Mobile Data Network Protocols
Reliable, Efficient Topology Broadcast Protocol for Dynamic Networks
SRI presents, proves correctness for, and evaluates a protocol for the reliable broadcast
of topology and link-state information in a multi-hop communication network with a
dynamic topology, such as a wireless network with mobile nodes. The protocol is
called Topology Broadcast based on Reverse Path Forwarding (TBRPF), and uses the
concept of reverse-path forwarding (RPF) to broadcast link-state updates in the
re-verse direction along the spanning tree formed by the minimum-hop paths from all
nodes to the source of the update. TBRPF uses the topology information received along
the broadcast trees to compute the minimum-hop paths that form the trees themselves,
and is the first topology broadcast protocol based on RPF with this property. The use
of minimum-hop trees instead of shortest-path trees (based on link costs) results in
less frequent changes to the broadcast trees and therefore less communication cost to
maintain the trees. Simulations show that TBRPF achieves up to a 98% reduction in
communication cost compared to flooding in a 20-node network.
Field Tests with TBRPF
As part of research activities supported by the Office of
Naval Research, SRI is currently conducting field tests of TBRPF jointly with UC Berkeley
using unmanned research helicopters and ground mobile robots. The objective of the tests
are to evaluate TBRPF performance in various mobility scenarios and to streamline its
efficiency and to assess its capability to support various command and control applications.
(for more information on TBRPF . . .)
Technologies for Next-Generation Mobile Communications
and Computing
SRI was the System Engineer & Integrator (SE&I) for
the Global Mobile Information Systems (GloMo) program of the Defense Advanced
Research Projects Agency (DARPA). DARPA initiated the GloMo program in
1995 to develop and demonstrate technologies to support mobile computing
and communications for the information-intensive warfare of the future. SRI worked
closely with DARPA program managers and the GloMo principal investigators on integrating
various hardware and software technologies developed in GloMo into several
major demonstrations for senior individuals in the government and the private sector. Automated Packet Radio Network Testbed
We have developed a color graphical user interface that controls the connectivity
of an RF switch matrix to which packet radios are attached. By manipulating
the graphical elements on the workstation, the user can adjust the link
topology of the packet radio network. A series of topology states can
be saved with timing information for later replay from the resulting batch
file, allowing for repeatable experiments that address the performance
of network algorithms stressed by rapidly changing network topologies.
Network Interface Unit
The NIU is a low-cost, flexible network
device that interfaces a user terminal or host computer to low-cost packet
radio networks. The NIU is designed to be flexible, so that other interfaces
can be added easily—either commercially available interface boards
or custom-designed boards that contain only the circuitry needed for a
specific interface. Thus, the NIU can serve both as an experimental packet
switch and as an IP router. The NIU has been transferred to a commercial
electronics company for manufacture and distribution.
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R&D Divisions