Fig: Switching taxonomy (left) and a dedicated reserved circuit versus a store-and-forward packet/message path (right)Fig: X.25 three-layer architecture (physical, LAPB link, PLP packet) versus the leaner Frame Relay stack (physical + data-link core only)Fig: The seven-layer OSI model beside the four-layer TCP/IP model, showing the layer mappingFig: Encapsulation: application data gains a TCP header (segment), an IP header (packet), a data-link header and trailer (frame), then is sent as bits