Weigh the pros and cons of VoIP over wireless

The next natural step in network convergence is the combination of VoIP and wireless networking technologies. While VoIP over wireless offers benefits, the technology isn't without drawbacks. Deb Shinder offers an overview of the advantages and challenges of VoIP over wireless.

Voice over IP (VoIP) technology allows companies to cut the Telco cord and make phone calls over the Internet. Now, with VoIP over wireless—also called VoW, VoWiFi, wVoIP, and a number of other acronyms—organizations can cut all the cords. Numerous vendors are offering Wi-Fi IP phones that operate on the same 802.11 technologies used for wireless networks.

According to a study from Infonetics Research, sales of Wi-Fi IP phones will likely reach $3.7 billion by 2009. The market already totaled more than $125 million in 2005, and it's growing steadily, particularly in business fields that have many mobile workers. That includes people who work in hospitals and factories, on sales floors, etc.

Major consumer-level networking equipment makers such as D-Link, NETGEAR, and Linksys are also getting into the act, selling IP phones that work with their Wi-Fi routers. Enterprise-class vendors make IP phones that work with business WLANs and IP PBX equipment. FierceMarkets hosted the Wireless VoIP Executive Summit in November 2006, which addressed present and future wireless VoIP technologies and issues.

Many technology analysts think the wave of the future will be dual-mode mobile phones, which can function as IP phones on a Wi-Fi network where one is available (be it home, office, or public hot spot) or use cellular technology in areas where there's no Wi-Fi network. Either way, the phone would have the same phone number. Because costs would be low when using Wi-Fi, such a device could replace the landline entirely for many users.

Is your organization ready for VoIP over wireless? Here's an overview of some of the technology's pros and cons.

Advantages of wireless VoIP

A big advantage of wireless VoIP is lower cost as compared to traditional cellular phone technology. Wi-Fi networks are already in place in many areas, and companies can deploy them quickly and inexpensively where they're not. People can use IP phones wherever an Internet connection is available, and VoIP call quality is rapidly improving—to the point where in many cases it's equal to or better than cellular.

If properly implemented and marketed, wireless VoIP could become as big a challenger to traditional cellular phones as wired VoIP is becoming to landlines. Major VoIP providers are already going wireless. For example, Skype recently added the ability to run its service on Windows Mobile devices.

Two big challenges

The concept sounds great: Combine the low cost of VoIP with the convenience of wireless networking. It's the logical next step in the move toward more cost-effective and mobile telephony. But there are a couple of major obstacles to implementation—reliability and security.

The reliability question

Most users are willing to tolerate some downtime and delays associated with computers and data networks. We don't expect to receive our e-mail messages instantly, and if network glitches result in a few minutes or even a few hours delay in delivery, we don't think too much about it.

When it comes to voice communications, however, the public switched telephone network (PSTN) system has spoiled us. We expect the phones to work—every time. We expect high-quality transmissions. And we expect the connection to stay connected until we choose to disconnect.

The reliability question is the biggest reason that organizations haven't adopted VoIP more quickly. Because it's a real-time application, VoIP is more sensitive to packet loss and other networking problems than most data-oriented applications.

And wireless technologies add another layer of things that can go wrong. RF interference, range limitations, weak signals, and the like can cause a VoIP call to break up or disconnect. Performance and quality problems with a VoIP-over-wireless connection can originate with the network/bandwidth, QoS configuration, or the endpoints (handset or call server).

But tools are available to help troubleshoot VoIP performance problems. For example, enterprises can use AirMagnet's VoFi Analyzer to validate and watch quality of service (QoS) and monitor VoIP calls end to end.

Security issues

Wireless security concerns have kept many companies from implementing 802.11 networks on their sites, and it's as much of an issue for VoIP as for other applications that transmit over wireless. Because the VoIP packets travel across the airwaves, it's easier for an intruder or attacker to intercept them as they move across the network.

The same security threats exist for wireless VoIP as for wired VoIP—and then some. The same security mechanisms used for wired VoIP—such as IPSec encryption to protect the confidentiality of packets at the network layer, TLS encryption to protect session initiation and secure call traffic at the session layer, and Secure RTP (SRTP) to encrypt the media at the application layer—are all applicable to wireless VoIP as well. But companies need to take additional steps to secure the wireless link itself.

To secure wireless VoIP, organizations need to establish the right policies, use the right security protocols, and select the right equipment. Here are some tips:

  • Policies should prohibit "rogue" access points and ensure the authentication and encryption of all VoIP calls using wireless channels.
  • Wireless encryption should not be Wired Equivalent Privacy (WEP), which has many known weaknesses, but a stronger wireless encryption method such as Wi-Fi Protected Access (WPA).
  • When selecting IP phones, use "hard phones" that are less prone to viruses and attacks than "soft phone" software installed on a regular PC operating system, and choose phones that support strong encryption.


The next natural step in network convergence is the combination of VoIP and wireless networking technologies, which have the potential to dramatically lower the cost of anywhere/anytime telephone service. While there are some obstacles to implementing wireless VoIP—primarily issues of reliability/performance and security—there are steps companies can take to improve performance, increase security, and make VoIP over wireless a viable option for your organization.

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Deb Shinder is a technology consultant, trainer, and writer who has authored a number of books on computer operating systems, networking, and security. She currently specializes in security issues and Microsoft products, and she has received Microsoft's Most Valuable Professional (MVP) status in Windows Server Security.

By Deb Shinder

Debra Littlejohn Shinder, MCSE, MVP is a technology consultant, trainer, and writer who has authored a number of books on computer operating systems, networking, and security. Deb is a tech editor, developmental editor, and contributor to over 20 add...