Final answer:
The overlay network is built on top of the underlay network to provide additional services or features that are not available in the underlay network.
Step-by-step explanation:
The subject of this question is related to Computer Networks.
An overlay network is a virtual network that is built on top of an existing underlay network. It provides additional services or features that are not available in the underlay network. On the other hand, the underlay network refers to the physical network infrastructure that provides the basic connectivity between network nodes.
For example, in a virtual private network (VPN), the overlay network is created on top of the underlay network to provide secure communication between remote users. The VPN uses encryption and tunneling protocols to establish a secure connection over the public internet.