Wi-Fi mesh as an emergency radio network
Summary
In 2012 researchers at TU Darmstadt used wardriving to investigate whether private Wi-Fi routers in cities could form an emergency radio network for first responders. In half a square kilometre they found 1,971 Wi-Fi cells; with a range of 30 metres, each node had an average of ten neighbours and only 2 percent were isolated. However, the routers would need mesh firmware and a power supply that holds up in disasters.
Ideas
- The density of private routers in city centres is sufficient for a mesh network.
- A second, separate SSID could offer emergency radio alongside the private Wi-Fi.
- The network would break up into around 50 subnetworks that additional nodes would have to link.
- A sixth of the best-connected nodes could be removed without changing the topology.
Insights
- Existing infrastructure can make emergency networks possible if software and power cooperate.
- In disasters, the power supply is the real bottleneck, not radio coverage.
Facts
- The largest cluster comprised 71 percent of all nodes.
- With a range of only 10 metres, around 800 subnetworks formed; at 60 metres the number of neighbours rose to almost 36.
- 65 of the 1,971 cells already transmitted with a locally administered MAC address, i.e. as part of a multi-SSID system.
- 212 of the recorded cells transmitted without encryption, 129 with insecure WEP.
References
Critique
- The study calculates a topology from beacons; whether the connections hold up under load remained untested.
Remarks
- Freifunk networks have been putting similar mesh ideas into practice for years with OpenWrt and B.A.T.M.A.N.
Recommendations
- Plan emergency communication with its own power supply, for example by battery or solar.
- Test mesh networks under real load before relying on them in an emergency.
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