# Resiliency Considerations in a Cluster

If you are implementing resiliency within your cluster, it is recommended that you do not locate a secondary controller in a location that is remote to its primary controller, for example, in a distant city or a different country.

If you situate a secondary controller in a remote location, you need to consider the impact on the following features:

- Emergency numbers, for example 911, dialed by an extension user that has failed over to the secondary controller will be routed to the emergency service in the vicinity of the secondary controller. So, if the user is located in Chicago and the secondary is located in New York, a 911 call would be routed to an emergency service provider in New York.

- CESID
  Customer Emergency Service Identification. The CESID is a number that uniquely identifies the device that dialed 911. The CESID is fed into the automatic location identification (ALI) database at the Public Safety Answering Point (PSAP) so that emergency services can be dispatched to the correct location. numbers could be routed to a different emergency service provider.

- External calls placed through the secondary controller could result in long distance charges. For example, if an IP phone user on in Chicago fails over to a secondary controller in New York and then places a call to a destination in Chicago, the call could result in long distance charges.

- Time zone differences will be displayed on the users phones.

Related Topics

- Planning the Cluster

- Cluster Configuration Notes

- Preventing Dialing Conflicts

- Route Optimization