Next, let's define an "encapsulated" mesh.

Above we have the mesh from the previous page, but have drawn an encapsulating circle around it with one node sticking out.

That one node is called the "gateway". It is the only node that is available to the outside world. From the point of view of the outside world, it is the only node that exists.

The nodes inside the circle are hidden. Nothing outside the encapsulating circle can communicate with anything inside it, except by going through the gateway. Nothing outside the encapsulation circle can even know what is inside it.

All internal communications are private; nothing outside it can even know that internal communication is taking place.

The gateway node may examine all communications coming through it. It may accept, reject, or modify communication (data) at will.

Thus, for all practical purposes, the gateway *IS* the node.