STP-RSTP query

Hi

I have a couple of queries on the implementation of STP and RSTP.

1. How different is the behavior of RSTP in a shared LAN? In a scenario where there are multiple RSTP ports on a switch, all of which are on a same shared LAN segment, how will the proposal-agreement mechanism works? Something like ports 1,2,3,4 of switch A and ports

1,2,3,4 of switch B connected to the same LAN segment. In this case, will the sender of the proposal expect an agreement from all the other ports of the other switch?

1. In STP, once the network becomes stable, root bridge will send the BDPUs and the intermediate bridges will relay them on to their designated ports. What all fields in the BPDU are modified by these bridges before forwarding them? (like path cost) Will the source address be changed by these intermediate bridges?

2. Whether the BPDUs are always sent as multicast in both STP(for both TCN and TCA as well) and RSTP?

Thanks in advance.