Руководство По Проектированию для Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter
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Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 9 VoWLAN Design Recommendations
Cell Edge Design
The amount of buffer memory, CPU speed, and radio quality are key factors of the performance of an
AP radio. QoS features prioritize the voice and data traffic in the channel. For a further discussion of
QoS, see
AP radio. QoS features prioritize the voice and data traffic in the channel. For a further discussion of
QoS, see
The 802.11e, WMM, and Cisco Compatible Extension specifications help balance and prevent the
overloading of a cell with voice streams. CAC determines whether there is enough channel capacity to
start a call; if not, the phone may scan for another channel. The primary benefit of U-ASPD is the
preservation of WLAN client power by allowing the transmission of frames from the WLAN client to
trigger the forwarding of client data frames that are being buffered at the AP for power saving purposes.
The Neighbor List option provides the phone with a list that includes channel numbers and channel
capacity of neighboring APs. This is done to improve call quality, provide faster roams, and improve
battery life.
overloading of a cell with voice streams. CAC determines whether there is enough channel capacity to
start a call; if not, the phone may scan for another channel. The primary benefit of U-ASPD is the
preservation of WLAN client power by allowing the transmission of frames from the WLAN client to
trigger the forwarding of client data frames that are being buffered at the AP for power saving purposes.
The Neighbor List option provides the phone with a list that includes channel numbers and channel
capacity of neighboring APs. This is done to improve call quality, provide faster roams, and improve
battery life.
For a further discussion of U-APSD and CAC, see
Cell Edge Design
Guidelines for deploying 802.11b/g/a VoWLAN handsets recommend a design where a minimum power
of -67 dBm is present at the cell boundary (see
of -67 dBm is present at the cell boundary (see
). This practice creates cell sizes that are
smaller than those used in data WLAN designs of the past. The -67 dBm threshold is a general
recommendation for achieving a packet error of one percent, which requires an SNR value of 25 dB or
greater (local noise conditions impact this requirement). Therefore, when determining the likely channel
coverage area for a particular phone type, both signal strength and noise, measured at the phone, must
be verified using the client statistics offered through the AP. See
recommendation for achieving a packet error of one percent, which requires an SNR value of 25 dB or
greater (local noise conditions impact this requirement). Therefore, when determining the likely channel
coverage area for a particular phone type, both signal strength and noise, measured at the phone, must
be verified using the client statistics offered through the AP. See
and
for
determining these values on the standalone and LWAPP APs.
The -67 dBm signal strength measurement has been used by 802.11b phone vendors for a number of
years, and tests indicate that this same rule of thumb measurement also works well for 802.11g and
802.11a phone clients.
years, and tests indicate that this same rule of thumb measurement also works well for 802.11g and
802.11a phone clients.
Figure 9-12
Cell Edge Measurements
Chanel 1
The RADIUS
of the Cell
Should be:
–67 dBm
The Separation of
Same Channel Cells
Should be:
19 dBm
Same Channel Cells
Should be:
19 dBm
–67 dBm
–86 dBm
Chanel 11
Chanel 6
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