Voice over IP goes wireless: VoIP promises great cost savings, but quality of service and security are still issues to consider.

INTERNET PROTOCOL (IP) IS LEAVING its mark on telephony. A handful of wholesale phone companies are breaking your voice into syllable-sized packets and sending it over a lattice of wireless networks that resemble, and include, the Internet. Why? To help businesses avoid the long-distance charges that come with using traditional telephone networks.

Businesses that stand to benefit most from wireless Voice over IP (VoIP) are those with remote employees (who run up large phone bills in voice and fax calls to company offices and usually require an additional phone line at the company's expense) and multiple offices with high voice traffic. If remote employees or offices are in multiple states or countries, the potential for cost reduction is even stronger.

In VoIP systems, analog voice signals are digitized and transmitted as a stream of packets over a digital data network. The network can be wired or landline (the basic technology remains the same), but for this article, I'll focus on wireless networks.

IP networks let each packet independently find the most efficient path to the intended destination. The packets mar arrive out of sequence, or possibly not at all. At the destination, however, the packets are re-assembled and converted back to the original voice signal. Ideally, VoIP technology ensures proper reconstruction of the voice signals, compensating for echoes, jitter, and dropped packets.

Anatomy of a wireless VoIP connection

Historically, telephone calls were made through the public switched telephone network (PSTN). VoIP gateways provide a bridge between the local PSTN and the IP network for the originating and terminating sides of a call. VoIP technology translates the destination wireless telephone number into the wireless data network address (IP address) associated with a corresponding terminating gateway nearest to the destination number. The terminating gateway initiates a call to the destination phone number to establish two-way communications. Despite the extra connections, the overall call set-up time isn't much longer than with a call fully supported by the PSTN.

The IP network can be a proprietary wireless network, a wireless network of leased facilities, or even the Internet. The Internet is the least expensive option; but, because it lacks any central administrative entity, it's subject to congestion and temporary outages. You can get more reliable communication, albeit at a higher price, via dedicated wireless networks.

VoIP cost structure

Local telephone companies impose access charges to let long distance carriers originate or terminate the local portion of each wireless telephone call. In the U.S., however, the Federal Communications Commission has ruled that such access charges don't apply to VoIP calls. Transmission costs associated with the long distance transmission are typically much less, due to the reduced bandwidth required by the data packets associated with the call. In addition, the settlement charges associated with international calls don't apply when an IP network carries the international transmission.

A PSTN-supported call requires an end-to-end circuit that's maintained for the duration of the call. A VoIP call, by contrast, involves the transmission of many individual packets over an IP network. So, the cost of a VoIP call depends in part on the number and size of the packets transmitted (the bandwidth required). Speech compression algorithms can reduce the required bandwidth by a factor of eight or more. You reduce bandwidth even more with software that recognizes the silences that naturally occur in human speech and explicitly doesn't transmit them.

So, the total cost per VoIP call is a result of the costs associated with access to the gateways at both ends and the cost of transmission over the IP network. If you're accessing the VoIP gateway at either end of the call through the PSTN, you must consider the costs of local or long distance connections (or, perhaps, the monthly cost of a toll-free access number).

TIP: Depending on the location of the gateway and the destination number, long distance charges may apply. You'll want the terminating gateway to be at the location that gives you the best long-distance rate possible. You can implement least-cost routing algorithms to ensure the lowest end-to-end rate.

VoIP in action

Many mobile users make long distance calls on a regular basis. Take a mobile user from Maryland, who makes calls every month to her home office in New Mexico; U.S. clients in Pennsylvania and New York; and international clients as far away as Australia and Malaysia. By using VoIP, the mobile caller from Maryland estimates she's saving about US$60 per month. The cost is zero for domestic calls in all 50 states. On average, mobile users can save 20 to 60 percent on phone bills, depending on the route the phone companies take when they use the IP carriers to deliver their international calls rather than PSTN carriers.

What's the catch?

Although the technology is improving, VoIP calls aren't nearly as clear as telephone calls. Expect intermittent static, echoes, and broken-up conversations. Sometimes, it might be difficult to connect at all. Because of such annoyances and the lower cost of local calls, VoIP services probably aren't yet a good fit unless you're calling internationally or calling colleagues within your own company. It isn't a perfect connection, but certainly good enough for basic conversations.

With guaranteed bandwidth availability and manageable quality of service (QoS), a dedicated wireless network provides a more stable and high-performance medium than the Internet. The 802.11e (Wi-Fi) standard focuses on the QoS and multi-media support that will make VoIP a viable solution for businesses wanting to cut costs.

Remember, this evolving technology. There are security vulnerabilities you must consider before making any decisions. (See the sidebar discussing some of the security vulnerabilities found in VoIP wireless phones.)

Toward converged networks

Although most people think VoIP's primary benefit is its ability to reduce phone charges, the real key is the integration of voice and data communications. The consensus is that most small businesses and enterprises will take a phased approach to converging wireless data and voice networks. The dramatic "throw out the PBX and replace every phone with an IP phone" scenario isn't a likely one.

One of the tremendous benefits (and a source of confusion) when building the converged wireless network, is that there are a number of equally

valid places to begin. For many companies, installing an open-platform PBX at small, remote offices is the optimal starting point. For others, it might be linking PBX and Microsoft directories at the back end or integrating voice mail and e-mail systems for flexible message delivery.

For many organizations, the traditional PBX will co-exist with the newer VoIP services for some time. While the costs associated with operating and maintaining a converged VoIP wireless network are comparable to that of running a PBX, the additional cost of products required to deploy VoIP is a roadblock to some companies.

One of the long-term goals of Internet telephony is to not be restricted to any one kind of device. In the future, the mobile user will be able to use wireless handheld organizers and laptops for Internet calls. Moreover, these devices will integrate voice, video, and speech recognition technologies.

MOBILE BUSINESS BENEFITS

Because packet-based networks provide a high cost-benefit ratio compared to traditional telephone networks, an increasing number of businesses are transporting voice calls over IP networks to avoid long-distance charges. As the 802.11e standard increases the quality of service over wireless LANs, VoIP becomes even more tempting for cost-conscious companies.

RELATED ARTICLE: Wireless VoIP phone security issues.

More than a dozen security vulnerabilities have been found in one of the most popular models of VoIP wireless phones, some of which have consequences that reach beyond the telephony infrastructure. The VoIP wireless phones often ship without a password for the administrator account, which carries an unchangeable generic username of "admin." If the user doesn't set a password, an attacker with physical access to the phone ca n easily set the password, giving himself administrative access to the phone. A remote mobile attacker can perform this same task using the phone's Web user management interface. The attacker can then remotely log in using the phone's Telnet server. He can then use the VoIP wireless phone as a fully Portable Operating System interface for a UNIX (POSIX)--compliant network device with storage space, bandwidth, and a CPU.

Another vulnerability is the Session Initiation Protocol (SIP), a protocol for initiating interactive user sessions that involve multimedia elements such as video, voice, and chat. Because SIP is built on the IP protocol, SIP-based VoIP wireless phones are also susceptible to well-known IP attacks. For example, an attacker with administrative access can launch a denial-of-service attack against a VoIP wireless phone by changing the SIP listening ports (requiring authentication of incoming calls--in which case, neither the caller nor the recipient is notified if the authentication fails). Also, because the Web user interface is only protected by a base64-encoded username and password pairs, anyone sniffing traffic between the Web interface and a phone can see the login information in what's essentially clear text.

For more information about VoIP equipment and software, subscribers can read and extended version of this article at http://Advisor.com/doc/11547.

John Vacca is an information technology consultant and internationally known author based in Pomeroy, Ohio. Since 1982, John has authored 37 books and more than 443 articles in the areas of advanced storage, computer security, and aerospace technology. John was a configuration management specialist, computer specialist, and the computer security official for NASA's space station program (Freedom) and the International Space Station Program, from 1988 until his early retirement from NASA in 1995. John was also one of the security consultants for the MGM movie titled "AntiTrust," released January [e-mail].