Voice over Wi-Fi: no slam dunk; More integration work lies ahead to truly
unite VOIP and wireless LANs.
Business Communications Review, August 2005 v35 i8 p40(6)
Much fanfare has been made about conducting enterprise voice over IP (VOIP) calls over
802.11 wireless LANs, or Wi-Fi. To date, though, there has been far more discussion
than mainstream enterprise deployments of "Vo-Fi."
Just 18 percent of 419 enterprises surveyed in March by Webtorials, a Web-based
networking research and education firm, had deployed 802.11 phones or planned to
within six months (Figure 1). There are several reasons for the lukewarm adoption. One
is that many users are waiting for dualmode handsets and service plans from their cellular
service providers so that they can make both cell and Vo-Fi calls from the same device.
"Yes, I would like to do wireless VOIP," said Gary Bernstein, director, network and
communications services at McGill University in Montreal. "No, I have no imminent
plans to do so until my wireless network is fairly ubiquitous and [a carrier] can actually
show me a realistic business plan that involves dual-mode handsets."
Cellular service providers are gradually developing standards on which to base such
offerings, including those for fixed mobile convergence (FMC) like the ITU's IP
Multimedia Subsystem (IMS, see BCR, June 2005, pp. 18-23; also BCR, July 2005, pp.
52-57). But new standards on the enterprise side and more integration work are also
needed if Vo-Fi is to fulfill its promise. The 802.11 handsets will require the smarts of the
enterprise IP-PBX, and telephony applications will need to know what's going on in the
After all, the Wi-Fi portion of the network won't exist in a vacuum; it will need to
interoperate, from a calling feature and security perspective, with the rest of the
enterprise network, including the VOIP component. Wi-Fi and VOIP networks--and,
eventually, the cellular network, too--will require further integration and even perhaps
some mutually beneficial standards to achieve the following:
* Support those calling features of the IP-PBX that often inspire companies to choose
their PBX vendor in the first place.
* Enable E-911 applications to work from Wi-Fi handsets. This could otherwise become
a liability as E-911 gains an increasingly high profile at the state and federal levels.
* Fully support emerging presence-management applications.
* Allow the Vo-Fi network to optimize call routing and capacity planning.
To more closely integrate Wi-Fi and telephony systems and applications, industry
partnerships are starting to emerge, as shown in Table 1 and discussed in further detail
What's Been The Holdup?
Vo-Fi integration efforts have taken a back seat to more immediate technical wireless
LAN hurdles. The industry has been preoccupied with addressing security vulnerabilities
and centralized management architectures for scalability. And in terms of voice
specifically, the Wi-Fi industry is still ironing out important quality-of-service (QOS) and
roaming standards to assure reliable performance. It is also tackling power-consumption
and location tracking issues in Wi-Fi-enabled phones.
Better location tracking would be a boon to E-911 and other security efforts (see "E-911,
Vo-Fi and Workplace Safety," p. 42). At the same time, it would enhance the value of
presence and other location-centric applications. It could also lead to a common way to
share wireless location information with other applications.
At the Worcester Polytechnic Institute's Wireless LAN Research Lab (WLRL),
improving the accuracy of Wi-Fi location tracking is being worked out in concert with
the Wi-Fi industry.
"The Vo-Fi space is still far from stable," said Emmanuel Agu, WPI assistant professor of
computer science and WLRL member.
PBX And Wi-Fi Partners Work On Vo-Fi
In terms of feature support, most IP-PBX vendors are moving toward supporting Session
Initiation Protocol (SIP) on the line side, which is the connection from the PBX to the
phone. Depending on the number of proprietary enhancements IP-PBX makers add to
basic SIP, SIP-enabled handsets then would be able to interoperate with some IP-PBX
calling features, expanding users' mobile phone choices.
At the same time, IP-PBX makers are also working with at least one third-party handset
maker to customize an 802.11b handset to support their specialized calling features. For
example, as shown in Table 1, Alcatel, Avaya, Cisco, Nortel, Siemens and others have
worked with SpectraLink to build custom versions of SpectraLink NetLink Wireless
Alcatel, Avaya, Nortel and Siemens OEM the handsets and brand them as their own;
Cisco manufactures its own 802.11 handset (the Cisco 7920), as well, and offers users a
choice between Cisco- and SpectraLink-branded devices.
Some features of call servers from 3Com, Nortel and Avaya now also work on the
Research In Motion (RIM) BlackBerry 7270, which started shipping earlier this year. The
7270 is a traditional BlackBerry e-mail-centric device with an 802.11b connection in
place of a cellular connection. The BlackBerry 7270 interoperates with call servers that
support SIP-standard features on the line side of the network.
More sophisticated SIP features--call hold, call forward, call resume, conference calling,
for example--are in development for the BlackBerry 7270, according to RIM director of
product management Kevin Oerton. Adding a GSM radio to the 802.11b device for dual-
mode operation is about 18 months away, he said.
Avaya and Cisco softphone clients work on Symbol Technologies' Pocket PC-based
MC50 and MC9000 data-centric handheld devices, emulating the full feature set of
Avaya and Cisco IP-PBXs. And a generic dialer has been integrated into the Microsoft
Windows CE mobile operating system that provides basic SIP calling features such as
voice mail and call transfer. However, advanced calling features, such as three-way
calling, are more likely to be available with softphone clients developed by the IP-PBX
Another potential drawback to generic SIP phones might be the need for separate
management tools to set up and administer them, noted Ben Guderian, vice president of
market strategies and industry relations at SpectraLink. "But administrators would really
like a standard set of best practices," he said.
Partners And Others Tackle Handset Location
Besides coordinating to develop Vo-Fi handsets, the PBX and Wi-Fi partners and other
vendors are also working on ways to get wireless location information to E-911, presence
and other applications. Cisco, for example, introduced its 2700 Location Appliance in
the spring, which supports an XML API and scales to track several thousand Wi-Fi
A location appliance is a specialized device that collects signal strength and distance
information between wireless clients and access points, then uses special algorithms to
calculate the client's location based on that data. Other location appliance makers include
AeroScout, Ekahau and Newbury Networks.
"We have discussions going on with our telephony folks about integrating our own
wireless LAN location information [with Cisco Emergency Responder, Cisco's E-911
application]," said Pat Calhoun, chief technology officer in Cisco's wireless
networking business unit.
From an applications feature perspective, he added that the company has had an XML
parser in field trials on its 802.11 handsets, which will soon allow many of the XML-
based applications already available from 300 active third-party developers for Cisco's
wired VOIP phones to port over to the company's Vo-Fi handsets.
For example, in the health care environment, patient monitoring information can be
delivered directly to nurses' handsets, said Steve Toteda, senior manager, mobility
solutions and client devices at Cisco. For mainstream users, the Cisco 7920 handset
gained XML-based access to corporate calendars and searchable directories in June.
Siemens, which acquired Wi-Fi startup Chantry Networks late last year, said it has a
partnership with Newbury Networks to integrate location tracking into its portfolio. "We
don't yet have a customer willing to pay for sensors [dedicated devices collecting location
data]," said Shawn Sweeney, director of technical marketing in Siemens' wireless LAN
group. "We're working out how to make location information available to the PBX in a
meaningful way for telephony-centric applications and call routing," he said.
The closest thing today to an industry standard for collecting and presenting Wi-Fi
location information is an optional component to the emerging IEEE 802.11k extension
for radio resource management, which is in the letter ballot phase. The option is a MAC-
level enhancement enabling a Wi-Fi station to send a location request to an access point
asking that the AP tell the client where the AP is and, in turn, asking the AP to locate the
"This is in the form of a frame request and a frame response with latitude and
longitude, and it is being driven by VOIP," said Richard Barnwell, chief technology
officer at PanGo Networks, a company specializing in wireless location tracking.
"But getting location information to IP-PBXs or applications, such as element
network management systems, is not standardized at all now."
Whose APIs To Use?
While most agree that a standard interface for location information would be valuable, it
doesn't appear that one is in development in a standards body. Instead, vendors are
working to extend their own application program interfaces (APIs).
"We develop the API between our wireless LAN and each IP-PBX manufacturer's
product," noted Kamal Anand, vice president of marketing at wireless LAN systems-
maker Meru Networks. "But we'd prefer not to do it in custom format for everyone."
Ram Ramaprasad, director of product line management at IP-PBX maker 3Com, agreed.
"We need to create a standard software format or protocol for location information
presentation so that any application can use it," he said. 3Com is a development partner
of wireless LAN maker Trapeze Networks. "If we work only with Trapeze [on Wi-
Fi/telephony integration]," Ramaprasad said, "we need to tell customers who use
someone else's wireless LAN that they won't be able to use our E-911 application."
To that end, Symbol Technologies is attempting to create a set of complete APIs for any
location engine interfacing to various wireless location-tracking vehicles, including
802.11 and radio frequency identification (RFID), revealed Alan Marcus, vice president
of marketing in Symbol's wireless infrastructure division. Symbol would then open up the
APIs for public use, he said.
"We've started those conversations with favorable results," Marcus said. For now,
Symbol partners with location appliance vendor Ekahau, which, in turn, interfaces to
upstream devices and applications that use its API.
In the meantime, PanGo has created location middleware called PanOS that feeds
location information to Wi-Fi location appliances or controllers as event streams.
Application developers can use the data regardless of which wireless network type
resides behind the appliance. PanOS interfaces with the Cisco 2700, for example,
and other Wi-Fi vendors are considering writing their own adapters for PanOS this
year, according to Barnwell.
Gaining A Presence
Location information from wireless LANs could add value to presence applications,
which today typically offer individuals' identity and availability information, along with
their preferred way of communicating. Part of the goal of presence is to streamline
business communications by avoiding phone tag and getting important calls to people at
the right time. Other applications are expected to emerge as the capability evolves.
In hospitals, for example, so-called "rich presence" could be used to alert the appropriate
specialist to an emergency--such as a cardiologist, should a patient experience a heart
attack. This could eliminate the need for "code blue" public address announcements,
according to Phil Edholm, chief technology officer in Nortel's enterprise business unit. "If
there is an emergency, the system can make the decision about who to contact based on
staff skill sets as well as their location and availability," he explained.
Similarly, said Meru's Anand, business users might set policies about their availability
based on location. "Once you have the coordinates, you might have a policy that if you're
in a meeting, don't ring, but send me a message or beep in a different way."
The IP-PBX--or whatever kind of multimedia communications server it morphs into--
must contain the intelligence to make these decisions and interact with the mobile
handset appropriately, based on policy, said Dan Simone, chief technology officer at
In this spirit, Trapeze's partner, 3Com, said the next stage for its VCX IP-PBX, in terms
of feature support on the RIM BlackBerry 7270, is a soft client with VCX presence and
conferencing capabilities. Ramaprasad added that 3Com also intends to provide a PBX
soft client to a Nokia dual-mode phone, to ship later this year.
In addition, Nokia said in June that it intends to license Cisco technology to integrate
Cisco Call-Manager IP-PBX features into its dual-mode Nokia Series 60 devices over
Call Routing And Capacity Planning
Resource-based call admission control is another important reason to improve linkages
between IP-PBXs and wireless LANs, particularly because the wireless access network is
susceptible to variations in resource utilization.
"There are lots of things you can do with the wireless LAN infrastructure and IP-PBX to
provide better services under load," said Cisco's Toteda. "If all employees come from
satellite offices to headquarters for a meeting, they must be accommodated in terms of
capacity planning. We're working on that now, and that involves both the back-end IP-
PBX and the wireless LAN."
Also, without signaling among handsets, the wireless LAN and the IP-PBX, the PBX
won't know whether to let the call onto the network or to send back a "busy" signal.
Today, such signaling is accomplished using SpectraLink's proprietary technology in
most Vo-Fi networks.
"It's pretty important that the information in the wireless infrastructure should be used to
improve the performance and quality of calls," said Meru's Anand.
For example, the monitoring capabilities in the wireless LAN access point could signal
the client or the IP-PBX that the quality of the airwaves is degrading so that, based on
policy, the device or application can then decide whether to continue a call or attempt to
move it into an area with a better signal.
"Through APIs, we provide that information to an IP-PBX or SIP server," said Anand.
He added that in Japan, PBX manufacturers Fujitsu, OKI and Hitachi have used Meru to
implement these types of applications in customer networks, and that Meru is working
with a large U.S.-based PBX maker to do the same.
For further call control, Nortel's Edholm suggested that it might be possible to integrate
Wi-Fi capacity information with IP-PBX software to create a "camp-on" feature or one
that diverts the call to the wireless WAN, in cases where the user is carrying a dual-mode
handset, with associated rules as to when to allow the WAN alternative (see "Call
Handoffs Between Vo-Fi And Cell Networks," p. 44).
For Vo-Fi to be fully embraced by mainstream enterprise users, not only must wireless
QOS and roaming standards mature, but information about the status of the RF network
and the location of mobile devices must become better integrated with telephony
applications. In addition, IP-PBX calling features--wherever they are hosted--must easily
port to 802.11-capable handsets of the user's choice, including emerging dual-mode Wi-
Because of this last requirement and given the apparent blended destiny of Wi-Fi and
cellular networks, some believe that the future of the enterprise PBX as we know it is in
jeopardy. SIP is the glue expected to be used to mix and match features and handsets
across the LAN-WAN boundary, and a pure SIP model is a peer-to-peer, softphone
model, where the PBX simply "gets out of the way," said Dave Juitt, CTO at wireless
LAN company Bluesocket.
In fact, SpectraLink's Guderian called SIP "the great equalizer" because it offers globally
unique addressing and a common feature set. He and Juitt believe that SIP eventually will
allow users to take a single handset from their office to home to another company and to
"But there is still SIP engineering that needs to be done in handsets; the protocols aren't
yet fully mature," Juitt concluded
Companies Mentioned In This Article
3Com Corp. (www.3com.com)
Aruba Wireless Networks (www.arubanetworks.com)
Cisco Systems (www.cisco.com)
Colubris Networks (www.colubris.com)
Meru Networks (www.merunetworks.com)
Newbury Networks (www.newburynetworks.com)
PanGo Networks (www.pangonetworks.com)
Research in Motion (www.rim.net)
Siemens AG (www.siemens.com)
SpectraLink Corp. (www.spectralink.com)
Symbol Technologies (www.symbol.com)
Trapeze Networks (www.trapezenetworks.com)
Worcester Polytechnic Institute (www.wpi.edu)
Joanie Wexler is an independent editor and writer based in Silicon Valley. She has spent
most of her career writing about trends in the IT and computer-networking industries.