Freifunk & Free Communication (Part 2)

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Technology and capacity of the Freifunk network in Fürth

Florian Schimmer shows us the technology behind the backbone of Freifunk Franken. We are starting at the relay station where three Ubiquiti NanoStations M2 are currently in use. These devices are running the Freifunk firmware and directly use the B.A.T.M.A.N Advanced Meshing Protocol. The network is connected to the relay station in 800 meters distance, which will soon be upgraded to a 5 GHz Ubiquiti LiteBeam antenna.

Freifunk Relay in Fürth, Photo: Christian Dresel

For another radio link that is currently set up in Nuremberg, MikroTik's SXT 5 ac hardware is used. The goal is a link over 700 meters with a bandwidth of more than 200 Mbit/s. In the city of Haßfurt, only NanoStations Loco M2 working in the 2.4 GHz band are used. All Ubiquiti devices were equipped with the firmware of Freifunk Franken. Therefore, the routers only need to be powered via PoE as they are connected in a mesh. Due to the custom firmware, access point and mesh scenarios can be set up simultaneously, with the result that routers can establish a wireless bridge to other routers and serve many clients at the same time. This setup has proven itself and can serve up to 50 clients per access point. The bandwidth is shared between all users, but browsers and messengers still run smoothly

The City Network
Several NanoStations are mounted on the highest towers of the city and establish wireless bridges to other NanoStations that have access to the VPN backbone. This way, the signals from multiple uplink routers are available.
As the city center of Haßfurt consists for the most part of a main shopping street, the whole city center could be covered with only one NanoStation. The radio links are fairly stable at distances of up to 1.5 km, though they cross populated areas.

For an appropriate use of the tower at Nuremberg's “Nachbarschaftshaus Gostenhof“, it was decided to install three NSM2 running the Freifunk firmware to provide free Internet to the neighborhood. This way, Freifunk Fürth allows pedestrians a simple use of the network and provides local residents with uncomplicated peering possibilities in the 2.4 GHz band. In contrast to such local provisions for which the 2.4 GHz band is used, the 5 GHz was used to connect the site to distant Freifunk locations.

For this purpose, three locoM5 and one NSM5 that run the original Ubiquiti firmware are used. The advantage here is that the original driver software and Ubiquiti's proprietary TDMA protocol can be used. Consequently, the tower can receive several uplinks over 0.5 to 1.5 km. Thanks to this basic infrastructure, the tower could also be used immediately to provide Internet to refugees at a nearby reception center. Internally, the NanoStations are connected via a ToughSwitch that enables both the separation into VLANs as well as the supply of PoE.

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