3.5.6.3 Hello Timer Expiry
After this timer fires, a Hello frame MUST be sent, the Txc counter MUST be decremented for each pending session in the Session Table, and each session in the temporary state MUST be deleted. When this counter reaches zero, the session MUST be marked complete even if it has not been acknowledged.
The generation number used in the Hello frame must be the current generation number stored by responder. If a stored generation number is not defined, the generation number SHOULD be set to zero.