Material Replication from MM to MDM

Hi Seniors,

  I have a doubt about material replication from MM to MDM. I know from MM, the materials will be extracted from MDM_CLNT_EXTR tcode and via PI, it will be sent to MDM system. But, how PI is triggering here? how system is generating idoc to transfer material from MM to MDM? What MDM will do after transferring the data from MM to MDM? Please clear me.

Regards,

Prasad