6. June 2016 VARIA

Technology and resilience of the network in Fürth Freifunk

Florian Schimmer from Freifunk Franken shows us the technology behind the Fürth Freifunk backbone. We start at the relay station. There are currently three NanoStations M2 (Ubiquiti) active there. The Freifunk firmware runs on these, which directly uses the BATMAN Advanced mesh protocol. The connection to the relay station takes place over a distance of around 800 m, which is soon to be converted to the 5 GHz band with Ubiquiti LiteBeams sector antennas.

MikroTik’s SXT 5 ac hardware is used in a radio link in Nuremberg, which is still under construction. The goal should therefore be a connection over approx. 700 m with a bandwidth of over 200 Mbit / s.
In the city center of Haßfurt only NanoStations Loco M2 are operated in the 2.4 GHz band. All Ubiquiti devices have been provided with the Freifunk Franken firmware. Thus, the routers only have to be supplied with power via PoE because they are connected to each other via mesh. Thanks to the adapted firmware, access point and mesh scenarios can be set up at the same time, so that the routers not only build a wireless bridge to other routers, but also serve many clients at the same time. So far, this structure has proven itself and up to 50 clients can be served per access point. All clients share the bandwidth; Website calls and various messengers are still stable and easy to use.

The city network

Several NanoStations are attached to the tallest towers in the city and build radio bridges to other NanoStations that have access to the VPN backbone. This means that the signal is available from several uplink routers.
Since the city center of Haßfurt mainly consists of a main shopping street, the entire city center could be covered with just one NanoStation. The radio links are quite stable at up to 1.5 km, although some of them go over an inhabited area.

For the optimal use of the provided tower in the “Neighborhood House Gostenhof” in Nuremberg, it was decided to supply the direct environment with three NSM2, which were loaded with the Freifunk firmware. Freifunk Fürth enables passers-by in the nearby park to easily use the network and, above all, provides residents with uncomplicated peering options in the 2.4 GHz spectrum. In contrast to this local supply, in which the 2.4 GHz band is used due to the costs and easy availability, the 5 GHz band was consistently used when connecting the site to more distant free radio locations.

For this purpose, three locoM5s and one NSM5 are operated with the original firmware from Ubiquiti. This has the advantage that the proprietary TDMA protocols from Ubiquiti and the original drivers for the WLAN hardware can be used. This usually gives the tower 3 to 4 uplinks over 0.5 to 1.5 km. Thanks to this basic infrastructure, the tower could also be used quickly to provide Internet access to refugees who were housed on the former Quelle site 1.6 km away. Internally, the different NanoStations are connected by a ToughSwitch, which both separates them into VLANs and feeds the PoE for the end devices.