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Mesh Network Components
Criteria to Choose the Best Parent
AWPP follows this process in selecting parents for a RAP or MAP with a radio backhaul:
• A list of channels with neighbors is generated by passive scanning in the scan state, which is a subset
of all backhaul channels.
• The channels with neighbors are sought by actively scanning in the seek state and the backhaul channel
is changed to the channel with the best neighbor.
• The parent is set to the best neighbor and the parent-child handshake is completed in the seek state.
• Parent maintenance and optimization occurs in the maintain state.
This algorithm is run at startup and whenever a parent is lost and no other potential parent exists, and is usually
followed by CAPWAP network and controller discovery. All neighbor protocol frames carry the channel
information.
Parent maintenance occurs by the child node sending a directed NEIGHBOR_REQUEST to the parent and
the parent responding with a NEIGHBOR_RESPONSE.
Parent optimization and refresh occurs by the child node sending a NEIGHBOR_REQUEST broadcast on
the same channel on which its parent resides, and by evaluating all responses from neighboring nodes on the
channel.
A parent mesh access point provides the best path back to a RAP. AWPP uses ease to determine the best path.
Ease can be considered the opposite of cost, and the preferred path is the path with the higher ease.
Ease Calculation
Ease is calculated using the SNR and hop value of each neighbor, and applying a multiplier based on various
SNR thresholds. The purpose of this multiplier is to apply a spreading function to the SNRs that reflects
various link qualities.
Figure 21: Parent Path Selection, on page 45
through MAP1 because the adjusted ease value (436906) though this path is greater then the ease value
(262144) of the direct path from MAP2 to RAP.
Figure 21: Parent Path Selection
Parent Decision
A parent mesh access point is chosen by using the adjusted ease, which is the ease of each neighbor divided
by the number of hops to the RAP:
adjusted ease = min (ease at each hop) Hop count
OL-27593-01
shows the parent path selection where MAP2 prefers the path
Cisco Mesh Access Points, Design and Deployment Guide, Release 7.3
Adaptive Wireless Path Protocol
45
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