Every 10,000 busy hour call attempts (BHCA) in the cluster requires 900 kbps of bandwidth for Intra-Cluster Communication Signaling (ICCS). This is a minimum bandwidth requirement, and bandwidth is allocated in multiples of 900 kbps.
In addition to the real-time ICCS bandwidth, intra-cluster bandwidth is required for the SQL, CTI Manager, and LDAP traffic. The amount of additional bandwidth is dependant on the use of the system.
Signalling or Control Plane traffic requires additional bandwidth as well.
A maximum Round Trip Time (RTT) of 40 ms is allowed between any two servers in the Cisco CallManager cluster. This time equates to a 20 ms maximum one-way delay, or a transmission distance of approximately 3000 km under ideal conditions.
