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TDMA For Long Distance Wireless Networks

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In 2006 the UC Berkeley TIER Project studied the need to deploy network infrastructure to emerging regions. Their goal was to “address the challenges in bringing the Information Technology revolution to the masses of the developing regions of the world”. Out of that work came plans for WiFi Based Long Distance Networks (WiLDNet) that leveraged commodity 802.11 wireless parts to preserve cost savings. WiLDNets were specifically intended for deployments where station separation far exceeded normal 802.11 use (e.g. 30-100 kilometer station separation). A key component of the WilDNet design was the use of a Time Division Multiplex Access (TDMA) MAC in place of the standard DCF MAC that is part of the 802.11 specification.

About the same time the Intel Research Laboratory in Berkeley, CA developed the Rural Connectivity Platform (RCP). TIER was a joint project between UC Berkeley and Intel and the RCP was an offshoot focused more on easy setup, low maintenance, and production use. For TDMA the RCP project developed a unique scheme to leverage the capabilities of Atheros wireless devices to implement TDMA almost entirely in hardware. The scheme has proven to work very well and has been incorporated in commercial products. In 2008 the RCP software base was moved from Linux to FreeBSD and in 2009 Intel released the FreeBSD implementation of the TDMA software. This talk describes the protocols and algorithms as they appear in FreeBSD 8.0.

Slides and paper:

http://www.freebsd.org/sam/TDMAPresentation-20090921.pdf

http://www.freebsd.org/sam/FreeBSD_TDMA-20090921.pdf

Bio: Sam Leffler has been actively working with UNIX since 1975 when he first encountered it at Case Western Reserve University. While working for the Computer Systems Research Group (CSRG) at the University of California at Berkeley he helped with the 4.1BSD release and was responsible for the release of 4.2BSD. He has contributed to almost every aspect of BSD systems; most recently working (again) on the network subsystems. For the past few years he has focused on wireless networking—his work appears in open source projects and many commercial products.

This talk is part of the Computer Laboratory Systems Research Group Seminar series.

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