Your messaging network topology is determined by the way your organization has identified its sites.
Typical network topologies include sites with:
Distributed application roles
Centralized application roles
Small organizations typically require an easy-to-deploy single-server topology that is ready to grow with the needs of the organization. Large organizations can use the examples discussed in Planning for Messaging as building blocks for their enterprise-wide network architecture, including:
Conforming to an existing network topology
Fitting into centralized data centers
Supporting local survivability networks
Meeting high availability requirements
Supporting disaster recovery requirements
Note An application server can support only one site.