With IPHost Network Monitor you can run simple snmp requests against a Fortinet device in your network.
fgApSIPClientReg
fg Ap SIP Client Registration
1.3.6.1.4.1.12356.101.10.106.3.1.1
Number of client registration requests (Register and Options) in this virtual domain processed by the SIP proxy since start-up
Back to FORTINET-FORTIGATE-MIB MIB page.
IPHost Network monitor allows you to monitor fgApSIPClientReg on Fortinet device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Fortinet firewalls right now.