when the optional CAS and on-hook detection features are enabled, the following conditions apply:
The permanent virtual connection (PVC) provisioned for the CES circuit always exists.
The bandwidth for the CES circuit is always reserved.
During an on-hook state, most of the bandwidth reserved for the CES circuit is not in use. (Dummy cells are sent from the ingress node to the egress node to maintain the connection.) Therefore, this bandwidth becomes available for use by other network traffic, such as available bit rate (ABR) traffic.
During an off-hook state, all the bandwidth reserved for the CES circuit is dedicated to that circuit