VPRN Data Plane is the place that the traffic is sent and received generally. As we mentioned before, CE devices are the devices that are not MPLS capable.They do not know labels. So, they send the data to the PE device as unlabeled.
PE router get this packet and add a pre-determined VPN (Inner) Label to each packet. This PE router has learned this VPN Label via MP-BGP before. PE router also add a Transport (Outher) Label to the packet. This is learned via LDP. This processes are “Push Process” of MPLS Labelling.
Here, there is a Label Stack and this label stack consist of Transport (Outher) and VPN (Inner) Labels. This is the beginning point of the Layer 3 VPN Service path, LSP.