This illustration uses the image established in figure 1.1, and used again in figure 2.1, of the interconnected system of networks, including a Mobile Network, a National or Global ISP, a Local or Regional ISP, a Home Network, and an Enterprise Network. However, this image incorporates a series of protocol stacks. There are six in total; four of them appear as:

Two of these protocol stacks are associated with routers in the Local or Regional ISP; one is associated with a router in the Home Network; and one is associated with a router in the Enterprise Network.

Two other protocol stacks appear as:

One of these protocol stacks is associated with a laptop computer in the Home Network, which here represents one of the hosts of an application process. The other protocol stack is associated with a server in the Enterprise Network, which here represents the other host of an application process. These two protocol stacks are connected by a blue arrow that points back and forth between them, which is labeled "Logical end-to-end-transport."