applications from vehicular clients. The measurement study is for two commonly used interactive applications: VoIP and short TCP transfers of two vehicular mobile network testbeds; VanLAN and DieselNet in different cities. ViFi exploits macrodiversity (i.e connection with multiple basestation on the same channel simultaneously) and opportunistic receptions by nearby basestations to minimize disruptions for mobile clients. The challenge in designing ViFi is in coordinating among basestations that opportunistically receive packets. ViFi imposes inter-BS communication within limited bandwidth, minimum overhead, low latency per packet.
In ViFi, the client broadcasts the identity of the selected nearby BS as anchor that provides Internet access, the auxiliary set of BSes and the previous anchor. The old anchor transfers any unacknowledged packets that were received from the Internet to the new anchor that treats these packets as if they arrived directly from the Internet.
The paper investigates four practical and two ideal handoff policies, five of them are based on hard handoff strategy where the client associate with one BS at a time depending on different factors. Two performance measurements are used to evaluate the performance of these different policies: aggregate performance and period of uninterrupted connectivity where it has been found that more packets can be delivered, less number of interruptions and longer uninterrupted session can be achieved as with multi-BS handoff policy. The deployed prototype doubles the number of successful TCP transfers and doubles the length of disruption-free VoIP calls compared to a hard handoff protocol. However, it performs poorly in case of high number of auxiliary BSes and/or equal distance from the auxiliary BSes to the source and the destination.
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