VoIPowering Your Office: Can VoIP Do Wi-Fi?

A first look into the wonderful, wacky world of unwired mobile VoIP.

By Carla Schroder | Posted Oct 15, 2007
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In last week's article I dismissed Wi-Fi (or, to be more precise, the IEEE 802.11 wireless networking standard) as being unsuitable for VoIP. However, the excellent Ted Stevenson, Enterprise VoIPplanet's own managing editor, informed me that's not quite so, and that there are some Wi-Fi implementations that integrate well with VoIP networks—or is it the other way around? In any case, today we're going to take a look at major roadblocks and pitfalls, and next week preview some working Wi-Fi IP phones and networks.

Wi-Fi hurdles
Integrating wireless phones into VoIP networks seems like a natural fit. The advantages are what everyone always wants: lower cost and greater convenience. Why not have a Wi-Fi phone that works just like your wired IP phones, and get free or low-cost phone service to anywhere? Well, the first problem is you need to connect to an IP network. It's not like using a cell phone (CDMA or GSM), where you just whip it out wherever you are with confidence that you can make and receive calls. A Wi-Fi phone needs to find an IP network.

So you might be traveling, and these days it's a rare hotel that doesn't have free Wi-Fi. And you can nearly always find a public library, Internet cafe, or coffee shop with public Wi-Fi. For some people this is good enough, and you can get some nice buys on Wi-F (or dual-mode, Wi-Fi-enabled) phones.

But is this sufficient? What if you're also carrying a cell phone? How many gadgets do you want to haul around with you?

OK then, you say, fie on Wi-Fi. I'm already paying for a cell phone and I get a good deal on long-distance calling. So what's wrong with integrating cell phones into my VoIP network? Nothing, except that you need PSTN integration to make this work, as most cell phones don't support IP (Internet Protocol). This is a perfectly workable solution; the roadblock for some people is PSTN integration costs money, so you don't get free IP calls on your cell phone.

[Editor's Note: Though it's a relatively new phenomenon, a number of proprietary vendors—WiFiMobile and Truphone, to name two—have launched services wherein this integration has been carried out on behalf of the customer. A downloaded application running on the dual-mode phone routes calls to the vendor's core IP network—over Wi-Fi, when in the presence of a Wi-Fi network, or over a 3G data connection when out of Wi-Fi range.

Another type of PSTN integration is what's called fixed/mobile convergence (F/MC), wherein a switching device—either in a mobile carrier's network or in an enterprise network—detects SIP registration of Wi-Fi-enabled dual-mode phones, routing calls to/from phones within Wi-Fi range, or over the cellular access network when outside Wi-Fi range. See today's VoIPplanet news story and next week's Part 2 to this article for more information.]

Pushing voice traffic over a data networks isn't a seamless fit. Packet-switched networks are more efficient than circuit-switched networks because they can carry a lot more traffic. (See VoIPowering Your Office with Asterisk: Giving VoIP Traffic the Green Light for more information.) But that extra carrying capacity comes at a price: out-of-order, dropped, and re-sent packets, all of which hurt voice call quality. This is a significant problem across wired networks.

Not enough security
Wi-Fi carries the extra penalties of inconsistent implementation across different vendors of networking gear, less reliability than wired networks, and more problems around interference. The biggest problem, in my estimable opinion, is no call security. Eavesdropping is trivially easy on wired networks, and magnitudes easier on wireless networks. Wise network administrators understand that IP networks are inherently insecure, and encrypt sensitive transmissions with SSL or SSH. These are standard for protecting data IP traffic, but as far as I know the only VoIP service provider that offers VoIP encryption is Skype. Skype's Wi-Fi phones support WPA2 and RADIUS encryption and authentication, which are very strong protections, but there is a catch- this only works with service providers that support Skype's Wi-Fi program, via WISPr (Wireless Internet Service Provider roaming). RADIUS requires a central authentication server, so there is no way you can wander into any random Internet cafe or hotel lobby and get an encrypted connection; they have to cooperate with Skype.

I'd say that while WISPr is ingenious and better than nothing, it's a dead-end. What we need is an encryption protocol that doesn't require a PKI (Public Key Infrastructure), but rather is incorporated into VoIP protocols and equipment, and that operates without user intervention. That (someday) just may be the ZRTP protocol, which is implemented in Zfone. ZRTP doesn't need the CPU power that a PKI does, and it doesn't require any user or administrator intervention. A major difference between ZRTP and a PKI is ZRTP only encrypts the call- it does not authenticate the user.

Don't feel safe on your cell phone—yes, modern digital cell phones encrypt calls. But it's with a weak and long-ago broken encryption method.

Wi-Fi promise
These are interesting times we live in. New technologies don't supplant old ones; rather they accumulate. Vinyl LPs, reel-to-reel, cassette, CD, mp3; Laserdisc, VHS, DVD, Tivo; analog telephones, digital telephones, Bluetooth, pagers, email, instant messaging, cell phones, Wi-Fi phones; stuff just keeps piling up. What does the future hold, all of this stuffed into a single device welded to our heads? Tune in next week to find out.

Resources
VoIPowering Your Office: Eavesdropping on VoIP Calls (Part 1)
VoIPowering Your Office: Eavesdropping on VoIP Calls (Part 2)

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