Apple's WWDC Wi-Fi Woes Point Up Need for Wireless Capacity
You probably already heard the news. Steve Jobs had trouble with Wi-Fi based demos at the Apple Worldwide Developers Conference. In all fairness, there were reportedly over 500 access points operating in the area. That being said, this problem was avoidable.
What was the problem? At a high level, it was a capacity issue. Wireless is a shared medium, meaning all users contend for the total available bandwidth. In general, the more users there are, the less bandwidth each user experiences.
What is the answer? For starters, Apple should have provided wireless access for attendees. I am not 100% sure this *didn't* take place, but from reading reports of all the rogue access points and Mi-Fi devices in place at the event, I would venture to say Apple didn't offer an alternative. Of course, if they offered attendee access, there are a whole host of security mechanisms they should consider putting into place to segment traffic, provide quality of service, etc.
So if Apple was going to deploy a wireless network for the attendees, how should they design it? Two words: for capacity. Start with 802.11n access points. They have a number of technical improvements that provide 5-6 times the bandwidth that legacy 802.11a/g APs provide on a per radio basis. You can read my previous blog post, "What Every IT Professional Should Know About 802.11n" for a better understanding of 802.11n technical improvements such as MIMO antennas, spatial multiplexing, and short guard interval.
However, 802.11n alone is not enough. The real "secret" to additional capacity is additional radios. Each radio provides its own capacity that can be shared by the total number of users. Here's where it gets tricky. There are only a certain number of "non-overlapping" channels available for use. There are 3 non-overlapping channels in the 2.4 GHz spectrum, and 24 non-overlapping channels in the 5 GHz spectrum. The Wi-Fi radio in the iPhone (3G, 3GS, and 4G) is only capable of operating in the 2.4 GHz spectrum, so Apple would want to encourage as many users to utilize the 5 GHz spectrum as possible.
How should they encourage users to utilize the 5 GHz spectrum? It sounds obvious, but provide plenty of 5 GHz access points. The clients (laptops, phones, tablets, etc.) make the decision of which AP they want to connect to. They make this decision on a number of factors to include signal strength and signal quality. If you provide a relatively high number of 5 GHz APs, clients will migrate to them. You can even reuse non-overlapping channels in the same physical space with careful channel planning and cell size tuning -- this is much easier in 5 GHz where you have eight times the number of non-overlapping channels.
Another way to get users to utilize the 5 GHz spectrum is through social methods. Announce that you have an official wireless network and ask users to use it instead of their own Mi-Fi or other rogue device ahead of time. If you provide access in both frequency bands, use a separate SSID for each band and use an SSID that naturally encourages people to use 5 GHz. For example, they could have an SSID "WWDC" in 2.4 GHz and a separate SSID called "WWDC-Fast" in 5 GHz. If you saw both of these SSIDs in your available wireless networks, which one would you pick?
Additionally, there are some technical methods to shift clients to 5GHz. Some vendors have a proprietary mechanism called "band steering" (or something similar). Even though clients ultimately make the decision of which access point to connect to, and if/when to roam, band steering is a method that Wi-Fi manufacturers use to place clients on 5GHz radios, where possible. This can be taken a step forward with "mode steering" where clients are grouped together on a particular radio based on which IEEE specification they use. For example, all faster 802.11n clients are grouped together so they do not have to slow down for legacy 802.11a/b/g clients.
Are there other design principles that could have helped Apple at the WWDC? Of course! A couple big ones that come to mind are implementing an integrated wireless intrusion detection/prevention system to contain rogue APs and utilizing a spectrum analyzer to monitor the RF environment. Perhaps I'll write about these in another post if there is enough interest. At the end of the day though, since wireless is a shared medium, there is no replacement for additional capacity ... and the best way to provide additional capacity is with additional radios.
ENDNOTE: For further reading on the importance of capacity, you can also read my blog post, "It's not about full bars, stupid".