What happens during SAP Upgrade Downtime Phase [Execution Phase] ?

Execution (Downtime) Downtime I: 
Set up system for downtime MAIN_PROFSTART MOD_INSTNR_PRE 1/6
Execution (Downtime) Downtime II: 
Conversion, Main Import, XPRAs MAIN_NEWBAS STARTSAP_NBAS 1/2
Execution (Downtime) Downtime end: 
Set up system for uptime MAIN_PROFEND GETSYNC_MODPROF_STARTED 1/1
Execution (Downtime) Transition to uptime