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December 28, 2010

NY Times Biffs It on Wi-Fi Conference Overload

The New York Times doesn't get to the heart of conference Wi-Fi problems: I can't tell you how frustrated I am about this rather facile article on problems with thousands of people all trying to connect at once to a Wi-Fi network (or networks) at dense public venues, such as keynote addresses at technology conferences. As someone who has spent a decade writing in depth about Wi-Fi, often for mainstream audiences, the Times piece disappoints me as it spreads myths and doesn't cast new light. It also ignores a couple key factors important in 2010. (Let's not even get into the fact that the picture with this article makes Steve Jobs look as if he's about to have an emetic event onstage.)

We have to go nine paragraphs into the article before we get to the "nut" paragraph, the one that states the reason it's being written at all. First, we wade through anecdotes of specific conferences, and quotes from tech smarty guy Jason Calacanis, who does not advertise himself as a Wi-Fi guru:

The problem is that Wi-Fi was never intended for large halls and thousands of people, many of them bristling with an arsenal of laptops, iPhones and iPads.

That's not quite true, although it's not completely incorrect. Even the first Wi-Fi flavor, 802.11b, was designed to be aggregated into "infrastructure" networks in which many access points with the same network name (Extended Service Set) could be roamed among by client devices. The 802.11g spec clearly recognized that wireless networks could be used by dense crowds. And 802.11n, one could argue, specifically deals with heavy usage by allowing multiple antennas to "beamform" or steer signals directly to clients, and "hear" more clearly by using multiple antennas to sift through competing signals.

(More technically, 802.11g split a network signal into many subchannels, any of which can be garbled and the rest get through; 802.11n multiplies the number of unique data streams that can be sent at once, as well as taking advantage of 802.11g's subchannel approach.)

Two grafs later, the reporter shifts to backhaul and wiring, noting that infrastructure in hotels may contribute. Then, in the next paragraph, finally gets to the heart of the problem:

Companies that install Wi-Fi networks sometimes have only a day to set up their equipment in a hall and then test it. They must plan not only for the number of attendees, but also the size and shape of the room, along with how Wi-Fi signals reflect from walls and are absorbed by the audience.

This is true. Not all companies that install conference Wi-Fi know how to build such networks well, but many do; they are hampered by constraints of time, equipment, and venue issues. However, many firms repeatedly install Wi-Fi networks in the same locations, so you would think that they would be able to learn from this, either in setting expectations or improving networks. (Please also read MuniWireless's post from a year ago on this topic, which includes an interview with Tim Požar about conference Wi-Fi. Tim was the troubleshooter brought in by TechCrunch in the 2008 conference Wi-Fail cited in the NY Times article.)

What's not mentioned until the penultimate paragraph (and then in a backhanded way) is the rise of 5 GHz networking. It's a gaping hole in this article, even though it's on the edge of being too techie to mention—except that the writer goes into a parenthetical about 2.4 GHz. Most laptops and some mobile devices can use 802.11n over 5 GHz. In the United States, there are 23 clear 802.11n 5 GHz 20 MHz-wide channels, 8 to 12 of which are commonly available in base station hardware. (The other 11 can be used, but require signal sensing that monitors for relatively unlikely military use in the vicinity. This sensing recognizes a lot of false positives, which makes the channels less usable.)

If you're one of tens of millions of people with a dual-band 802.11n router, you're using 5 GHz in your home or office. You might know (or have found out) that 5 GHz signals, because they are higher up the spectrum, don't travel as far. They attenuate more rapidly, which means that the signals becomes lost in noise faster than 2.4 GHz. In a convention hall, however, with line of sight to most access points, distance is less of an issue. 802.11n also contends well with signal bouncing, allowing it to work better than earlier Wi-Fi flavors using a unique path through space.

Thus, any conference Wi-Fi service firm that's not sticking in a sizable proportion of 5 GHz capable base stations, preset to nonoverlapping channels across the keynote auditorium or conference hall, is starting out at a deficit. Client devices that can use 5 GHz will preferentially switch to it if there's a strong enough signal. (Base stations currently don't have a spec that lets them tell clients to switch channels.)

There will be plenty of congestion in 2.4 GHz's three mostly nonoverlapping channels, because most smartphones can only use that band. (I'm not sure if any smartphone has 5 GHz built in yet, only tablets and slates, like the Samsung Galaxy Tab and Apple iPad.) Older laptops will also use that band. And the MiFi, which is also mentioned in passing despite being another key potential problem in convention keynote Wi-Fi mishigas.

The MiFi—for those who haven't heard of it—is a cellular router, the most popular on the market, that connects both to a cellular network for Internet access and operates as a Wi-Fi router. This allows a MiFi owner to connect from any device with Wi-Fi. It's a neat bypass. Sprint, T-Mobile, and Verizon also offer certain phone models that can act as portable hotspots in the same fashion.

All of these cell routers and mobile hotspot phones use 2.4 GHz, and create unique networks. The more unique Wi-Fi networks in the same area, the more trouble, because Wi-Fi uses different strategies to avoid conflicting with networks on the same and adjacent channels. This reduces overall throughput.

But it shouldn't be that big an effect, even with the hundreds in use at tech events, like the ones this year that Apple and Google had trouble with. The MiFi uses relatively low power, the backhaul is relatively low-bandwidth compared to the 802.11g standard (about 1 to 2 Mbps of cell backhaul compared to 20 to 25 Mbps of real Wi-Fi throughput), and the 802.11 specs actually do a fairly smart job of sorting things out.

One final problem: DHCP. This sounds even more obscure, and I was reminded of this re-reading the MuniWireless article from last year. As Tim Požar noted, some wireless service providers don't configure the server that hands out temporary IP addresses to wireless devices correctly. I've seen this many, any times. Some outfits rely on the Wi-Fi access points, a terrible idea; most of those can hand out a maximum of 253 addresses, if that many. An access point might be able to handle several hundred connections, but simply can't give out addresses.

In a correctly configured network, access points pass through DHCP assignment from a central server, but those servers can be misconfigured to limit to 253 addresses or fewer, too. A simple change could allow over 16,000 addresses from one server. (Technically, you'd modify the subnet mask to increase the pool from a /24 to a /16 on a private address range, as one strategy.)

What's most likely the problem is tech companies and conferences cheaping out. I don't mean spending very little, but less than what would solve the problem. I'm sure the firms that unwire events come in with bids that are as cheap as they can make them to be the low bidder, or have the conference organizer or sponsoring company ask, "How can we knock this price down?"

With the level of Wi-Fi use we're seeing, it's not impossible to build a good network for thousands of people in a small space. It may just cost more than anyone wants to spend. The line item in the budget for Wi-Fi needs to be connected up with the expected return on good publicity.

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You touch on a number of the mistakes and omissions in the NYTimes article, but one of the most important (at least in our NYCwireless experience) is the use of managed APs, like Cisco's 1140s.

Though they are a couple thousand $$ more expensive than independent APs, such systems centralize the management of radios in all of a network's APs, enabling dynamic RF usage and power.

We've deployed such equipment at a conference attended by 1000 people, and had both excellent signal availability and network usage with only a few APs in a large theater. And we did it in only a few hours. *AND* the network managed itself (thanks to the centralized software).

Managed APs and a properly configured traffic shaping router enabled us to serve the entire conference with 2 15/2 DSL lines with no downtime and very happy participants.

"Cheaping out" on equipment is a surefire way to build a network destined for failure, and companies that don't spend a little more on good hardware wind up spending a lot more on support costs and admin time.

Another important point: 802.11b. These slow stations take up lots of airtime, slowing down 2.4 GHz networks tremendously.

At IETF meetings the wifi was troublesome for many years, but that got solved to a large by deploying more access points in large rooms with partially overlapping channels (yes, sometimes overlap is better than non-overlap). Then 802.11n and 5 GHz came along and I haven't had wifi trouble at the IETF for years.

I agree with your's and Glenn's points. I go to IEEE 802 meetings where the Wi-Fi, managed by VeriLAN, works fine in rooms in which there are 400 people or so. The biggest bottleneck, when there is one, seems to be the pipe coming into the hotel.

Another commenter has already pointed this out, but the other huge consideration is disabling DSSS-modulated 802.11b and only using 802.11g which uses OFDM (a uses OFDM as well). The problem is that there are so many older phones which only negotiate 802.11b rates and use DSSS to save power (I'm honestly not sure what the reason is, but you can check for yourself that many old devices - even ones which advertise g compatibility - use b) and slow the whole network down as a result on the 2.4 GHz band. The conferences I've been to with competent techs usually set the 2.4 GHz network to G/N only, and thankfully prevent B devices from connecting.

You're spot on about 5 GHz and configuring a subnet properly so there are plenty of DHCP leases to give out. I can't even count how many conferences I've been to where 5 GHz worked perfectly and all the people around me with cheaper 802.11g only cards sat arms crossed not able to do anything.

People with MiFi devices also need to realize that they can still get online if they tether over USB, which is the default purpose for that port. Many opt to disable tethering and use it for charging, and join just their laptop to it - that's the kind of selfish spectrum hogging that leads to these problems, at least in 2.4 GHz band.

There are some very high-end APs I've seen MS deploy at conferences (the name escapes me, but the devices are circular and have 8 or more spatial streams with discrete radios) which are specifically targeted at this kind of application. I've never ever seen WiFi go down at those like I have others with more common (even Cisco I've seen crash with 2.4 Ghz band) equipment. At IDF Intel had an awesome screen that showed the Cisco management controller with utilization across each node on each slice of spectrum. That's the right way to do things.

Those round APs are from Xirrus, which has made a very good business in providing just this kind of offering for high-density areas, including colleges and companies. They use sectorized, slightly overlapping APs all built into a single housing. A single device can have up to 16 radios (up to 4 b/g/n and up to 12 a/n) with a separate antenna for each that pushes signal out over a segment of the airspace.

As someone who has been a part of the team that hosts large IT conferences, I can tell you that all this tech talk is a waste of your breath. Seems like techies love to figure out the technical side of the problem, but you don't really need to. Hotels and conference centers treat wi-fi as a profit center. Why don't conferences provide adequate wi-fi or any at all? The quotes I've seen are in the ball park of $90 per person. Do the math... $90 x 1000 attendees equals a bill of $90,000. Cha-CHING!

Most IT folks have already Verizon/ATT cards in their laptops so there isn't any pressing need to add another line item to the budget.

I've used Xirrus APs with larger events and even put one in my permanent event space and have not had any problems at all. With the permanent event space, the XN4 was able to handle a little less than 200 devices, 120 of which were actively streaming video on youtube at one time. I have also had news reporters and news cameramen using it to upload real time video and it did it without any problems.

Great post Glenn, as you have shown once again why the mainstream media is the last place to turn to for clarity or accuracy.

I've helped clients support enough events where Wi-Fi and Internet access were key. In the case of events like eComm and Office 2.0, we had Covad supply Pre-WiMax wireless broadband on a point to point basis is excess of 25 megs (I think we ended up at 40 or 45 megs) and in the case of Office 2.0 the producer used Swisscom to do the in building. Not one complaint, and nothing but high praise. That was in 2007 or 2008. For eComm this past spring in Burlingame, again Covad provided their wireless broadband to the property, and conference organizer Lee Dryburgh brought in a team that knew what they were doing. The coverage was spectacular and we tracked that on average the 350-400 attendees has 1.3 devices per person on average connected at most times. Nothing failed.

If done right, with the right hardware and the right person or team doing the engineering it can be done properly.

Thanks for this post. I was irritated as soon as I began to read the NYC article as it was purely a mainstream fluff piece riddled with inaccuracy.
In many instances event planners or hotel managers simply assume that their existing network has enough support for these users. It is not that Wi-Fi is incapable of support an event with so many people - that type of network needs to be planned in advanced, properly surveyed and designed. For example, high-end Xirrus APs that each support 1024 users (perhaps multiple on different channels...) and enough (temporary) bandwidth to support the load is a solution. The bottom line is that the time and expense that this requires simply is not in the budget for many events. That being said - technology conferences, etc. should probably begin to make well executed networks a priority....and media outlets should be a little more well informed before they front-page articles.

One reason why "enterprise" APs perform better in high density settings is that these products typically implement better rate adaptation algorithms. In a high density environment, it is important to differentiate between frame loss due to insufficient SNR (in which case dropping rate may help), and frame loss due to congestion (in which case dropping rate may make the problem worse). Since IEEE 802.11 does not require implementation of rate adaptation algorithms resistant to "congestive collapse" and WFA does not test for this, there are many WiFi implementations out there that perform poorly in high density environments. While "enterprise" APs typically address this issue, it still can seen in "consumer" APs and stations.

Nice article, Glenn. However I think your conclusion that nyt didn't get to the heart of the problem was off base. I think they served their target audience well, most of which are non-technical folks. From that perspective, most of your points are overkill for that audience. Perhaps a better approach to the nyt article would have been to expand on it rather than criticize it.

We can quibble about how much tech can be in mainstream articles--I wrote regularly for the New York Times from 1998 to 2006, so I understand what the editors want in a general audience article--but if you leave out salient facts, no matter how simply you explain them, there's no value in it.

The article started from the proposition that Wi-Fi cannot handle large audiences in small spaces. That is incorrect. Wi-Fi networks are used this way all the time successfully. The author focused on some well-publicized failures, and didn't examine whether those were exceptions or the rule.

Put in mainstream terms, present-day Wi-Fi is designed to be used (as one scenario) with the kinds of large crowds that attend technology company keynotes and events, and it costs a lot of money to provide service. The failure is in the economics (as several commenters note here), not the technology. That's what's missing from the article.

Small but important correction: it's the ESS (Extended Service Set) and not the ESSID (which doesn't exist.)

I have seen ESSID used for many years as a shorthand for the BSSID for a node in an ESS, but I can't find an authoritative source for that. I'll fix.

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