provider edge router in context of an lsp is a terminating
or originating end of a given lsp.
in case of origination, a non-mpls packet arrives on an interface, pe router imposes
label(s) before the payload header (ethernet or ip) and forwards
the packet toward it's destination.
in case of termination, it removes the outermost label and it's value indicates the
vpn where the packet have to be forwarder without mpls header.