RRC连接重配疑问

why0727

在RRC连接重配时，协议中提到：
re-establish PDCP for SRB2 and for all DRBs that are established, if any;
re-establish RLC for SRB2 and for all DRBs that are established, if any;


resume SRB2 and all DRBs that are suspended, if any;




这里的重建PDCP/RLC，以及resume SRB2/all DRBs，到底是什么意思？