8.3. DIO Transmission
RPL nodes transmit DIOs using a Trickle timer [RFC6206]. A DIO from a sender with a lesser DAGRank that causes no changes to the recipient's parent set, preferred parent, or Rank SHOULD be considered consistent with respect to the Trickle timer.
The following packets and events MUST be considered inconsistencies with respect to the Trickle timer, and cause the Trickle timer to reset:
o When a node detects an inconsistency when forwarding a packet, as detailed in Section 11.2.
o When a node receives a multicast DIS message without a Solicited Information option, unless a DIS flag restricts this behavior.
o When a node receives a multicast DIS with a Solicited Information option and the node matches all of the predicates in the Solicited Information option, unless a DIS flag restricts this behavior.
o When a node joins a new DODAG Version (e.g., by updating its DODAGVersionNumber, joining a new RPL Instance, etc.).
Note that this list is not exhaustive, and an implementation MAY consider other messages or events to be inconsistencies.
A node SHOULD NOT reset its DIO Trickle timer in response to unicast DIS messages. When a node receives a unicast DIS without a Solicited Information option, it MUST unicast a DIO to the sender in response. This DIO MUST include a DODAG Configuration option. When a node receives a unicast DIS message with a Solicited Information option and matches the predicates of that Solicited Information option, it MUST unicast a DIO to the sender in response. This unicast DIO MUST include a DODAG Configuration option. Thus, a node MAY transmit a unicast DIS message to a potential DODAG parent in order to probe for DODAG Configuration and other parameters.
8.3.1. Trickle Parameters
The configuration parameters of the Trickle timer are specified as follows:
Imin: learned from the DIO message as (2^DIOIntervalMin) ms. The default value of DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN.
Imax: learned from the DIO message as DIOIntervalDoublings. The default value of DIOIntervalDoublings is DEFAULT_DIO_INTERVAL_DOUBLINGS.
k: learned from the DIO message as DIORedundancyConstant. The default value of DIORedundancyConstant is DEFAULT_DIO_REDUNDANCY_CONSTANT. In RPL, when k has the value of 0x00, this is to be treated as a redundancy constant of infinity in RPL, i.e., Trickle never suppresses messages.