Network interface layer adds IP datagram as data area in hardware frame. Hardware ignores IP datagram message format. Standards for encapsulation defines details.Standard describe data type for IP datagram, as well as others. Receiving protocol stack compiles data area based on frame type. The encapsulation procedure is given in the diagram below.
ENCAPSULATION ACROSS MULTIPLE HOPS:
Each router in the path from the source to the receiver unencapsulates incoming datagram from frame message, processes datagram and calculates next hop and encapsulates datagram in outgoing message frame. Datagram can be encapsulated in different hardware format at every hop. Datagram itself is unmodified as given in the figure below.