MSM7xx Controllers Configuration Guide v6.4.0

DefinitionTerm
The wireless connection between two nodes.Link
A link that transports data away from the root network.Downstream link
A link that transports data towards the root network.Upstream link
Any two connected nodes are peers. In the diagram, AP 1 is the peer of both AP 2
and AP 3.
Peer
Local mesh operational modes
Three different roles can be assigned to a local mesh node: Master, Alternate Master, or Slave.
Each role governs how upstream and downstream links are established by the node.
• Master: Root node that provides the upstream link to the ground network that the other nodes
want to reach. The master never tries to connect to any other node. It waits for links from
downstream alternate master or slave nodes.
NOTE: It is possible to have several masters for the same mesh ID connected to the ground
network. This can be used to provide redundant paths to the ground network for downstream
nodes.
• Alternate Master: First establishes an upstream link with a master or alternate master node.
Next, operates as a master node waiting for links from downstream alternate master or slave
nodes.
• Slave: Can only establish an upstream link with master or alternate master node. Slave nodes
cannot establish downstream links with other nodes.
Node discovery
Discovery of another node to link with is limited to nodes with the same mesh ID. The link is
established with the node that has the best score based on the following calculation:
Score = SNR - (Number of hops x SNR cost of each hop)
If a node looses its upstream link, it automatically discovers and connects to another available
node.
NOTE: A master or alternate master must be seen with an SNR of 20 or higher before a slave
will attempt to connect to it.
Operating channel
If a mesh operates on a dynamic frequency selection (DFS) channel, the master node selects the
operating channel. If another node detects radar and switches channels, that node reports the
channel switch to the master node, which initiates a channel switch for the nodes connected to it.
This allows the local mesh to converge on a specific channel.
A node that uses a DFS channel and that loses connection with its master, scans channels to find
a master on another channel, which can be a new master or the same master.
If the local mesh does not operate on a DFS channel, configure the radios in one of the following
ways:
• Configure the radios on all nodes to use the same fixed channel.
• Configure the radios for automatic channel selection. In this case the master selects the least
noisy channel. Slaves and alternate masters scan channels until they find the master, then tune
to the master channel and link with the master.
386 Local mesh