SPECIAL FOCUS: WIRELESS
Is your WLAN ready for voice?
by Chris Kozup
As the business case for voice-over-wireless
LANs has matured, enterprises are beginning
to realize the benefits of adding voice to
their existing wireless LANs. To reap those
benefits, enterprises first need to ensure
the wireless LAN is ready to handle a mix of
data and voice applications.
To ensure that voice over IP delivers the same, if not superior, levels of
quality, IT managers first had to prepare the data network by improving
availability and scalability, while reducing latency and jitter. The wireless
network should be prepared in the same way to accommodate voice traffic.
IT managers should consider three key
phases comprised of design, deployment and
enablement of infrastructure services.
Thoughtful planning around each of these
areas will ensure the wireless LAN is not
only robust, but can also support
mission-critical voice services.
Understanding who will be the primary
user, what services are required and where
those services are needed is the first step
in mapping the technology solution to the
business needs. Start with the
identification of all key stakeholders.
Those stakeholders should then identify the
functional requirements, including elements
such as number of users, applications,
coverage areas, security, roaming
requirements and the integration of other
mobility services, including location
awareness.
Once the functional requirements have
been defined, the key stakeholders can work
to prioritize and align the requirements to
ensure the final service will meet business
needs. Conducting a usability analysis at
this point can be helpful in gaining
broad-based user acceptance.
In the deployment phase, IT should focus
on the technical elements that will optimize
the support for voice. A site survey will
provide an understanding of the existing
radio frequency (RF) characteristics and
align the placement of access points to
mitigate interference and improve coverage.
Automated radio resource-management tools
can increase the visibility into the RF
environment and maintain the integrity of
the RF coverage pattern.
Best-practice implementation guidelines
include: one AP per 2,500-3,000 square feet;
AP transmit power set to 50 mw; AP cell
overlap of 20 percent; AP placement around
the building perimeter; minimum signal
strength of –65 dbm at the coverage edge;
and packet error rates (PER) no higher than
one percent.
In addition, the adoption of wireless
voice requires network intelligence. Wi-Fi
networks present a challenge due to their
variable nature and the fact that unlicensed
frequencies are sometimes subject to
interference. Infrastructure services can
improve the performance of voice traffic as
it crosses the wireless link. Radio
resource-management tools and shifting voice
traffic to underused frequencies (e.g., 5
GHz) can overcome the majority of these
challenges.
Providing tighter quality of service
(QoS) controls can further enhance the voice
quality and prevent chatty or
bandwidth-heavy applications from degrading
the user experience. Infrastructure services
critical to a voice-ready wireless design
include: support for WMM (Wi-Fi Alliance’s
QoS standard); use of WMM power save for
increased device battery life;
wireless-based call-admission control;
planning, deployment, management and
troubleshooting tools; fast secure roaming;
and real-time RF visibility for RF
interference detection and mitigation.
IT organizations should consider the
design and deployment of infrastructure
services when adopting wireless IP
telephony. A little foresight can go a long
way in mobilizing enterprise communications
in a reliable, scalable way.
Chris Kozup is manager, mobility
solutions, for Cisco Systems, San Jose,
Calif.
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