Cisco Systems 7920 manual ADU CB21

Chapter 2 Survey Tools

Figure 2-2 AirMagnet Packet Decode Tool

The 7920 survey tool reports the signal strength of the signal from the access point as an RSSI value. Most client card utilities report signal strength as dBm or percent of signal strength. In this chapter, each of the tools tested will be reviewed showing how they measure signal strength. Table 2-1provides a cross reference of RSSI, dBm, and percent of signal strength as reported by different cards and utilities. The numbers were captured in a live over-the-air test with each device in the same location for comparison. These are not exact numbers. A plus or minus of five percent in radio-to-radio performance is considered within tolerance. All surveys regardless of the tool used must be measured to the signal strength requirements of the 7920. Cisco recommends that cell size for the 7920 be an RSSI value of 35 for the 7920 survey utility; this equals a PCM350 ACU value of -67 dBm and a Cisco a/b/g client Aironet Desktop Utility (ADU) value of -66dBm.

Table 2-1 RSSI, dBm, and Signal Strength Cross-Referenced for 7920 Phones

1200 Series Access Point @ 11 Mbps @ 20 mW with 2.2 dBm Antennas

				SniffPro	access		350 ACU	AirMagnet	AiroPeek	ADU CB21
			Feet	Signal %	point dBm	7920 RSSI	dBm	350 (PDA)	CB21 dBm	dBm
10				78	–55	52	> –45	–47	–51	–51
20				72	–60	46	–52	–49	–52	–53
30				68	–67	46	–55	–54	–58	–60
40				63	–72	43	–59	–54	–68	–68
50				68	–74	37	–59	–58	–68	–70
60				72	–72	38	–63	–64	–68	–67
70				30	–78	35	–67	–67	–68	–66
		Site Survey Guide for Deploying Cisco 7920 IP Phones
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