A customer with a small enterprise network of 15 remote sites is trying to optimize its VPN by migrating some remote sites using Frame Relay connections to the Internet to using cable connections to the Internet. Minimizing costs is one of the customer's highest priorities. Only a moderate amount of IP traffic is passing through the network, most of which is from the remote sites to the central site. IPSec should be used to provide VPN functionality and basic confidentiality is desired. Based on the traffic patterns, which topology would be the easiest for this customer to set up and manage?