Consensus is achieved when a required number of observations are made for a
particular data point. The CCIP plugins are built using the OffChain Reporting
(OCR) framework to manage collecting observations from a permissioned set of
nodes. The required threshold of observations is derived from the value F,
for strict observations we would require 2 * F + 1 observations. In other
cases F + 1 observations are allowed. The number of nodes participating is
derived from 3 * F + 1.
The CCIP plugins introduce the "Role DON" protocol built as a gossip layer ontop of OCR, this allows for multiple distinct groups of observations. For CCIP the roles assigned to a node indicate which chains they should be observing. It is no longer a requirement for all nodes to support all chains.
Each role has its own F value. In order to distinguish between them there are
two new terms:
- FRoleDON: the OCR level F which determines observation thresholds for
the OCR instance, previously
F. - FChain: the role level F which determines the observation threshold for each role.
Because OCR is a permissioned network, roles are assigned during configuration. The plugins must ensure observations for each chain are only made by the designated nodes.
Each role also has its own value for FChain. This value determines the number
of nodes we should configure as 3 * FChain + 1 along with the strict
strict observation threshold as 2 * FChain + 1.