the contents of a web page are encapsulated with an HTTP header, then by a TCP header, an IP header, and, finally, by a frame header and trailer. The frame is forwarded to the destination node as a stream of bits, where it is decapsulated into the respective PDUs and interpreted at each layer by the receiving node.

The result of encapsulation is that each lower-layer provides a service to the layer or layers above it, while at the same