Which three steps configure Cisco Unified Survivable Remote Site Telephony for SIP phones? (Choose three.)
A. Configure voice register pool.
B. Configure voice register global dn.
C. Configure an SRST reference.
D. Configure a phone NTP reference.
E. Configure the SIP registrar.
F. Configure telephony service.
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cusrst/admin/sccp_sip_srst/configuration/guide/SCCP_and_SIP_SRST_Admin_Guide/srst_setting_up_using_sip.html
Reference here.