Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter デザインガイド
3-18
Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 3 WLAN Radio Frequency Design Considerations
Planning for RF Deployment
Figure 3-8
Coverage Comparison and AP Density for Different Data Rates
The data rate you choose depends on the type of application to be supported, but should not be greater
than the typical requirements because there is trade-off in coverage. In a typical WLAN environment,
the higher data rates give maximum throughput and should minimize performance-related support
issues. The physical facility and/or whether the network is client-centric generally dictates range
requirements; some clients might not support the higher data rates, longer ranges, or the delay and jitter
rates of an infrastructure element such as an AP.
than the typical requirements because there is trade-off in coverage. In a typical WLAN environment,
the higher data rates give maximum throughput and should minimize performance-related support
issues. The physical facility and/or whether the network is client-centric generally dictates range
requirements; some clients might not support the higher data rates, longer ranges, or the delay and jitter
rates of an infrastructure element such as an AP.
It might seem logical to choose the default configuration of APs and clients, thereby allowing all data
rates. However, there are three key reasons for limiting the data rate to the highest rate at which full
coverage is obtained:
rates. However, there are three key reasons for limiting the data rate to the highest rate at which full
coverage is obtained:
•
Broadcast and multicast (if enabled) are sent at the lowest associated data rate (to ensure that all
clients can receive the packets). This reduces the throughput of the WLAN because traffic must wait
until frames are processed at the slower rate.
clients can receive the packets). This reduces the throughput of the WLAN because traffic must wait
until frames are processed at the slower rate.
•
Clients that are farther away, and therefore accessing the network at a lower data rate, decrease the
overall throughput by causing delays while the lower bit rates are being serviced. It might be better
to force the clients to roam to a closer AP so as not to impact the performance of the rest of the
network.
overall throughput by causing delays while the lower bit rates are being serviced. It might be better
to force the clients to roam to a closer AP so as not to impact the performance of the rest of the
network.
•
If a 54 Mbps service is specified and provisioned with APs to support all data rates (for example),
clients at lower rates can associate with the APs that can create a coverage area greater than planned,
thereby increasing the security exposure (by allowing association from outside the building) and
potentially interfering with other WLANs.
clients at lower rates can associate with the APs that can create a coverage area greater than planned,
thereby increasing the security exposure (by allowing association from outside the building) and
potentially interfering with other WLANs.
Surveyed at 11 Mbps
Surveyed at 24 Mbps
74191