When most people think of wireless LANs, they generally only consider transferring data while using applications such as a Web browser, e-mail client, for file transfer, etc. It's possible, however, to use a wireless LAN as the transport system for carrying telephone traffic from mobile users as well. Voice over Wireless LANs (VoWLANs) are beginning to proliferate.

Applications and Benefits
A significant benefit of mixing telephone traffic with data on a wireless LAN is to provide mobility and make use of a common infrastructure. The support of a common system for both data and voice traffic is generally simpler and less expensive than two separate entities.

For example, many warehouses utilize two-way radios operating in licensed frequencies to provide communications among clerks and supervisors. Mobile communication is needed in this environment due to nomadic users and the large size of the facilities. In many cases, warehouses utilize wireless LANs for providing wireless data collection in inventory and shipping/receiving applications. By using mobile phones designed to interface with the wireless LAN, a warehouse can avoid the need for two-way radios and the corresponding operational management functions.

The use of wireless LAN phones within the offices of an enterprise is compelling as well. In this case, a company can avoid the need to wire and rewire telephone outlets as the company size shifts. In fact, users could utilize an 802.11 phone to make very inexpensive long distant phone calls through the Internet.

Key Components
In addition to a wireless LAN backbone consisting of access points and a distribution system, a key component for implementing voice over wireless LANs is a telephone equipped with an 802.11 radio. The primary players in this market are Symbol and Spectralink, which have partnered with private branch exchange (PBX) vendors to sell their products. These phones, however, are somewhat pricey at about $500 each.

A company called Telesym has software that turn a PocketPC-based personal digital assistant (PDA) into a telephone. This can be a less expensive alternative if you already have PDAs on site. In addition, you only need to carry one device for multiple purposes.

Most voice over wireless LAN systems also requires a gateway or access point enhanced to handled to handle special bandwidth control requirements of voice traffic. For example, SpectraLink's gateway allows the phones to work with Cisco's Call Manager IP phone. The gateways will add cost to the system if you plan to effectively support voice traffic.

Despite these costs, however, an 802.11-based phone system is generally less expensive to install and support than a wired system. Of course you'll need to pay specific attention to the potential problems from wireless LANs, such as radio frequency (RF) interference and denial of service attacks.

Performance Requirements
Performance should be your primary consideration when installing a wireless LAN system that supports voice. 802.11b is only capable of running three uncompressed audio streams smoothly. As a result, it's important that the system compress the audio signals before transmission in order to increase the number of supported audio streams.

Another way to increase the number of audio streams is to utilize a higher performing standard, such as 802.11g or 802.11a for the wireless LAN backbone. 802.11a, for example, has the capacity to handle approximately four times as much voice traffic as 802.11b. The problem with 802.11a, though, is that other non-voice users of the network may only be equipped with 802.11b/g. As a result, consider installing access points that include both 802.11a (for voice users) and 802.11b/g (for data users).