The following figure illustrates the Emergency Responder configuration with two (or more) main sites, each served by a separate PSAP.
Figure 8. Deploying Cisco Emergency Responder in Two Main Sites
You can adapt this example to a more complex setup by combining this discussion with these examples:
If a main site is served by more than one PSAP, see Deployment in Main Site Two or More PSAPs for information about deploying Emergency Responder in that site. To support this type of network:
Install two Emergency Responder servers in Chicago and configure one server as the Publisher and the other server as a Subscriber pointing to the Publisher. After installation, select the Emergency Responder Publisher server in the Chicago Emergency Responder group for use as the cluster database. See Set up Emergency Responder Cluster and Cluster DB Host.
Install two Emergency Responder servers in New York and configure one server as the Publisher and the other server as a Subscriber pointing to the Publisher. After installation, select the Emergency Responder Publisher server in the Chicago Emergency Responder group for use as the cluster database. See Set up Emergency Responder Cluster and Cluster DB Host.
Most likely, there are separate PSAPs serving your main offices. In this example, Chicago and New York use different PSAPs. You need at least one gateway in Chicago, and one in New York, to connect to different parts of the service provider's network (you might have different service providers). Consult with your service provider to determine the requirements for your buildings. Of course, capacity planning for your telephony network might require more than one gateway in each site.
After setting up the gateways to correctly connect to the service provider's network, configure all route patterns used in Chicago's ERLs to use gateway CHI, and all route patterns used in New York's ERLs to use gateway NYC.
To enable phone movement between Chicago and New York, you must also configure an inter-cluster trunk to link the Cisco Unified Communications Manager clusters, and create an inter-Emergency Responder group route pattern so that Emergency Responder can transfer calls between Cisco Unified Communications Manager clusters served by separate Emergency Responder groups. The Create Route Patterns for Inter-Cisco Emergency Responder Group Communications goes into more details about how Emergency Responder handles phone movement in this situation.
As phones move between sites, Emergency Responder dynamically updates their ERLs so that emergency calls get routed out of the desired gateway. However, if the WAN link becomes unavailable, Emergency Responder can not track phone movement between the sites.