January 28, 2004
Technology in Focus features analysis of recent technology news articles, by the consultants in Technology Group, IDA. This is the top pick of the month from a list of 10-20 news analysis compiled monthly.
VoIP should make wireless carriers nervous, Mobile Pipeline, 18 Dec 2003
by Steven Ong, Consultant, ENAT
VoWLAN or Voice over Wireless Local Area Network basically expands the capability of Wireless LANs. While Wireless LANs are usually used for data connectivity using mobile internet protocol, VoWLAN allows for voice to be transmitted over the Internet. VoWLAN however has its own unique QoS (quality of service) challenges relating to fluctuating wireless throughput and roaming among AP (access points). Products currently in the market constitute mainly of proprietary wireless network hardware and software.
Basically, VoWLAN systems work in two different ways. Calls made from a wireless phone product from SpectraLink, Symbol, and Cisco are routed from the phone to a WLAN access point (AP) and then to a VoIP gateway. The calls are then translated between the IP network and the private branch exchange (PBX). This set-up allows all regular PBX functions that are available on a worker's wired desk phone to be available on the VoWLAN phones. Calls that are made to phones outside the company will go through the PBX to the PSTN (Public Switched Telephone Network).
Another way for VoWLAN to work is for software-based phone, also known as softphones, to route calls over the Internet. In this scenario, users can use the softphone on their PDA or laptop to place calls from a location or hotspot that offers a WLAN. The call could be routed anywhere over the Internet thereby making it virtually free.
However, like any voice call that uses the Internet, users can't control the quality of the connection. Even over the local network, VoWLAN has its shortcomings. The 802.11 standards, including those that cover QoS, security, and roaming simply weren't designed to support voice. As it is, no special priority is given to voice, so when traffic spikes on the network, dropouts may occur. This is compounded by the need for channel security, where encryption and authentication must happen fast enough so that a call isn't dropped or degraded when a user moves from the coverage area of one AP to the next. Also, an 802.11b AP is capable of running only three uncompressed audio streams smoothly so there are finite resources in terms of channel and frequency.
VoWLAN vendors themselves have admitted that the existing 802.11 standard can't support handoff fast enough and neither can the security solutions developed by most gateway vendors. Even 802.1x, the upgraded security standard in development, won't work quickly enough. The handoff between APs needs to be under 50 milliseconds to cleanly support a voice call that allows the user to roam between APs. The IEEE is working on 802.11e, a QoS standard that should be finalized next year. In the meantime, vendors like Symbol and SpectraLink have implemented their own proprietary QoS mechanisms through their hardware.
In short with the existing solutions, VoWLAN may not be robust and reliable enough to support enterprise deployment for a large base of users. It is also not practical for public hotspot operators to mandate the use of a particular QoS method for the radio chip/card used by its customers. The situation is however improving and the impending rectification of 802.11e should address most of the above issues. Given the potential, wireless operators should seriously start looking at ways to tap VoWLAN to complement their existing cellular network services.
Some words about the writer
Steven Ong is a consultant with the Technology Group, tasked with the responsibility of identifying, tracking and exploring leading edge enabler technologies in the mobile wireless arena. He is currently looking at areas such as Digital Rights Management, wireless security as well as mobile platforms.
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