Bad Connections Dog Google's Mountain View Wi-Fi Network 144
itwbennett writes "Google launched its Mountain View, CA public public Wi-Fi network in August 2006. It was one of the first public wireless Internet services in the U.S. and was intended to provide free service across the city. But in 2012, one year after Google signed a 5-year agreement to continue the service, it started a slow decline to the point of being unusable. 'We started noticing it in very large files, things like operating system updates, but now it's on files as small as 500 kilobytes,' said Rajiv Bhushan, chief scientist of pharmaceutical startup Livionex and a long-time user of the network. A recent test by IDG News Service resulted in a total failure to get a working Internet connection at a dozen sites around Mountain View, including in the city's main downtown area and directly in front of Google's headquarters." I've had disappointing results trying to connect to several other public wireless nets around the U.S., both privately sponsored and municipal. Do you know of any that work especially well?
Re:isn't wifi like the old layer 1 hubs? (Score:5, Informative)
(These are general ideas and may not be technically accurate... feel free to correct me)
There are several problems with WiFi technology itself. First, there is no contention management for wireless. When you're wired in, collisions are detected quickly, so you can saturate the connection near its theoretical limits without too many errors. (There's a promotional video about this from Meru Networks [youtube.com], but it is fairly educational.) By contrast, WiFi will roll through a larger bit of data and then ask for confirmation of receipt, which can lead to a lot of problems as radios talk all over each other. This is not a problem in regular office environments, where walls, floors, and furniture can provide separation so the radios can "hear" things that are closer. However, get into an open air environment and add a bunch of devices at once, and everything flatlines as the access points attempt to orchestrate several hundred devices in range, including interference from other radios within "hearing" distance on the same channel.
The second issue is one of limited channels. Originally WiFi was designed to move a tiny amount, and I think you could actually split off 802.11b into 11 discrete channels. As data needs grew, they consolidated 11 channels into 3 discrete channels for 802.11g (4 in the EU, I believe) and that's where it stands: a 3 lane road for 2.4GHz. 5GHz has more channels, depending on where you are in the world, but right now they are unreliable as the requirement for many of them is to be compatible with DFS, which means that if there is a certain signal being broadcast, your access points are expected to abandon that channel immediately. I think there are changes in the works from the FCC [fcc.gov] and although it only introduces 30% or so of new spectrum, it happens to cross multiple channels, so it may be like going from 9-12 channels to 20 or so. Combined with the more limited range of the higher frequency, having 20 discrete channels opens up a lot of options for basic broadband in public spaces. (Well, it did until the new ac standard came out, and I haven't even bothered to read it because these massive spectrum widths are going to be a nightmare, and I'm in a different line of work these days.)
However, none of this solves the "microcell" design of WiFi, where the client makes the decision on what radio to connect to instead of the access point. Your cell service, for instance, works well because the tower instructs the client so it can perform handoffs, reduce the data rates, and make other adjustments to keep things from choking up. I have sat and watched an iPhone cross over multiple access points and hundreds of feet to connect across a stadium for no explicable reason. (That's true for every wireless device, but I'm picking on iOS because they are notoriously noisy, always flooding the air with useless beacons, trying desperately to connect to stored wireless networks even when they aren't around.)
I have deployed Xirrus, Aruba, Extricom, Unifi, and some other products in dense situations, but as far as I know, the only pseudo non-microcell options available are from Extricom and Meru. Although I haven't used Meru, I can say that Extricom has been the most reliable in very dense environments, since they use some tricks to keep the air quiet, and they do not introduce beacon traffic with the addition of more radios. (Disclaimer: I have worked with the guys from Extricom quite a few times, and I think they are very capable, so take that opinion with a grain of salt.) Xirrus works pretty well in corporate environments, and their reporting interfaces are great, but I was disappointed that their sales staff continued to deny problems in 2.4GHz long after it was obvious that they didn't have a workable solution for super dense deployments. But maybe they just didn't know.
Anyway, ignoring all of that technical garbage, the
Not Surprising (Score:5, Informative)
There are dozens of reasons why Wi-Fi doesn't scale to the masses. Especially outdoors or in large spaces. Here are a few:
- Wi-Fi is half-duplex. Only one transmitter can broadcast on a channel at any given time. If the transmitting radio is slow (weak connection, older technology, bad-driver, etc...), then all other devices must wait for the transmission to end before they can get their airtime to transmit.
- A Wi-Fi radio that conforms to the Wi-Fi spec must co-operate when on the same channel as other wireless networks near it. This means that the google APs should be honoring the management traffic and broadcasts from other Wi-Fi radios near them. In a place like Mountain View, there is a *LOT* of Wi-Fi.
- 802.11n performance is dependent on multi-pathing. An AP on a pole in the middle of a park doesn't give much in the way of surfaces to reflect a signal off of. You end up at my first point- slow transmission, lower cell capacity.
- While two clients on an AP each can "hear" the APs transmissions, they may not "hear" each others'. Collisions galore.
- The ISM bands that Wi-Fi operates in are full of non-Wi-Fi interference. Wireless baby monitors are notorious for killing Wi-Fi, as are cheap wireless video cameras. Cordless phones,motion detectors, microwave ovens, remote control toys all play a part in the general noise within these RF bands.
Re:isn't wifi like the old layer 1 hubs? (Score:3, Informative)
First, there are three nonoverlapping channels for 802.11b/g. So there's 11 channels, but transmitting on channel 1 means that you are putting noise on channels 1-5; transmitting on channel 6 means that you are putting noise on 1-10; and transmitting on channel 11 puts noise on 7-11. If you transmit on channel 3, that means you are disrupting 1-8, so it's best to simply use 1, 6, and 11.
5Ghz doesn't have as much of a saturation problem because of the smaller distance that a usable signal travels. Sure, 24Ghz would be even better, but then I wouldn't be able to use the signal on my driveway or probably even my bedroom. I can see 24Ghz being good for apartment use, or college dorms, although dorms should have their own wifi.
Re:isn't wifi like the old layer 1 hubs? (Score:4, Informative)
Each channel is a slightly different frequency - and somewhat like an FM radio a decent wireless router/card will "tune in" on the frequency it's connecting on,and tune out the others, preventing neighboring signals from "talking over each other". IIRC it's recommended to leave one or two "dead" channels between overlapping hotspots to minimize crosstalk, but even adjoining channels have much better signal rejection that trying to establish two independent datalinks over the same frequency, which is what happens if your neighbors router is operating at the same frequency as yours. The situation is actually even worse than a hub - imagine you have multiple *completely unrelated* networks all trying to simultaneously talk over the same wire.
Of course with a few dozen overlapping hotspots you're going to have some unavoidable crosstalk, there's less than a dozen different wi-fi channels. However most hotspots are factory configured to run on the same channel, so moving a few channels away from the congestion can allow for a much better connection, especially if you're at a decent range from anyone sharing the same channel. There's even free software available (I forget the name) that will show you the number and strength of the signals on the various channels so that you can make an informed decision about which channel will likely have the least interference.
Re:isn't wifi like the old layer 1 hubs? (Score:4, Informative)
Re:The solution (Score:4, Informative)
That's not actually a completely daft suggestion. A lot of wifi gear tries to automatically pick the clearest channel, but usually sucks at doing it while in operation. Rebooting disconnects all clients and gives it a change to do a full scan of all channels before selecting one, possibly switching to a less congested frequency.
Re:The solution (Score:4, Informative)
Would it shock anyone to know I actually did this reboot to a malfunctioning public Wifi base station recently and it worked?
I had a client moving into a new commercial location where the local cable company (Shaw) has one of their public Wi-Fi terminals installed.
They did not have their own network connection yet (booked for a few days later) so we just joined their computer to the public network but it was horrible. The connection showed moderate to high packet loss which was strange because the base station was in the roof a few feet away. Even doing a ping test to first hop (the base station) was showing the packet loss problem. Increasing the packet size on the ping tests showed the problem was got worse as you increased the packets so anything that wanted a sustained download and not small little transactions was suffering worse effects.
So I went into the back, found the power injector for the base station and cut the power. Plugged it back in, and after the reboot it was working well. No more packet loss, and a usable connection.
Maybe Shaw needs to update the firmware on these Cisco base stations they are using.