This illustration is similar to the one in figure 9.11, however here H1, H2, H3, and H4 are all depicted as telephones. H1 and H2 still share a link-layer switch between them, as do H3 and H4, and the two link-layer switches connect to each other, with routers R1 and R2 between them connected by a 1.5 Mbps link.

H1 sends a dark blue data packet, labeled "1 Mbps audio," through the switch to R1. H2 sends a light blue data packet, also labeled "1 Mbps audio," through the switch to R1. In R1, we see three dark blue packets bearing black stripes and three light blue packets bearing gray stripes.