A method and mechanism to detect failure of an S102 link between an Evolved Packet Core, EPC, network based Mobility Management Entity, MME, and an Interworking System, IWS, in a Mobile Switching Center, MSC, pool deploying Circuit Switched Fallback, CSFB, for the EPC network. A heartbeat message exchange between an MME-IWS pair augments the current standards to provide a simple and direct method to monitor the application layer status of the S102 link between the EPC-based MME and the MSC pool-based IWS. Upon detecting a link failure, message flows can be quickly re-routed to another S102 link or MSC. Reverse use of an A21 Event Notification message from an IWS to MME, or a re-assigned IWS's delayed acknowledgement of an initial call-related message from an MME also augment the current standards to address IWS relocation related message-bouncing in MSC pool-based deployments of CSFB, thereby allowing efficient routing of messages.