For a Centralized Attendant Service (CAS), main system calls from a branch will be processed if the Media Gateways under the control of the survivable core server contain the incoming trunks and attendant consoles.

For a CAS Branch, calls are routed as if Night Service mode was activated. Calls are routed only if the trunks to the CAS Main are under control of the survivable core server controlling the media gateway where attendant seeking calls arrive for service.