What are the network requirements when redundant Cisco Unified ICM servers are geographically distributed?

What are the network requirements when redundant Cisco Unified ICM servers are geographically distributed?

A.
The servers must be connected by a private network card and crossover cables.

B.
The public and private networks must share the same infrastructure.

C.
The servers must be connected by a private dedicated network with each server having a second NIC connected to a dedicated WAN link.

D.
The private network can coexist with the rest of the customer’s corporate network.