What is the specific functionality of a PF(Physical Function) in SR-IOV ? Also what is the difference between virtual function and a physical function ? Does the VF communicate with a PF during the transfer of a packet from the VM ?

What is the specific functionality of a PF(Physical Function)  in SR-IOV ? Also what is the difference between virtual function and a physical function ? Does the VF communicate with a PF during the transfer of a packet from the VM ?@