The diagram below hows a network scenario of calls involving PSTN/IP and the flow of call detail records (CDRs) in the VX system. This is a typical scenario but many other possibilities may be configured. The diagram shows the ingress and egress gateways each sending one CDR per call. Note that there is no concept of call legs in this system. If there is an integrated voice response (IVR) session on the ingress side, one CDR is sent for every call.