Communication at the data-link layer is node-tonode.
A data unit from one point in the Internet
needs to pass through many networks (LANs and
WANs) to reach another point. Theses LANs and
WANs are connected by routers. It is customary to
refer to the two end hosts and the routers as nodes
and the networks in between as links. Figure 9.2 is a
simple representation of links and nodes when the
path of the data unit is only six nodes.