Cisco Cisco Aironet 1522 Lightweight Outdoor Mesh Access Point 디자인 가이드
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Cisco Mesh Access Points, Design and Deployment Guide, 7.2
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Design Considerations
Design Considerations
Each outdoor wireless mesh deployment is unique, and each environment has its own challenges with
available locations, obstructions, and available network infrastructure. Design requirements driven by
expected users, traffic, and availability needs are also major design criteria. This section describes
important design considerations and provides an example of a wireless mesh design.
available locations, obstructions, and available network infrastructure. Design requirements driven by
expected users, traffic, and availability needs are also major design criteria. This section describes
important design considerations and provides an example of a wireless mesh design.
Wireless Mesh Constraints
The following are a few system characteristics to consider when you design and build a wireless mesh
network. Some of these characteristics apply to the backhaul network design and others to the CAPWAP
controller design.
network. Some of these characteristics apply to the backhaul network design and others to the CAPWAP
controller design.
Wireless Backhaul Data Rate
Backhaul is used to create only the wireless connection between the access points. The backhaul
interface by default is 802.11a or 802.11a/n depending upon the access point. The rate selection is
important for effective use of the available RF spectrum. The rate can also affect the throughput of client
devices, and throughput is an important metric used by industry publications to evaluate vendor devices.
interface by default is 802.11a or 802.11a/n depending upon the access point. The rate selection is
important for effective use of the available RF spectrum. The rate can also affect the throughput of client
devices, and throughput is an important metric used by industry publications to evaluate vendor devices.
Dynamic Rate Adaptation (DRA) introduces a process to estimate optimal transmission rate for packet
transmissions. It is important to select rates correctly. If the rate is too high, packet transmissions fail
resulting in communication failure. If the rate is too low, the available channel bandwidth is not used,
resulting in inferior products, and the potential for catastrophic network congestion and collapse.
transmissions. It is important to select rates correctly. If the rate is too high, packet transmissions fail
resulting in communication failure. If the rate is too low, the available channel bandwidth is not used,
resulting in inferior products, and the potential for catastrophic network congestion and collapse.
Data rates also affect the RF coverage and network performance. Lower data rates, for example 6 Mbps,
can extend farther from the access point than can higher data rates, for example 300 Mbps. As a result,
the data rate affects cell coverage and consequently the number of access points required. Different data
rates are achieved by sending a more redundant signal on the wireless link, allowing data to be easily
recovered from noise. The number of symbols sent out for a packet at the 1-Mbps data rate is higher than
the number of symbols used for the same packet at 11 Mbps. Therefore, sending data at the lower bit
rates takes more time than sending the equivalent data at a higher bit rate, resulting in reduced
throughput.
can extend farther from the access point than can higher data rates, for example 300 Mbps. As a result,
the data rate affects cell coverage and consequently the number of access points required. Different data
rates are achieved by sending a more redundant signal on the wireless link, allowing data to be easily
recovered from noise. The number of symbols sent out for a packet at the 1-Mbps data rate is higher than
the number of symbols used for the same packet at 11 Mbps. Therefore, sending data at the lower bit
rates takes more time than sending the equivalent data at a higher bit rate, resulting in reduced
throughput.
A lower bit rate might allow a greater distance between MAPs, but there are likely to be gaps in the
WLAN client coverage, and the capacity of the backhaul network is reduced. An increased bit rate for
the backhaul network either requires more MAPs or results in a reduced SNR between MAPs, limiting
mesh reliability and interconnection. For more information about configuring wireless backhaul data
rate, see the
WLAN client coverage, and the capacity of the backhaul network is reduced. An increased bit rate for
the backhaul network either requires more MAPs or results in a reduced SNR between MAPs, limiting
mesh reliability and interconnection. For more information about configuring wireless backhaul data
rate, see the
Note
The data rate can be set on the backhaul on a per AP basis. It is not a global command.
The required minimum LinkSNR for backhaul links per data rate is shown in
.
Table 13
Backhaul Data Rates and Minimum LinkSNR Requirements
802.11a Data Rate (Mbps)
Minimum Required LinkSNR (dB)
54
31
48
29
36
26