OC-IM-CallReferenceNumber header is a custom SIP header used by Sentinel VoLTE SCC-AS to send the Call Reference Number
to the IM-SSF to use in future messages.
The header name is
OC-IM-CallReferenceNumber and its value is a string representing the 8 bytes of the call reference number
in Hexadecimal format.
The header does not have any special parameters.
The header is set by the FetchMSRN Feature.