Wireless VoIP works, but it’s work

Whole different animal than data-only WLANs, early adopters say

Large-scale deployments of VoIP over WLANs require careful thinking and planning, and attention to lots of details.

A trio of healthcare organizations say that large-scale wireless VoIP deployments work. But it takes work, and lots of it.

For years, wireless LAN vendors have touted voice calls over an 802.11 wireless net as a surefire hit in the enterprise market, creating the equivalent of cell phone mobility within the four walls of the enterprise or over a campus. The claim was that enterprises would simply leverage their migration to VoIP on the one hand and their deployment of wall-to-wall WLAN coverage on the other.

How to manage VoIP over WLAN

But most early wireless VoIP deployments, at least the public ones, have been modest, with a few hundred mobile handsets at most. Several vendors contacted for this story said they didn’t have any customers with 500 or more clients, the minimum threshold for this article. Others said they had some or a few, but none who would talk with us.

“For customers going down this path, they need to choose products that have been interoperability-tested,” says Joseph Fearday, telecommunications manager, Trinity Health, a Roman Catholic healthcare net of 45 hospitals, headquartered in Novi, Mich. “It’s not all going to fall from the sky.”

Wireless VoIP is still a systems integration project, typically involving the WLAN vendor, a PBX/VoIP vendor and specialized wireless VoIP vendors like Polycom’s SpectraLink and Vocera Communications, which offer client handsets, server software and proprietary protocols to make the whole thing work. The other major infrastructure vendor is Cisco; others like 3Com offer wireless VoIP phones.

Vendors are partnering more to simplify all this. Network companies like Nortel, for example, expand support even as they cut rebranding deals to tie their IP PBX product lines into, in this case, the SpectraLink products. Wireless VoIP vendors have set up sophisticated interoperability testing and certification of the various third-party components.

At St. Joseph Mercy Health System, in Novi, 600 SpectraLink/Avaya mobile handsets (including 300 in the past six months) are integrated with an Avaya IP PBX via a net of about 500 Cisco Aironet 1200 WLAN access points.

Fearday relied on SpectraLink’s interoperability testing program to ensure the various elements, including Avaya’s SpectraLink integration code, worked smoothly together.

Unforgiving voice traffic

WLANs that support large-scale voice nets are different from those that support only data, these network professionals say. File transfers can slow or experience jitter and the result will be barely noticeable delays. Not so with voice. “People will not tolerate choppiness in voice calls,” says Fernando Martinez, technology and data security officer for North Broward Hospital District (NBHD), a system of five hospitals in and around Fort Lauderdale.

NBHD has over 800 wearable Vocera wireless VoIP phones, running on a distributed WLAN of over 200 Cisco 1200 access points. Martinez deployed a wireless VoIP system about half that size at his previous job, as CIO of Miami’s Mercy Hospital. “The requirement for resilience, for a sustained stream of data, is very important in wireless VoIP,” he says. “Voice is not a forgiving traffic pattern.”

To compensate, more access points may have to be deployed, or deployed in areas that usually are not covered in a pure data net, such as stairwells or elevator shafts. Instead of the conventional omni-directional antenna for an access point, a directional antenna might be needed to focus the radio signal in a given area.

In these deployments, traffic types are divided between the two Wi-Fi bands. The 2.4-GHz band for 802.11b and 11g traffic is often set aside for voice clients, with data clients shifted to a pervasive 802.11a net in the 5-GHz band. That’s partly because many wireless VoIP devices only run in the 2.4-GHz band.

But the 2.4-GHz band has only three nonoverlapping channels, with each access point being able to use only one of the three. Where more than three access points are close together, it can be hard to keep the three channels clear. Martinez in the past has juggled the power settings on access points, in effect shrinking the reach of the radio. With each access point taking up less space, more of them can be put into a given area, while balancing the three channels.

Large-scale configuring

In large-scale nets with older access points like the Cisco 1200, this manual configuring becomes a burden. WakeMed Health and Hospitals, a 872-bed hospital in Raleigh, N.C., upgraded from an older pre-802.11 WLAN to a controller-based WLAN from Aruba Networks in 2005. Over 700 Aruba thin access points are distributed in 14 buildings in Wake County, with nine Aruba controllers. About 350 wireless phones are linked to the “nurse call” system, which has streamlined voice communications between patients and nurses, and among nurses and physicians. Another 300 phones are used by doctors, IT staff, administrators and facilities personnel.

WakeMed chose Aruba in part because of its automated WLAN channel, power and radio management features, says John Tuman, director of network services for the hospital. In the past, a group of client phones and data devices around a nurse’s station would automatically connect to the “loudest” access point. With automated features in the Aruba controller, those devices can be shifted to other nearby access points to optimize overall performance.

WakeMed’s wireless VoIP system is supplied by Nortel, based on SpectraLink phones and software integrated with the Nortel IP PBX line. The new system replaced Nortel Companion, an aging radio-based wireless voice system. In early 2005 WakeMed tested the Nortel/SpectraLink phones for performance and voice quality on Aruba access points that were also handling big file transfers between wireless laptops. Despite the congestion, the phones quickly associated to the access point, completed the call set-up to the PBX and delivered excellent voice quality, Tuman says.

None of the three sites has experienced overcrowding of VoIP calls on its access points, which would cause calls to be dropped. All report excellent voice quality, and all say they’ve received no complaints from users about it.

Having an effective WLAN management framework is essential in large nets, according to these users. Martinez is moving ahead quickly to upgrade the Cisco 1200 WLAN to a controller-based WLAN architecture for just this reason. “Without that, you’re limited as to how well you can fine-tune and optimize what you have,” he says. If someone reports a Vocera unit “going red” — losing it’s signal, you want to know quickly whether it was because the user was out of range of the access point, or because of interference or some other reason.

Don’t forget support, maintenance

Support and maintenance for the wireless VoIP net poses specific challenges. At WakeMed, for example, the autoconfiguring WLAN contrasts with the manual configuration needed for every SpectraLink phone. “This is an area for improvement,” says Tuman.

Martinez has found that his users need a fair amount of training to work the Vocera unit properly. The compact Vocera unit is designed to hang around the neck, for completely hands-free operation. “One of our most common problems is when the user grabs the device in their hand to talk, which affects the harmonics of the unit,” he says. Another problem is hanging the device too close or too far from the user’s chin.

Still other issues are how to manage and store spare batteries for the mobile phones, and how to handle broken or lost phones (as well as enabling the user to quickly get a replacement).

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Copyright © 2007 IDG Communications, Inc.