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Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
7
Site Survey
Before deploying the Cisco Wireless IP Phone 8821 and 8821-EX into a production environment, a site survey must be
completed by a Cisco certified partner with the advanced wireless LAN specialization. During the site survey the RF spectrum
can be analyzed to determine which channels are usable in the desired band (5 GHz or 2.4 GHz). Typically there is less
interference in the 5 GHz band as well as more non-overlapping channels, so 5 GHz is the preferred band for operation and
even more highly recommended when the Cisco Wireless IP Phone 8821 and 8821-EX is to be used in a mission critical
environment. The site survey will include heatmaps showing the intended coverage plan for the location. The site survey will
also determine which access point platform type, antenna type, access point configuration (channel and transmit power) to use
at the location. It is recommended to select an access point with integrated antennas for non-rugged environments (e.g. office,
healthcare, education, hospitality) and an access point platform requiring external antennas for rugged environments (e.g.
manufacturing, warehouse, retail).
The wireless LAN must be validated to ensure it meets the requirements to deploy the Cisco Wireless IP Phone 8821 and 8821-
EX.
Signal
The cell edge should be designed to -67 dBm where there is a 20-30% overlap of adjacent access points at that signal
level.
This ensures that the Cisco Wireless IP Phone 8821 and 8821-EX always have adequate signal and can hold a signal
long enough in order to roam seamlessly where signal based triggers are utilized vs. packet loss triggers.
Also need to ensure that the upstream signal from the Cisco Wireless IP Phone 8821 and 8821-EX meets the access
point’s receiver sensitivity for the transmitted data rate. Rule of thumb is to ensure that the received signal at the access
point is -67 dBm or higher.
It is recommended to design the cell size to ensure that the Cisco Wireless IP Phone 8821 and 8821-EX can hold a
signal for at least 5 seconds.
Channel Utilization
Channel Utilization levels should be kept under 40%.
The Cisco Wireless IP Phone 8821 and 8821-EX convert the 0-255 scale value to a percentage, so 105 would equate to
around 40% in the Cisco Wireless IP Phone 8821 and 8821-EX.
Noise
Noise levels should not exceed -92 dBm, which allows for a Signal to Noise Ratio (SNR) of 25 dB where a -67 dBm
signal should be maintained.
Also need to ensure that the upstream signal from the Cisco Wireless IP Phone 8821 and 8821-EX meets the access
point’s signal to noise ratio for the transmitted data rate.
Packet Loss / Delay
Per voice guidelines, packet loss should not exceed 1% packet loss; otherwise voice quality can be degraded
significantly.
Jitter should be kept at a minimal (< 100 ms).
Retries
802.11 retransmissions should be less than 20%.
Multipath
Multipath should be kept to a minimal as this can create nulls and reduce signal levels.