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November 28, 2007

Questions? We Have Answers

There's a lull right now in Wi-Fi related news, so let's open the floor to questions: Any nagging questions on Wi-Fi, cell data, WiMax, Google Android, or other wireless data technologies and services? Post your questions in the comments, and I'll try to answer them with the help of other experts in the field as needed.

Q from Andrew (see comments) about cellular networks: The answer you seek would fill volumes. Fundamentally, GSM and CDMA employ different ways of reserving frequencies for users on the network, but both specifications do reserve spectrum. There is no intentional contention, in which manner GSM and CDMA (and their third-generation flavors HSPA and EVDO) are akin to WiMax, which uses OFDMA to reserve data slots (either by time or frequency). GSM uses time division multiple access (TDMA) or multiplexing to reserve periods of time for each receiver; CDMA's very definition is code division multiple access, which assigns unique codes which allow multiple transmissions over the same frequency at the same time. See also reply from George Bednyakov in the comments.

Q from Piet: "I'm from Europe, but I was curious how widely spread free outdoor Wi-FI is in the US?": It varies tremendously from city to city. There are at least hundreds, perhaps over 1,000 hotzones in limited areas, such as downtowns, parks, or public squares across hundreds of cities. Often, a city or a chamber of commerce sponsors such areas. Most of these offer entirely free access or access for a limited period of time or at a restricted speed. Larger, city-wide deployments that are free are pretty scarce, as are city-wide deployments of all kinds. Notably, anywhere MetroFi has a network, they push the free, ad-supported option. Some other metro-scale Wi-Fi firms offer limited free service, too, but that's rare.

Q from Steve about Rhode Island's state-wide wireless initiative: The project stalled in spring 2007 when the state assembly declined to provide a $28m loan guarantee for building the network further. Many lessons were learned, the group behind the project notes, and it's not necessarily dead in the water. Steve asked specific questions about technology, frequencies, and so forth, but my understanding is that in the pilot stage, everything was malleable for testing purposes; no firm decisions about a precise set of deployment hardware or licenses had been decided, as far as I know.

Ref 0709Iphone FrontQ. from "toukoob" (see comments) about the security of data transferred over EDGE by and to an iPhone: EDGE is generally considered secure, although experts I've spoken to say that it's crackable with some real effort. So your neighbor or a committed cracker won't have the horsepower, but an industrial spy or a government agent would likely have a portable system that would given some amount of time. You can't break EDGE generically, but could capture and crack data from a particular phone at a particular time. I would love it if Apple and/or AT&T would offer a persistent VPN connection that worked regardless of the medium. NetMotion Wireless and other firms have had such systems for years that work on laptops and handhelds, and they simply require some basic client software and a server on the remote end, as well as an approach to IP address assignment that AT&T could easily manage.

Q. from Edwin (see comments) on current municipal Wi-Fi projects in some form: The best source of information about what's happening in city-wide Wi-Fi is MuniWireless. Now, the company and staff benefit from the municipal Wi-Fi industry by accepting advertising, running conferences, and selling reports and advice. However, in my experience over several years now with Esme Vos, the founder, and other staff writers and producers, I've never found a bias in the presentation of the facts they gather. MuniWireless is definitely a proponent of the notion of wide-scale, wide-area networking at low cost over wireless, but they're also good reporters. One measure of this is that their most recent report showed a huge decline in projected spending over previous estimates, but a big uptick over current year spending. They covered that decline in the estimate quite well.


I am familiar with WiFi, but am curious regarding how Cellular network operate. I have never researched cellular technologies and would like a quick overview of the differences.

For instance, it uses licensed frequencies, but is there contention for the medium amongst shared users or does each user get dynamically assigned a small frequency range to use for their call/data session? What are the differences between CDMA, EVDO, GSM, etc.?


Regarding Andrew's question, the most important concept of a cellular network is frequency reuse. In a cellular type communications network defined blocks of radio spectrum are reused in a defined geographic pattern. All transmitters in a cellular network are following a detailed pre-determined plan regarding transmitter frequency and timing to control interference between different users.

The details of the standards and software protocols to implement a cellular network are continually changing, but the underlying goal is well defined reuse of radio spectrum.


I'm curious how secure is the data I enter/send via Mail/Safari over the iPhone's EDGE network?

Since we can't yet easily create an SSH connection, would I be safer doing some non-SSL connections via EDGE rather than taking a chance in an open Wi-Fi?

Thanks for your time and help in this matter.

I'm from Europe but I was curious how widely spread free outdoor Wi-FI is in the US?

Can you provide an update on the statewide Wimax network in Rhode Island? What equipment have/are they deploying, licensed/unlicensed frequency, timeframe, progress, etc. Thanks.

Do you have any links that show current WiFi municipal projects, either in map form, project descriptions, or otherwise? I saw CNET's map, but it seems to be outdated. Also, the Wireless Internet Institute also has a project list, but the list obviously isn't current as well...


Since you have an iPhone picture in your post, let me remind everyone who has unlocked or jailbroken theirs, and installed an SSH server: your data is up for grabs. At least in Spain if you use Vodafone.

When you activate EDGE or GPRS, you are given a public IP address, which on some carriers has zero filtering. I have successfully established an SSH connection to my iPhone's GPRS-given IP, and since the default password is 'dottie', well, my entire device would be available for anyone to see (including the phonebook, for example). The attacker could install minicom and start sending premium SMS messages without me knowing...anyway, just food for thought.

The problem is not so much coming from a sophisticated attacker capable and willing to break the EDGE air link, but someone coming from the internet.