NSDI '08 – Abstract
Pp. 105–118 of the Proceedings
Efficiency Through Eavesdropping: Link-layer Packet Caching
Mikhail Afanasyev, University of California, San Diego; David G. Andersen, Carnegie Mellon University; Alex C. Snoeren, University of California, San Diego
Abstract
The broadcast nature of wireless networks is
the source of both their utility and much of their complexity.
To turn what would otherwise be unwanted interference into an
advantage, this paper examines an entirely backwards-compatible
extension to the 802.11 link-layer protocol for making use of
overheard packets, called RTS-id. RTS-id operates by augmenting
the standard 802.11 RTS/CTS process with a packet ID check, so
that if the receiver of an RTS message has already received the
packet in question, it can inform the sender and bypass the
data transmission entirely.
We present the design, implementation, and evaluation of
RTS-id on a real hardware platform that provides a
DSP-programmable 802.11 radio. While limited in scale due to
restricted availability of the CalRadio platform, our testbed
experiments demonstrate that RTS-id can reduce air time usage
by 25.2% in simple 802.11b infrastructure deployments on real
hardware, even when taking into account all of the protocol
overhead. Additionally, we present trace-based simulations
demonstrating the potential savings on the MIT Roofnet mesh
network. In particular, RTS-id provides a 12% decrease in the
number of expected data transmissions for a median path, and
over 25% reduction for more than 10% of Roofnet paths.
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