User's Manual

Page 30 E2 Wireless I/O
3.4 WIBMesh
The ELPRO WIBMesh protocol is based on the “Ad hoc On-demand Distance Vector”
(AODV) routing algorithm which is a routing protocol designed for ad hoc networks.
AODV is capable of unicast (single addressed message) and multicast (Broadcast to
all) routing and is an “on-demand” protocol, meaning that it builds and maintains these
routes only as long as they are needed by the source devices. Another words the
network is silent until a connection is needed. The Protocol creates a table, which
shows the connection routes to other device in the system and uses sequence numbers
to ensure the routes are kept as current as possible.
When a module in a network needs to make a connection to another module it
broadcasts a request for connection. Other modules forward this message, and record
the module address that they heard it from, creating a table of temporary routes back to
the starting module. If a module receives a message and it already has an existing
route to it, it will send a message backwards through the temporary route to the
requesting module.
Each request for a route has a sequence number. Modules use this sequence number
so that they do not repeat route requests that they have already passed on. Another
such feature is that the route requests have a "time to live" number that limits how many
times they can be retransmitted. Another such feature is that if a route request fails,
another route request may not be sent until twice as much time has passed as the
timeout of the previous route request.
The original starting module then begins using the route that has the least number of
hops. Unused entries in the routing tables are recycled after a time.
When a link fails, a routing error is passed back to a transmitting node, and the process
repeats.