VOICE
NETWORKS

From the April 2005  issue of Communications News

Beyond the cordless phone

Adoption of voice on wireless LANs is the next logical step.

by Tracy Venters

Combining the benefits of wireless LANs (WLAN)–namely, the potential to access the network from any device anywhere–with the benefits of voice over IP (VoIP)–free or reduced rate calling–seems to be a match made in heaven. With WLANs, users can cut the umbilical cord for their data applications. With voice over WLAN (VoWLAN), users can do the same for their voice applications.

The most obvious benefit of VoWLAN is the same benefit offered by VoIP. In an enterprise environment, voice can ride for free on the existing data network. This principle naturally extends to the wireless LAN. Users can utilize VoIP from a desktop phone, a softphone client on their laptop or PDA, or from a wireless handset supporting VoIP. Not only is VoWLAN cheaper, it can also offer better coverage indoors and better voice quality than cellular.

Furthermore, the VoWLAN phone can be integrated with the enterprise PBX. Integration with the PBX allows calls to be placed to and received from the PSTN, and also supports PBX features, such as call forwarding, messaging and conferencing.

Despite the benefits, there are many obstacles to successful VoWLAN deployment. The technical obstacles are perhaps easier to overcome, with many of the shortcomings already being addressed by manufacturers and in the standards bodies.

For example, the IEEE has ratified the long-awaited 802.11i standard to enhance Wi-Fi security. Although the standard has been in the works for years to replace the flawed wired equivalent privacy (WEP) originally defined in 802.11, the industry had already settled on a de facto upgrade to WEP known as Wi-Fi protected access (WPA). WPA offers many improvements over WEP, such as authentication and stronger encryption. 802.11i (known as WPA2) also offers government-grade encryption through the advanced encryption standard (AES).

There is a potential downside to the more secure WLAN provided by 802.11i. Security adds latency, which could prove unacceptable to VoWLAN, leading to dropped connections while roaming. In mid-2004, the 802.11r working group was formed to address the issue of faster roaming. Some people, however, contend that the combination of pre-authentification supported by 802.11i, along with improvements in radio resource management supported in the upcoming 802.11k, will be enough to keep the handoff under 50 ms, the generally accepted benchmark for voice applications.

Quality of service (QoS) is another area where the standards bodies have moved at a snail’s pace, forcing interim solutions to be adopted by industry. Moving closer to a true standard is the Wi-Fi Alliances’ wireless multimedia (WMM)–the wireless multimedia extension (WME) part of the upcoming 802.11e standard–for which the alliance currently provides certification. WME prioritizes traffic into different classes, with higher priority given to voice.

The full 802.11e specification also calls for support for wireless scheduled multimedia (WSM), which allows applications to reserve or “schedule” bandwidth. Scheduling bandwidth has an added benefit, allowing devices to reserve power during periods when they are not scheduled to transmit data. This is important because VoWLAN handsets have typically suffered from limited battery life compared to cell phones.

Despite these technical obstacles, the most difficult aspect to the introduction of VoWLAN technology is that enterprise users like the convenience offered by their cell phones (some analysts estimate that as many as 60% of a worker’s cellular calls are made while in the building or within range of the company WLAN). Access to PBX features such as extension dialing is not enough to convince most users to carry around two wireless phones. Dual-mode phones, however, supporting seamless roaming between WLAN and cellular networks, can provide users the convenience they desire, while saving corporations the expense of on-campus cellular minutes.

Solutions for WLAN/cellular roaming exist today, although they are, for the most part, proprietary. Several vendors are working to standardize the solution through the industry consortium SCCAN (www.sccan.org).

Most of the early adopters of VoWLAN have been in the areas of healthcare, manufacturing or education. These industries have at least one common thread: users whose duties require them to roam large campus environments throughout the day. For healthcare, Wi-Fi handsets have an added appeal, since cell phone use in hospitals is often prohibited due to its interference with patient care equipment.

Many colleges and universities now provide wireless devices such as PDAs and laptops to all new students. In many schools, close to 100% of the population already has a personal cell phone. Allowing students to phone home via the WLAN can be a differentiator over competing schools.

In the end, VoWLAN is really just another means to access a VoIP service. Users will come to expect it and they will be no more willing to pay a premium for it than they would be to pay extra to use a cordless phone on a wireline. They will, however, be more inclined to pay for the additional functionality VoWLAN provides.

Location tracking is one such capability. The Wi-Fi network can be used to track the location of a Wi-Fi client, which, combined with VoWLAN, opens up a plethora of new applications. For example, not only does this provide university students a cheap way to phone home, it can provide security guards with a student’s location in case of an emergency.

This technology can also be used in the enterprise to intelligently route a call to a worker based on her location. For example, a user may prefer to have calls routed to his desk phone while in the office, to voice mail while in a conference room, and to a wireless handset while anywhere else. The network automatically tracks the user based on the location of the wireless handset. Outbound calls can be intelligently routed, as well. When a user calls to report a malfunctioning projector in a conference room, for example, the maintenance department automatically receives the location.

For more information from tekVizion:
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Tracy Venters is with tekVizion, a systems integrator for the telecommunications industry based in Richardson, Texas.