Cisco aironet 1522 Design And Deployment Manual page 36

Design Considerations
–
Table 9
Data Rate
54 Mb/s
48 Mb/s
36 Mb/s
24 Mb/s
18 Mb/s
12 Mb/s
9 Mb/s
6 Mb/s
The required minimum LinkSNR value is driven by the data rate and the following formula:
•
Minimum SNR + fade margin.
–
–
–
Table 10
Date Rate
6
9
12
18
24
36
Number of backhaul hops is limited to eight, but three to four is recommended
•
The number of hops is recommended to be limited to three or four primarily to maintain sufficient
backhaul throughput, because each mesh access point uses the same radio for transmission and
reception of backhaul traffic. This means that throughput is approximately halved over every hop.
For example, the maximum throughput for 24 Mb/s is approximately 14 Mb/s for the first hop,
9 Mb/s for the second hop, and 4 Mb/s for the third hop.
• Number of MAPs per RAP
Cisco Aironet 1520, 1130, 1240 Series Wireless Mesh Access Points, Design and Deployment Guide, Release 6.0
36
To set the mesh backhaul bit rate for each access point, choose Wirless > Access Points
Note
> All APs, then click an AP name and click the Mesh tab.
The required minimum LinkSNR for backhaul links per data rate is shown in
Backhaul Data Rates and Minimum LinkSNR Requirements
Minimum SNR refers to an ideal state of non-interference, non-noise, and a system packet error
rate (PER) of no more than 10%
Typical fade margin is approximately 9 to 10 dB
We do not recommend using data rates greater than 24 Mb/s in municipal mesh deployments as
the SNR requirements do not make the distances practical
Minimum Required LinkSNR Calculations by Data Rate
Minimum SNR (dB) +
5
6
7
9
13
17
Minimum Required LinkSNR (dB)
31
29
26
22
18
16
15
14
Table 10 summarizes the calculation by data rate.
Fade Margin =
9
9
9
9
9
9
Table 9.
Minimum Required
LinkSNR (dB)
14
15
16
18
22
26
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