There are two different mechanisms in Sentinel to create CDRs depending on the Sentinel Service:
Sentinel SIP writes CDRs as a collection of Diameter AVPs, with the underlying AVP protocol buffer format being defined in Sentinel core. The actual job of creating and writing CDRs is accomplished by the AVP CDR feature.
Sentinel Diameter and Sentinel SS7 write CDRs as part of their respective services, and use Mappers to assemble their contents.
Consequently the approach to customising CDR writing differs based on which Service the CDRs should be customised for. The following pages describe each approach in detail.