Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter Guia Do Desenho
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Enterprise Mobility 4.1 Design Guide
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Chapter 8 Cisco Wireless Mesh Networking
Design Details
Wireless Mesh Design Constraints
When designing and building a wireless mesh network with the 1500 Mesh AP, there are a number of
system characteristics to consider. Some of these apply to the backhaul network design and others to the
WLC design:
system characteristics to consider. Some of these apply to the backhaul network design and others to the
WLC design:
•
Recommended backhaul is 18 Mbps—18 Mbps is chosen as the optimal backhaul rate because it
aligns with the maximum WLAN coverage distances of the MAP; that is, the distance between
MAPs using 18 Mbps backhaul should allow for seamless WLAN client coverage between the
MAPs. A lower bit rate may allow a greater distance between 1500 Mesh APs, 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 1500 Mesh APs or results in a
reduced SNR between mesh APs, limiting mesh reliability and interconnection. The wireless mesh
backhaul bit rate, like the mesh channel, is set by the RAP.
aligns with the maximum WLAN coverage distances of the MAP; that is, the distance between
MAPs using 18 Mbps backhaul should allow for seamless WLAN client coverage between the
MAPs. A lower bit rate may allow a greater distance between 1500 Mesh APs, 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 1500 Mesh APs or results in a
reduced SNR between mesh APs, limiting mesh reliability and interconnection. The wireless mesh
backhaul bit rate, like the mesh channel, is set by the RAP.
•
Number of backhaul hops should be limited to three to four—The number of hops is recommended
to be limited to three to four primarily to maintain sufficient backhaul throughput, because each
mesh AP 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 an
18 Mbps is approximately 10 Mbps for the first hop, 5 Mbps for the second hop, and 2.5 Mbps for
the third hop.
to be limited to three to four primarily to maintain sufficient backhaul throughput, because each
mesh AP 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 an
18 Mbps is approximately 10 Mbps for the first hop, 5 Mbps for the second hop, and 2.5 Mbps for
the third hop.
•
Number of MAPs per RAP—There is no current software limitation of how many MAPs per RAP
you can configure. However, it is suggested that you limit this to 20 MAPs per RAP to avoid bottle
necks in your mesh.
you can configure. However, it is suggested that you limit this to 20 MAPs per RAP to avoid bottle
necks in your mesh.
•
Number of APs per controller—The number of APs per controller is determined by the controller
capacity.
capacity.
•
Number of controllers—The number of controllers per mobility group is limited to 24.
Client WLAN
The mesh AP client WLAN delivers all the WLAN features of a standard 802.11bg LWAPP deployment
with the full range of security and radio management features.
with the full range of security and radio management features.
The goals of the client WLAN must be considered in the overall mesh deployment:
•
What bit rates are required? Higher bit rates reduce coverage and are limited by the mesh backhaul.
•
What throughput is required? What are the application throughput requirements and how many
simultaneous clients are expected on a Cisco 1500 Mesh AP?
simultaneous clients are expected on a Cisco 1500 Mesh AP?
•
What coverage is required? Is the coverage between different 1500 Mesh APs required to be
contiguous or is the mesh deployment a collection of separate active zones?
contiguous or is the mesh deployment a collection of separate active zones?
•
What security mechanisms are required? Is the WLAN intended for public consumption or private?
What security is needed for client access?
What security is needed for client access?
Bridging Backhaul Packets
Bridging services are treated a little differently from regular controller-based services. There is no outer
DSCP value in bridging packets because they are not LWAPP encapsulated. Therefore, the DSCP value
in the IP header as it was received by the AP is used to index into the table as described in the path from
AP to AP (backhaul).
DSCP value in bridging packets because they are not LWAPP encapsulated. Therefore, the DSCP value
in the IP header as it was received by the AP is used to index into the table as described in the path from
AP to AP (backhaul).