WiFi for OTA13 – What it Takes

WiFi for Over the Air 2013

Guest Post from Rob Pickering, remedy  

A few folks have commented (in a nice way) about the WiFi for Over the Air 2013 at Bletchley Park last weekend. It stood up pretty well to 100s of developers with lots of devices each and I’ve been asked a bit about how it was done this year…

Raw Bandwidth

Our biggest challenge was time. We got involved only a few weeks before the event and, story ironically, mind the week after the event Openreach were due to deliver a new 1Gbit/s fibre bearer to site that had been ordered months ago.

The current Internet capacity to Bletchley Park is pretty heavily used Mon-Fri by the on site technology businesses here and prior to the upgrade doesn’t have the 70Mbit/s headroom during the working day that we knew from previous experience would be eaten by OTA. Weekends are fine as the business usage goes down, but that crucial bit between 10am on Friday when OTA started and 6-7pm when the site residents drifted off for the weekend was a bit of a bandwidth gap.

Thankfully, our friends at Host-IT had suggested antennaa rather appropriate “over the air” temporary microwave link via a local tower block. They knew a company that could do the neat radio stuff so with a week to go before OTA, contracts were signed with Skyline Networks, access to the tower block arranged via the council and on Tuesday morning they arrived on site with cherry pickers to find a suitable location for the dish.

It took a while to find a decent location. Bletchley Park is pretty green and whilst it all looked OK on a map, there was practically nowhere on-site that didn’t have a tree blocking the line of sight. Drilling holes in listed buildings to provide Internet access via thick bits of co-ax is a bit frowned upon so it also needed to be somewhere that we could get easy access through a window or similar to put a small rack inside the building and connect on to the rest of our network. No joy in any of the obvious places, either no line of sight, no easy way to get cabling into the building, or no way to connect from there to the network we were putting together for OTA.

In the end we worked out that if we used the roof of the National Museum of Computing in H-Block, we could get down into their boiler room and from there connect to the Gigabit fibre that runs down into our main comms room. The microwave L2 was running at 150Mbit/s at installation so it all looked great.

We subsequently had a few problems with the actual achievable Internet speeds on the link that had ourselves and Skyline tied up until the early hours of Friday morning, but in the end everything went brilliantly with the bandwidth.


The WiFi challenges we knew plenty about from previous OTA events. The Mansion is a hard space to get radio capacity into because of its construction. The Leon’s just didn’t have WiFi in mind when they built extension after extension on to the outside of the buildings. Most of its “internal” walls started life as 60cm or more thick outside walls which means there is very little consistent 2.4Gz or 5GHz propagation horizontally between rooms. This wouldn’t be so bad but there is often excellent vertical propagation to the upper floors which now house lots of technology businesses that rely on their WiFi so we have to be pretty smart about how we manage spectrum, especially in the crowded 2.4GHz band.

Drilling holes in panelling and running permanent cable around decorative finishes in the downstairs rooms is apparently very naughty so we tend to be somewhat restricted to making permanent access point installations in the upstairs areas. Very careful surveying and manual colouring of the spectrum map gives us pretty good coverage downstairs foraverage conference use but OTA is anything but average.

This year we added four temporarily rigged access points to the Ballroom/Billiard Room area where lots of development was going on (two on the only vaguely available bits of 2.4GHz spectrum and two on 5GHz). Lots of velcro and cable ties meant that it could all be ripped out at the end of the event so that you would never know it had been there.

We also put a wired network into the Marquee for this event – made easier by relocating it a convenient 90M cable throw away from our nearest fibre in the Hut4 catering building. We really wanted to do this for last year, but there wasn’t the budget for it so we resorted on that occasion to directional antenna on nearby buildings which didn’t work at all well for OTA scale load.

ota13-tentThis year we pulled out the stops and put key bandwidth consumers like the AV folks and lecterns on hardwired connections and put 7 hardwired access points in themarquee (1 omni on 2.4GHz in each of the four corners of the tent and 3 on 5GHz in the middle and stage area). We could have used highly directional antenna to stripe the coverage inside the marquee but instead took a bet that the 2.4GHz omnis would be adequate provided enough folks used 5GHz. This also gave us the advantage that a reasonable amount of coverage leaked well outside the tent onto the lawn and camping area.

2.4GHz vs 5GHZ

Most cheap WiFi kit uses 2.4GHz spectrum. This spectrum is easiest to make work on a small scale as it has better propagation through objects so you get a better signal radius. It is also very crowded with only 4 useable 20MHz wide frequency bands and lots of noise and competing uses.

5GHz on the other hand has many more useable channels in most environments. It isn’t as easy to cover large areas from one base as it’s propagation is more limited, but this is a very good thing if you have lots of bandwidth hungry clients in a small area. You can deploy a high density of access points without any spectrum issues and without resorting to low power/directional antenna which are required to do a similar thing in the 2.4GHz band.

To make OTA WiFi work well we needed to get as many clients as possible onto 5GHz. This is a challenge as many devices only support 2.4GHz so we needed to get as many as possible of the devices that do support 5GHz onto that band. One technique we used was a bit of social engineering that I first saw at Google Campus in London. As well as the standard SSID, broadcast on all APs, we also broadcast a “Fast” SSID only on 5GHz and told people to use it. That way, folks with dual frequency devices were persuaded to associate their devices only with the 5GHz bases rather than letting the device make an arbitrary choice. Of course we also made sure that the 5GHz access points were faster by allocating them 40MHz bands and leaving the standard SSIDs on them so that hopefully 5GHz capable device would choose them anyway.

The good news is that all of this worked well as nearly 50% of all sessions were on 5GHz access points this year – thank you Apple & Google Nexus which seemed to be the most numerous devices with this support.

End results

This is what the Internet usage looked like over the 2 days of the event (5 minute average utilisation graphed):


A big spike overnight, but pretty much everyone had nodded off by 4am and a bit of a slow start on Saturday. Lots of frantic uploads and downloads up to the start of judging at 2:30 and then pretty quiet until the AV guys started pushing videos up just before we took the network to bits.


To everyone who helped us put this together:

Hostit and Skyline Networks for providing a 100Mbit/s link in less than a week!

The National Museum of Computing for letting us crawl all over their building to install it and steal the Museum Directors keys so that we could be in and out of their boiler room until 2am.

The Bletchley Park Estates team who did all the hard work getting an overhead cable into the Marquee and Matt who single-handedly rigged the marquee network on thursday evening while I was Internet router wrangling.

Matthew Cashmore and team for organising OTA. It was great to see the Mansion and grounds buzzing with innovation once again and a pleasure to be involved in the event.

The OTA13 Round-up

Marquee OTA13 smallerIt’s hard to believe that a whole week has gone by already, since the 6th edition of Over the Air at Bletchley Park, on the 27th & 28th of September. A huge cheer to all of you who attended, spoke, sponsored, donated prizes and participated in the Hack Day – YOU are the ones that make it awesome.

It was a more intimate event this year, with 465 in total attending – which is a pretty good turn-out considering we capped ticket sales at 450!

DevLabThis year’s highlights include the launch of DevLab and their DEVICE initiative, together with UCL Decide. DEVICE is part of the new IDEALondon centre in Shoreditch, and will provide developers with hands-on access to a wide range of devices for exploring and testing from across all platform ecosystems.

tnmoc_logoThe attendees of OTA13 also raised an amazing £6,000+ for the National Museum of Computing, thanks to a Justgiving Campaign by PayPal, where they matched the donations from attendees 1 for 1,  which will be matched again by a benefactor of TNMOC. (The campaign is still live – so make sure you get your donation in quick!!)

3d scanning3d printingThe Bletchley Park Mansion was augmented this year with a 3D scanning set-up brought out by Hercules Fisherman and his Thingmaker crew, and a 3D printer brought out by Terence Eden of O2 Labs. Watch out for many freaky plastic heads showing up on TwitPic in the near future…

As always an amazing range of creativity, collaboration, and knowledge-sharing was on display – too much to mention in a week of blog posts, let alone one round-up! You can get a pretty good feel for the event at this Eventifier Round-up, as well as our own Storify Page. (ping margaret at over the air dot org if I’ve missed anything…)


Speakers Presentations


The Over the Air Flickr Pool

Blog Coverage

PodCast Coverage


Video Coverage

Francesco Frison has put together a great clip of his experience of Over the Air 2013, including the tour of the National Museum of Computing:


On 36 hours of mobile development…

A Guest-Post event round-up

By Julie Gould, Citizen Cyberlab

Image you are asleep in your home, comfortably wrapped up in your duvet, oblivious to the burglar that is making their way along your drive.

Also imagine your dog is deaf and your burglar alarm has stopped working, how would you raise the alarm?? How would you know there has been a break in? How would you scare the intruder away?

The answer comes from the Nottingham University coders team at this year’s Over The Air event (27th and 28th September), an overnight Hack Day. Their solution: your bog-standard (a-ha) toilet.

Using an accelerator like the one in your phone, you can measure the ripples in the toilet bowl water, which are created by vibrations. If the ripples are sufficient to raise an alarm, the accelerometer would tell another device to automatically flush the toilet, leaving the burglar to think that you are awake and in the house, and hence frighten them away. Obviously.

This is just one of the weird and wonderful creations to come out of last weekend’s event at Bletchley Park.

Bletchley Park3Bletchley Park, a beautiful country house just a few hundred meters away from the rail tracks is the birthplace of modern computing. Seeped in code-cracking history, what better place than here to host a hack-fest weekend.

Dan Applequist, one of the ‘Three Hackateers’ that organised the event described OTA as “a celebration of software development as a creative discipline.”

OTAOTA is a combination of a traditional developer conference, with sessions led by people from within the community and an overnight Hack Day competition. The talks were about all sorts of things: relevant issues that the developers can use over the weekend, for example building applications on a Windows phone, or  something a bit more futuristic like white space radio, a new radio technology that might replace the wi-fi and GSM that we rely on today.

Groups of computer coders, hard-ware coders, soft-ware coders, tinkerers, gamers and more come together to learn, play, and work. And the results are quite unique.

I’m not a computer tinkerer myself, I understand how to use one for what I need it to do, but those that attend this event understand the ins-and-outs of modern technology, and can make it do some great things.

3D LED Cube 1One hacker put together a 3D LED cube that he could control using a roller ball. He had brought all the materials with him, soldered it all together, and then built some software on the day.

Another used his phone network to give a light instructions as to which colour to shine.

A third made a tracking device for a house pet so that the owner would know which room of the house the pet is in.

Air Pollution meter5An other group put together a device that would measure the level of pollution in the area you are in. You could combine this with a bike ride and GPS tracking system, and them know which areas you’ve travelled through have the highest levels of pollution. You can thus avoid the route to work with the worst air pollution, or provide your local council with more information on levels of pollution at different times of the day.

These are just some of the wonderful things created at the 6th edition of Over the Air. You may be thinking, what is the point? Why not make something financially viable? Well,that’s exactly opposite to what the event is all about. Although the things created at OTA may not become the next lucrative app for your phone, they may one day develop into something people will use every day. OTA was the first place where phones were turned into “light sabers”, which can now be found on many apps and games.

So who knows, maybe one day your toilet may become your bulgar alarm! But for the meantime, I would recommend a dog, or you know, a regular one!

Whilst I was there, I thought I would hack together a bit of a podcast about it. You can find it on the Pod Delusion episode 207 (4th October 2013).