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Site Survey Guide for Deploying Cisco 7920 IP Phones
OL-6315-01
Chapter 1 Overview
Recommendations for Successful VoIP Surveys
Figure 1-2 Signal to Noise Ratio
Minimum Requirements for WIPT Cells
Table 1-1 lists the minimum values for voice and data cells. For WIPT cells, Cisco recommends that the
cell edge be –67 dBm and the SNR be 25 dB using a data rate of 11 Mbps. These values are much more
restrictive than those needed for data because of the sensitivity to delays and retries for voice clients.
Figure 1-3 shows how the difference in transmit powers between the access point and the WIPT client
creates different effective ranges. The 5 mW signal probably would continue all the way to the access
point, but if the access point antennas do not have enough gain to make up the difference in received
signal of the WIPT client, then the WIPT packets will not be decoded. A high-gain antenna on an access
point will receive a signal from a 5-mW client from a greater distance than a low-gain antenna. It is the
Table 1-1 Minimum Signal Strength and Signal to Noise Ratios for Voice and Data Cells
Data Rate (Mbps)
Data Cell WIPT Cell
Minimum Cell
Edge Signal
Strength Minimum SNR
Minimum Cell
Edge Signal
Strength Minimum SNR
54 –71 25 — —
36 –73 18 — —
24 –77 12 — —
12 or 11 –82 10 –67 25
6 or 5.5 –89 8 –74 23
2 –91 6 –76 21
1 –94 4 –79 19
