Electromagnetic Field 2022

In June 2022 we ran our first large-scale POTS (Plain Old Telephone Service) network at Electromagnetic Field (EMF) in Eastnor, Herefordshire. Electromagnetic Field describes itself as “a non-profit camping festival for those with an inquisitive mind or an interest in making things: hackers, artists, geeks, crafters, scientists, and engineers” and offers 3 days worth of talks, workshops and installations, 2 well stocked bars, as well as gigabit internet and mains power directly to your tent.

EMF first started dabbling with Telecoms in 2018 when there were site-wide DECT and GSM networks, as well as a small POTS network ran out of Sleepy’s tent, which inspired us to scale things up and run a site-wide POTS network.

Whilst we would have loved to have ran a real telephone network with pure circuit switched copper lines, the cost of cabling combined with electrical complications (EMF has 4 seperate power grids, and conductors must not span between two grids) make this prohibitive, so we cheated a little and used copper for the “last mile” and an IP based core.

The network consisted of 14x Cisco VG224s Voice Gateways and 9x Cisco 2811 ISR routers with FXS cards inserted, giving a total of 372 lines. The majority of the gateways were situated in “Datenklos” (Data Toilet) - Repurposed portable toilets that are used to keep power and networking distribution out of the elements.

Datenklo with Voice Gateway

For distribution we opted for RJ45 connectors as CAT5 cables are cheap and readily available, and we really wanted to avoid having any kind of punch down termination. For the Cisco VG224s this consisted of an RJ21 connector broken out into 12 individual lines and 3x trunk ports carrying 4 lines on a 4 pair cable.

RJ21 Breakout Board

We had a bunch of 50M CAT5 cables, RJ45 couplers, and RJ45 to BT socket adapters available for sale, but the majority of subscribers chose to lay their own CAT5 terminated into a master socket. We should have known the EMF crowd would already be familiar with such things…

All the Gateways communicated with a centralised Kamailio based SIP proxy which handled routing calls between other POTS users and the DECT network ran by Eventphone. A basic API handled the routing logic, and an Asterisk server provided some network announcements and engineering services, like a quiet line and echo test. SamMachin also set up a Jambonz Server - a self hosted Telecoms API platform allowing people to quickly setup interactive voice applications, and people created various fun dial in services.

Attendees bought a range of hardware, from a GPO 332 to a working Rabbit Phone and there were also several public phones strapped to poles around the site that we’d like to do more of next time.

Telos ATP1

Telephone No. 745

One of the most popular functions turned out to be faxing, with around 17 attendees bringing a fax machine and 200+ faxes sent, 100 of which went to @EMFFacsimile - a Fax to Twitter Gateway. A couple of attendees also bought Apple Newton PDAs and modems and got rather excited when they faxed between themselves, possibly for the first time in 30 years.

There were plans to provide site-wide Dial Up internet and ADSL covering one section of the site, however unfortunately we ran out of time - now we’ve got a large event under our belt, we have some optimisations in mind that should make the roll out much easier.

We’d also like to thank everyone involved with organising EMF, all the volunteers that help it run smoothly, the attendees that bring their weird and wonderful creations to show off, everyone that helped run a telephone network in a field, and everyone that played with telephones!

EMF has left us very much hungry for more, and we don’t want to wait until 2024 before we can play with telephones again. If you too want to play with telephones at an event, whether that’s in a field or in a building, please get in touch.

Finally, some stats:

  • 50 Active Lines
  • 600+ Calls ( Longer than 10 seconds)
  • 200+ Faxes
  • ~110 Fax2Tweets
  • ~17 Fax Machines
  • 10+ hours of calls
  • 50+ Calls to Cat Facts