Providing Wifi for 900+ Users

May 21, 2010

 

Apart from great organisation, speakers, and coffee, conference delegates generally rate WiFi connectivity as one of the most important needs at a conference. So, while the word spread that the number of registered Net Prophet delegates (Net Prophet is a South African conference we sponsor) was fast approaching the 900 mark, we were meticulously plotting how we were going to provide free WiFi; whilst trying to figure out exactly how many devices would be connected on the day, and at any given time.

From last year’s conference (400 delegates), we learnt that balancing the load across eight 1mb/s connections was simply not going to cut it this time. We needed to find something that would allow 900+ delegates to freely tweet, upload, download, check emails, send emails and chat to their friends who were missing out on the conference.

[blackbirdpie url=”http://twitter.com/mikestopforth/status/13910019982″]
Some of the challenges that face conference WiFi are:

1. Providing enough back-haul Internet capacity
2. Limiting per user download and upload speed
3. WiFi coverage within the venue
4. Wireless interference
5. Wireless Access Point congestion

Net Prophet takes the form of a one day conference held in a large conference facility. We calculated that we would need an Internet back-haul link total with the capacity of about 20Mb/s down and 10Mb/s up to give the largely tech crowd a great experience. We provisioned this directly from our Data Centre in Cape Town via 2 5.8Ghz point to point wireless links to the roof of the conference venue.

Inside the venue we set up a Linux firewall to provide DHCP along with per protocol queuing to ensure that no single user was able to abuse the service and slow speeds down for others.

Quality of service needed to be assured and our techs set up a few ‘queues’ on the router. The router would evaluate traffic and put it into the relevant queue (email, Web traffic, torrents, and ‘other’), which we monitored throughout the day, allowing us to adjust the queues accordingly should any latency be experienced. We also prioritised bandwidth to websites we knew would be accessed during the day by most users like Twitter, Facebook, Twitpic, Bitly and a few others.

To cover the venue in a WiFi blanket we used technology from Xirrus in the form of 16 access points each, with the radio turned down to 50% and with a sectorized antennae to focus the signal. Due to the constraints of the 2.4Ghz technology it is important not to overload individual access points but rather try to spread the load across as many access points as possible.

[blackbirdpie url=”http://twitter.com/smagdali/status/13919804313″] When conference delegates arrive in the morning there is usually a surge in usage, as everyone turns on their laptops, iPhones and iPads. To manage this and ensure all delegates got a reasonable connection, we rate limited each wireless connection to 2Mb/s. During the morning session, there were on average 132 devices connected and we were downloading approximately 2Mbps – 4Mbps (30% of which was for email). After the first tea break, news obviously spread about the free WiFi connectivity, so we removed the limiting. The number of devices connected immediately increased to 165. Continuous downloading on the link then jumped to between 5 Mbps – 8Mbps (90% being Web traffic) with the maximum being 14.9 Mbps, but as much as 10Mbps for extended 5 minute periods.

Towards the end of the conference, Web traffic decreased to 4Mbps, email traffic virtually disappeared, and ‘other’ traffic increased. Interestingly enough, the lowest traffic – less than 2Mbps – was recorded during Richard Mulholland’s presentation (Social Media: The side effects), just proving that we all “Stopped. Listened and took thing in.”

Of the 900+ delegates in attendance, only 1 person made an attempt at a torrent, but that was only for about 20 minutes before we stopped him (or her). Other than that, it was a very responsible crowd!