Gregory's ServerIndeed @lobingera, the idea can be traced back to an infamous meeting in Quantico VA in 1993. But from 1996 all backdoor requirements originated in Sophia Antipolis, France. The technical specifications are produced by this ITU group called 3GPP SA3LI. Here are their latest doqs from July
https://portal.3gpp.org/ngppapp/TdocList.aspx?meetingId=35178
@harkank @Mer__edith latest CRs ... standardization has some bureocratic overhead.
And itu and 3pgg have different agenda, you are simplifying here
Disclosure: in my dayjob my org's name contains "standardization" and SA3's job is more than LI... (in case you wonder: my work is in RAN 1/2/3/4)