by Tracy V. Wilson
Free stuff is good, and free stuff that you'd ordinarily have to pay for is even better. That's one of the reasons people have tried using Voice over Internet Protocol (VoIP) to make phone calls. With VoIP, you can make calls, even long-distance and international ones, for free. But until recently, VoIP had one pretty big limitation -- to make a call, you had to be at a computer.
New phones make it possible for people to place VoIP calls without being leashed to a computer. WiFi phones use the same wireless network technology that computers use, making VoIP a lot more portable.
This article will explore WiFi phones and their abilities, as well as the pros and cons of using them. We'll start with a quick review of VoIP and WiFi.
Understanding VoIP is easier if you have a basic understanding of how old-fashioned telephones work. Most people have used an ordinary "land line" phone so often that the process seems instinctive. You just pick up the phone, hear a dial tone, dial, talk and hang up.
But several things happen between you dialing the phone and the other person answering. To get from person to person, the call travels through the wires that make up the public switched telephone network (PSTN). Your local phone carrier routes your call through a series of physical switches that eventually connect your phone to the other person's. This is called circuit switching.
This isn't a particularly efficient way of making phone calls. The entire circuit between the two phones stays open during the conversation, even though only one person is talking at a time. It's also open when neither person is talking.
Packet Switching and VoIP
VoIP uses packet switching rather than circuit switching. Instead of leaving an entire circuit open during the whole conversation, it breaks the conversation into small packets of data. It then transmits that data over the Internet. Instead of monopolizing a circuit, packet switching sends and receives data as needed.
Let's say you and a friend who uses the same VoIP service are going to talk to each other. You're using analog telephone adapters (ATAs), which let you plug your regular phones into your computers. Here's what would happen:
You pick up the receiver, which sends a signal to the ATA. The ATA receives the signal and sends a dial tone to let you know that you have a connection to the Internet.
You dial the phone number. The ATA converts the tones into digital data.
Your computer sends the data to the VoIP company's call processor.
The call processor maps the phone number by translating it to an IP address. A specialized mapping program called a soft switch connects your ATA to your friend's. It sends a signal to your friend's ATA, telling it to ring.
Your friend picks up the phone, establishing a session between your computers. Each system knows to expect packets from the other.
The system converts your voices into packets of binary data. The normal Internet infrastructure treats the just like it would for an e-mail message or a Web page.
As you talk, the system transmits packets of data back and forth. The ATAs translate the packets into the analog audio signal that you hear.
When you finish talking, you hang up the receiver, closing the circuit between your phone and the ATA. The ATA sends a signal to the soft switch to terminate the session.
It's an efficient process -- and it doesn't tie up the line when it doesn't need to. It can also be free. If you're using a free service, like Skype, and calling someone else who also uses the same service, your call costs you nothing. But you might want to make phone calls when you're away from your computer, or you might just want to walk around while you talk.
Cordless VoIP
Some VoIP services offer a cordless handset that communicates with a base station that plugs into your computer's USB port. These are more like cordless phones than mobile phones. They're not really WiFi phones since they're not capable of connecting to a WiFi network.
With 802.11 networking, or WiFi, VoIP can go wireless. A WiFi phone has an antenna that transmits information to a computer, base station or wireless router using radio waves. An antenna at a base station or router picks up the signal and passes it on the Internet.
