  Wireless sensor network protocols very often use the Trickle algorithm to
govern information dissemination. For example, the widely used IPv6 Routing
Protocol for Low-Power and Lossy Networks (RPL) uses Trickle to emit control
packets. We derive an analytical model of Trickle to take into account multiple
redundancy constants and the common lack of synchronization among nodes.
Moreover, we demonstrate message count unfairness when Trickle uses a unique
global redundancy constant because nodes with less neighbors transmit more
often. Consequently, we propose a heuristic algorithm that calculates a
redundancy constant for each node as a function of its number of neighbors. Our
calculated redundancy constants reduce unfairness among nodes by distributing
more equally the number of transmitted messages in the network. Our analytical
model is validated by emulations of constrained devices running the Contiki
Operating System and its IPv6 networking stack. Furthermore, results very well
corroborate the heuristic algorithm improvements.
