Iu: send RANAP CommonID to known connection
An RNC can be a unique reference number told (usually the IMSI) to recognize connection across CS/PS. The RNC can use this information to send paging requests over a present connection.
CommonID should be send as soon an connection is identified e.g. RAU / Attach Request. As soon a SecurityCommand Complete has been validated, the IMSI can be sent.
OS#3920 has a trace where this is happening.