Establishment of a flexible rate interface link to restore channels from a failed communication link

In a telecommunication switching system having a plurality of switch nodes with each of the switch nodes responsive to a failure of a communication link within a group of communication links to establish a flexible rate interface (FRI) link upon there being no spare channels within the group of communication links and to switch active calls from the channels of the failed communication link to the channels of the newly established FRI link. Advantageously, the group of communication links can be a non-facility access service (NFAS) group. Advantageously, this allows for additional B channels to be added to the NFAS group even though there are no remaining physical communication links between the two switch nodes being interconnected by the NFAS group. The establishment of the FRI link allows for the addition of B channels to the NFAS group with these B channels being routed through other switch nodes of the communication switching system. The FRI link becomes part of the NFAS group and control is provided for the B channels of the FRI link by the primary D channel of the NFAS group. Advantageously, the FRI link can be set up through other communication facilities other than the communication switching system. For example, if the two switch nodes interconnected by the NFAS group are both connected to the public telephone network, the FRI link can be set up through the public telephone network.