3.6.5 Message Processing Events and Sequencing Rules
When a message arrives, the responder MUST first check whether it is a valid Charge, Emit, Query, or QueryLargeTlv frame or not. If not, it MUST be dropped.
The responder MUST check if the frame was sent from the currently associated mapper by matching the Real Source Address of the Base Header with the Current Mapper. If the addresses do not match, the responder MUST drop the message. Otherwise, the frame is processed as described in the following sections.