VoWLAN: Not Ready for Prime Time
September 23, 2003
Wireless VoIP has great potential, but there remain a few obstacles in its path to glory.
Whether the adoption of Wi-Fi in the enterprise drives growth of voice over wireless LANs (VoWLAN), or, as others contend, the interest in voice applications acts as a catalyst for the deployment of wireless networks, there are a number of challenges that must be met before voice over Wi-Fi goes mainstream.
That, at least, was the consensus among panelists at Monday's Wi-Fi VoIP Futures Summit at the VON tradeshow in Boston. VoWLAN deployments to date have been limited to niche vertical markets such as health care, retail and education, but as workers become increasingly mobile, it may make sense for mainstream enterprises to upgrade their phone systems, too. However, the word at the show was that VoWLAN won't see widespread adoption until certain technical hurdles are addressed.
The No. 1 hurdle is security. Most enterprises consider wireless security schemes such as WEP (Wireless Encryption Protocol) to be insufficient. "Basic WEP security is weak," said Alan Duric, senior system analyst for Global IP sound. "One insecure AP can expose the whole network."
The IEEE has yet to ratify the enhanced 802.11i security standard, so in the interim some vendors are using virtual LANs (VLAN) to isolate voice traffic on a separate network.
Virtual private networks (VPN) are also an option to enhance security, but are generally only available with softphones (software that adds voice capabilities to a PDA or laptop). Kam Toor, senior product manager at Cisco, said VPN services must be integrated into future Wi-Fi phones. Unfortunately, a VPN can introduce additional latency, which can negatively impact voice quality.
Voice quality is another issue entirely. Simply put, 802.11 networks were designed to carry data, not voice. There are no Quality of Service (QoS) mechanisms built into the standard that tell the network to prioritize voice packets over data, so a surge in network traffic could disrupt voice calls.
The upcoming 802.11e standard, which will add QoS to Wi-Fi, should help solve problems such as excessive packet loss and jitter (the variation of the arrival time of sequential packets). "Deployment of 802.11e will substantially improve the situation and help resolve a number of those issues," Duric said, but noted that it won't solve all the problems.
The ability to roam, both within Wi-Fi networks and from WLANs to wide area networks (WAN), is also a key challenge. Handoffs between access points need to be very fast -- less than 100 milliseconds, according to Cisco's Toor -- in order to have a clean voice call. That means authentication needs to happen quickly.
In addition, as users move between hotspots, particularly those with different service providers, or from a Wi-Fi to a cellular connection, they are issued a new IP address, making it difficult to keep up an established session, said Henrik Levkowetz, senior software developer at ipUnplugged. Mobile IP is one potential way to handle that problem, he said.
The standard allows users to keep a unique IP address even as they move across networks. "MIP goes thru NAT like a hot knife through butter," said Levkowetz.
On the plus side, Mobile IP gives users a fixed home address that they can always be reached at. However, Levkowetz conceded that handoffs aren't terribly fast; they range from 200 to 400 milliseconds. He said groups are working on faster handoff speeds.
Yet another concern is the battery life of the VoWLAN phones. Wi-Fi is a notorious battery drain, and the vendors agreed that Wi-Fi phones need to be more like cell phones in that respect for them to be successful. Cisco's Kam suggested that the battery in a Wi-Fi handset needs to provide at least three hours of talk time and 24 hours of standby.
Chipset makers are making strides on this front. Last week, Texas Instruments announced a low-power Wi-Fi chip for cell phones and PDAs. Motorola plans to use the chip in a combination Wi-Fi and cellular handset due out next year. Agere, meanwhile, unveiled a chipset earlier this summer that it says offers four hours of talk time and 60 hours of standby.
The final barrier, according to Boris Fridman, the COO of SoftJoys Labs, is interoperability. Current offerings are either proprietary or single vendor solutions. "It's exceedingly difficult to implement multi-vendor wireless voice in the enterprise," he said. "Any VoIP phone must work with any provider."
Despite these obstacles, the panelists remained enthusiastic about the potential for wireless VoIP. "If there are the right standards to address the challenges, there are tremendous opportunities," said Fridman.