User Manual

SPEEDLAN 9000 Series Installation and Operation User Guide Version 3.03
Introduction 1-11
Topology Updates
When a router adds or deletes a neighbor to or from its active neighbor list, it
propagates that information to the rest of the routers in the wireless mesh LAN. Unlike
classic wired routing protocols, topology update notifications are not flooded. Instead
they are sent via a spanning tree, such that each router receives only one notification of
a particular event. (A brief explanation of the spanning tree algorithm is explained in
the note below.) This approach also conserves bandwidth for use in forwarding user
traffic. Since each router knows the topology of the entire wireless LAN, it can
determine the shortest path to each peer router in the wireless LAN.
Note: In short, the spanning tree algorithm enables units to dynamically locate a
subset of the topology that is loop-free. The spanning tree algorithm determines the
best path a unit can use to send a message.
Routing
Routing is simply the act of forwarding a received Internet Protocol (IP) datagram (a
block of data) toward its destination. The router compares the destination IP address to
entries in its routing table. If the destination is a wireless neighbor or a node connected
to the router's wired LAN, the router sends the datagram directly to the destination.
Otherwise, it sends the datagram to another router, which must be on the wired LAN or
be a wireless neighbor.
In wired broadcast LANs, all routers on the LAN can hear each other. Therefore, a
datagram only passes through a router when it is moving from one LAN to another LAN
along the path to its destination. In a mesh wireless LAN, not all routers can hear each
other. Therefore, a router within a wireless LAN may forward a datagram to a neighbor
router within the same wireless LAN, in order to send the datagram toward its
destination. For each datagram, the routing algorithm minimizes the number of router-
to-router hops within the wireless LAN, thereby also conserving bandwidth for other
user traffic.