BigFix Client Last Reporting Issue

Hello All,
I have read in BigFix arch document states that BigFix client last report time is getting updated from ICMP protocol. But want to understand better, whether these last report date and time will be posted to fillDB buffer directory folder before writing to DB or how it works?

Please help me to understand.

ICMP is used by the client to find its closest relay.

Last Report Time is when the client last posted a report. These reports are passed up the relay chain to the root server, where they are collected by FillDB and the contents are parsed and posted to the DB,