Interlogix ATSx500A Series Installation And Programming Manual page 107

Chapter 3: System functions
When control panel is sending MMS, the heartbeat message is suspended. If this
delay is longer than the supervision period, for example, due sending multiple
MMS, the receiver generates a fault.
Solution: The supervision period in OH receiver should be longer than it can take
to send 10 pictures (VGA) and extended by a time necessary for APN switch.
This period is approximately 7 minutes. Note that weak GSM network conditions
may extend this time.
Advisor Advanced ATSx500A(-IP) Installation and Programming Manual 101