This eighth installment in our WirelessHART protocol technical discussion examines the difference between two routing protocols: graph routing and Ad hoc On-Demand Distance Vector (AODV) routing. AODV is utilized for mobile ad hoc networks (MANETs like Zigbee) and other wireless ad hoc networks.
What is AODV?
AODV is something like the game Six Degrees of Kevin Bacon. You know how this works. Someone names an actor and everyone tries to find the shortest path of association to Kevin Bacon.
For example, Bela Lugosi was in Abbott and Costello Meet Frankenstein (1948) with Vincent Price, who was in The Raven (1963) with Jack Nicholson, was in A Few Good Men (1992) with Kevin Bacon. Therefore, Beli Lugosi is three degrees removed from Kevin Bacon, or has a so-called “Bacon number” of 3.
In AODV, when a network node needs a connection it broadcasts a request for connection. Other AODV nodes receiving the broadcast record the node they received it from and forward message. When a node already having a route to the desired destination receives the message it sends a message backwards through a temporary route to the requesting node. The original source node chooses the route with the least number of hop. It’s like looking for the lowest Bacon number.
Which is better?
AODV is an on-demand routing protocol. In other words, routes are only created when they are needed by a network device. The main advantage is network devices do not need much memory or processing power to implement the protocol.
One disadvantage is a device may have a route sored which is no longer valid. When it passes this back to the source device, a route may be chosen which no longer works. A second disadvantage is the flood of network traffic when a route is being established. This protocol may be useful for short, intermittent transmissions on a small network with few nodes, but it could experience dangerous latency issues on a larger network.
WirelessHART utilizes graph routing. This requires more processing power since each device must be able to reroute the transmission if necessary. Graph routing creates a more reliable transmission path, since it is self-repairing. AODV has its place, but in a large industrial network where timely, reliable transmissions are critical, graph routing has the advantage.