Individual GMK per meter is not possible.
But every G3-PLC device can support up to two GMK (with index 0 and 1) at the same time.
During re-keying procedure DC may rekey meters one by one, e.g. providing new GMK key index 1 while index 0 is used for network communication.
When all meters in the network received new GMK, DC will send an activation command to meters to activate it. Upon receiving activation command meters
start using new GMK (e.g. index 1). Since some meters may miss activation command, there is a transition period when both old and new GMK can be used and it
does not interrupt network communication.
Usually, a meter application should support some timeout mechanism. If there is no communication with DC for quite long time (e.g. several hours or day), the meter will try to rejoin the network.
In this case, DC can stop communicating with meters in the network for time which exceeds INACTIVITY_TIMEOUT and force meters to rejoin the network.
When meters rejoin the network, they will get a new GMK key.
This method of rekeying is simple but introduces a significant delay.