When you use the centralized topology, you simplify your IT management and lower your total cost of ownership compared to a distributed topology. However, when remote locations connect to Messaging servers over a WAN, your network carries a significant amount of voice traffic. In case of an outage in the network, users at the remote location have no access to the Messaging system until the network is restored. But if you have a high-quality network, your remote locations are not prone to network outages, or your WAN link is inexpensive, the centralized model might be the solution for your organization.