Voice over IP

Wireless VoIP
Now that you've got a taste of what VoIP can do, you might be wondering why this discussion is relevant to mobile and wireless users. The answer is that the application and protocols work equally well over wired or wireless networks. Using PCPhone, I've been able to use my home office 802.11b wireless network to make calls from a Tablet PC. You can even make a VoIP call from a Pocket PC, using SJ Labs' SJphone, which Figure 2 shows and which is a Windows CE program that functions as a client for both SIP and H.323 connections.

For several years now, we've heard predictions about convergence devices—those that merge the functions of a cell phone and PDA. Such devices exist, but they're expensive, typically tied to one particular cellular provider, and often have limited PDA functionality. With VoIP applications, you can turn any Pocket PC, Tablet PC, or notebook PC with audio hardware into a convergence device, as long as you remain within the range of an 802.11b Access Point (AP).

VoIP Performance
Not every Internet connection works with VoIP—in particular, firewalls and gateways that use Network Address Translation (NAT) can be problematic. Depending on the protocol you use, ports on the firewall must be open to permit the creation of VoIP sessions. PCPhone provides a Network Settings test, which can help determine whether a particular Internet connection will work; I ran the test on my home office wireless LAN (WLAN), which uses NAT, and the connection works just fine. As of this writing, SJphone doesn't support NAT, but the company is promising to support NAT traversal in future releases.

Network performance can also be a concern. Before you run any VoIP application, you should perform a network response test (e.g., Ping) against the IP address of the PSTN gateway (or a typical target PC for a PC-to-PC connection). Any response that takes longer than 250 milliseconds (ms) round-trip will probably produce unacceptable results.

Corporate and enterprise IT professionals will be concerned about bandwidth requirements and scalability. According to Windows XP's built-in network monitor, VoIP calls use no more than 1 percent of typical 802.11b bandwidth (about 100Kbps), so one 802.11b wireless AP can support as many as 100 simultaneous VoIP calls. Of course, such high call volume will negatively affect network response for other applications. However, assuming a more reasonable number of callers, the performance effect should be negligible.

In addition to sending VoIP calls through a VoIP gateway, you can also receive incoming PSTN calls on a computer through a VoIP gateway, which eliminates the need for a telephone on a user's desk. However, this configuration is beyond the scope of my personal experience and might require a static IP address. Personally, I've found that using PCPhone for outgoing calls frees up my analog telephone to receive incoming calls—in effect, giving me two phone lines (the DSL line I use for Internet access carries the outgoing calls).

I've heard horror stories from several users of earlier VoIP systems, which typically delivered poor call quality with severe echoes and long delays. I haven't experienced these problems with deltathree's service or in my own experimentation with VoIP applications on the local network segment, but as the saying goes, your mileage may vary.

VoIP Savings
I haven't been able to completely wean myself from the habit of reaching for my telephone handset. Nevertheless, during the past 3 months, I've been able to cut my long distance bill in half. I expect to lower my bill even further as I become increasingly comfortable using VoIP instead of a traditional phone.

Enterprise users might be able to achieve even greater savings. Many corporate calls take place between employees in different offices. Almost invariably, these employees are sitting at desks in front of PCs. As a result, these calls can be made from computer to computer, at essentially no cost beyond the investment the company has already made to provide Internet access.

I've experimented with using VoIP to make calls while away from my office. I've had great success testing VoIP on a neighbor's 802.11b home network, and it should also work at most wireless hotspots, such as those provided by T-Mobile at most US Starbucks locations.

The Future of VoIP
I'm not alone in seeing VoIP (particularly when combined with wireless networking) as a truly revolutionary technology. Many hardware and software vendors are working on methods to include VoIP capabilities in their products. I recently learned that ViewSonic plans to include VoIP software with its V1100 Tablet PC.

One tip I can offer: All voice applications (including VoIP and speech recognition) work better with a headset than with the low-quality microphone and speakers built into most notebook and Tablet PCs. Voice applications, including both VoIP and speech recognition, are the first radically new and truly useful (not to mention money-saving) applications I've seen in many years. These technologies really work!

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