[SR-Users] Get registered user list

[Никита Лебедев]

Good day! Can anyone point me to right direction? The question is  - I
want to get list of registered users (to find out who is online at the
moment) from sip server. I'm using kamailio on server side and exosip
library on client side.

I tried   to find something in  RFC 3261 and failured... Can someone
help and tell what to do or where to look for the answer?