Voice telephony over wireless LANs comes at a price
Many organisations with plans for IP telephony and WLANs may think that their next move is to support voice calls over these networks. They hope to reap the rewards of a converged infrastructure and added mobility. But there's a price attached to getting voice-over-WLAN capability: infrastructure costs can rise significantly, as a much more complex network is needed to support voice calls throughout an office.
Organisations must carefully evaluate whether the potential benefits of IP telephony via WLAN outweigh the extra cost. The following six sections outline the main issues.
Technological standards
The current lack of a technological standard for voice-over-WLAN equipment is one factor that limits uptake to certain industry applications. The relevant standard, called 802.11e, is still being developed by the Institute of Electrical and Electronics Engineers (IEEE) and pays particular attention to QOS for voice calls. It has two components -- Wi-Fi Scheduled Media (WSM) and Wireless Media Extensions (WME) -- the latter especially important for business use.
Equipment based on this standard is expected to reach the market in the second half of 2005, from a wide range of vendors. The Wi-Fi Alliance will certify equipment that meets its requirements for interoperability, but vendors are likely to introduce proprietary innovations to improve performance and add features.
Quality of service
QOS is critical for voice calls, but the limited range and capacity of WLANs imposes difficulties not found in wired LANs. An important issue concerns the handoff between access points in office WLANs, which is sometimes delayed. These delays can severely disrupt voice calls.
Vendors already offer proprietary QOS support within their WLAN products, but this situation severely limits interoperability between different makes of access point and handset. Also, as noted above, though 802.11e will improve interoperability, proprietary features are likely to remain.
Handsets
Until 802.11e equipment arrives, customers wanting to transmit voice calls over WLANs have little choice but to buy expensive proprietary handsets. These cost from $400 (£219) to $600 or more in the first half of 2004, and, though prices are falling, it's doubtful whether they will drop below $200 for several years. However, there is one possible alternative to overpriced proprietary handsets: PDA softphones. These are less expensive, but buyers need to check that battery life is sufficient.
