When you think of Super Bowl 47, many things come to mind: the Ravens, the 49ers, Beyonce or the 30 minute blackout in the third quarter. Most of us won’t think of the massive wireless network the NFL poured money and time into creating to support 30,000 Wi-Fi users within the Superdome and the BYOD challenges that came with protecting such a massive network from rogue devices. Lucky for us network engineers, Jon Brodkin provides a great discussion of how the NFL set up and maintained the Super Bowl network in a recent article in Ars Technica.
To summarize, the NFL Wi-Fi team devised a system to handle 30,000 simultaneous Wi-Fi users. In order to make this work, they set up more than 700 wireless access points inside the stadium and 250 access points outside. To maintain wireless security, the NFL had intricate frequency coordination in place and all attendees were required to put their wireless devices through a frequency scan to be authorized. If any of these devices presented potential interference, the device was “remediated.”
Brodkin’s technical explanation of how such a large Wi-Fi network was set up and maintained is fascinating but it gets us thinking about how to maintain such a network long after the Super Bowl is over. How do you maintain a massive Wi-Fi network on a daily basis, not just for one afternoon/evening? To address this issue we have put together the following how-to guide for handling a Wi-Fi network for tens of thousands of people using multiple devices 24/7.
In a sense, you have an advantage in planning your wireless network for the enterprise because you can predict what kind of traffic will be on the network. This means that you should know how many users you will be adding, and what data they will usually access at any given time. To do this, use what you know about traffic patterns based on your baselining efforts.
As with the Superdome, you will need to determine how many access points are needed based on the number of Wi-Fi users you have. While this varies between access points (APs), the numbers should be well documented for supported simultaneous users and range. However, that’s only the starting point. Based on your policies, you may choose to allow BYOD, in which case it’s a safe bet that you can expect a total number at least twice the number of laptops, IP phones, etc., since users will bring in smart phones, tablets, and other equipment.
The physical environment itself will present some challenges, especially in older buildings with solid interior walls that absorb and distort the signal. Newer spaces tend to be wide open, with interior walls that are designed to be temporary. Fortunately, there are tools to help you with optimal placement, both on the site survey side, and on the AP side. Most modern APs use sophisticated internal antennas that actually rely on the signal bouncing around to create multiple paths for MIMO.
Once the environment is understood and an initial layout is determined, test it out at least one more time. Go to different environments and test out overall throughput and signal strength at key locations in your network. Remember that the performance is likely to be different once the office is full of people and equipment. Recently, Boeing did some Wi-Fi testing using potatoes to simulate a plane full of people. There’s likely no need to go to that extreme in your environment, but you should be mindful of where classic noise sources such as the department printer and the microwave in the break room will be located.
In larger spaces, or with larger numbers of devices, you’re going to need more than one access point. That’s where some of the challenges begin with maintaining a Wi-Fi.
The key enabler for large-scale Wi-Fi is central coordination, whether it’s through one or more controllers, or an intelligent protocol in controller-less equipment. Large-scale Wi-Fi is fundamentally different than a small network because the APs must coordinate to manage frequencies/channels, as well as user migrations between APs. The central coordination allows you as an administrator to configure your network as a large unit, as well as enabling cross-AP automation, such as automatic channel selection.
If you’re not familiar with how migration happens, it may be tempting to try to put all devices into a single L3 subnet, but remember that wireless is a shared medium. The broadcast storms that plague wired networks are especially hard on wireless, since a single L2 broadcast can be forwarded across all APs in the subnet, essentially utilizing all available bandwidth everywhere at once. Wireless vendors have methods of dealing with user migration transparently across APs, even if the user migrates onto an area with a different subnet.
We’ve written extensively on the management of wireless devices on the network. For example, check out a post about some of the security risks with consumer-grade wireless gear on your network and how you can combat the risks.
As Brodkin pointed out in the article mentioned earlier, one major problem facing the Superdome Wi-Fi team was the need for more channels. Most fans’ devices were only capable of operating in the 2.4GHz band. Interference is much more prevalent in that band, and the channel spacing is very small leaving only three non-overlapping channels for practical use, so all those users had to share three channels. However, the network did support 802.11n, which allows use of the 5GHz spectrum, so fans that had 5GHz capable devices were able to connect to more channels in a less noisy environment creating a much better user experience. This is an important take-away for enterprises as well.
If you’re looking at a Wi-Fi upgrade in the near future, try to make sure that as many of your devices as possible will support 5GHz. The frequency is much less crowded, which will lead to more effective bandwidth per user. However, most consumer devices still only support 2.4GHz, so you’ll probably need to support both.
The other thing to keep in mind for a future-proof network is that 802.11ac enterprise equipment should be available soon. Since it’s capable of supporting gigabit speeds, you need to think about the wired side of your network, and how much traffic the wireless will add to your core. The last thing you want is for your shiny new high-speed Wi-Fi to be bottlenecked by a slow uplink.