SpectraLink NetLink Wireless Telephones Best Practices White Paper Wireless Telephone - Manual (Page 3)

White Paper
Page 2
2.1 Coverage
One of the most critical issues in deploying NetLink Wireless
Telephones is ensuring sufficient wireless coverage. Often enterprise
Wi-Fi networks are designed only for data applications and may not
provide adequate coverage for wireless telephone users. Quite often
these networks are designed to cover only areas where data terminals
will be used, and do not include coverage in other areas such as
stairwells, bathrooms, building entrances, or lobby areas where NetLink
handsets may be used.
The overall quality of coverage is also more important with telephony
applications. Coverage that is suitable for data applications may not be
adequate for Wi-Fi telephony. Most data communication protocols
provide a mechanism for retransmission of lost or corrupted packets.
Delays caused by retransmissions are not harmful, or even discernable,
for most data applications. However, the real-time nature of a full-duplex
telephone conversation requires that voice packets need to be received
correctly within tens of milliseconds of their transmission. There is little
time for retransmission; lost or corrupted packets must be discarded. In
areas of poor coverage, data application performance may be
acceptable due to retransmission protocols, but real-time voice quality
may not be acceptable.
Another factor to consider in determining the coverage area is the device
usage. Wireless telephone devices are used differently than wireless
data terminals. Telephone users tend to walk as they talk, while data
users are most often stationary. NetLink Wireless Telephones are
usually held next to the user’s head, introducing additional radio signal
attenuation. Data terminals are usually set on a surface or held out at
arms length so the user’s body has little affect. Because of these
factors, a wireless telephone may have less range than a data terminal
and the wireless LAN layout should account for a general reduction in
radio signal propagation.
2.1.1 Overlapping
Coverage
To provide comprehensive coverage for Wi-Fi telephony applications,
APs need to be positioned with sufficient overlapping coverage to
ensure that there are no coverage gaps, or dead spots, between them.
As NetLink Wireless Telephones move out of range of a particular AP,
they seek out another AP to hand-off to, or re-associate with, in order to
maintain their network connection. A properly designed Wi-Fi network
will provide seamless hand-offs between APs, ensuring excellent voice
quality throughout the facility.
The wireless LAN layout must factor in the transmission settings that will
be configured within the APs. The transmission of voice requires
relatively low data rates and a small amount of bandwidth compared to
other applications. The 802.11 standard includes data rate reduction
specifications so that as a user moves away from the access point, the
radio adapts and uses a less complex and slower mechanism to send
the data. The result is increased range (coverage) when operating at
reduced transmission rates. Access points should generally not be
configured to limit the transmission to only the higher rates if wireless