An IGMP proxy-capable switch starts a timer for each (S, G) entry. A multicast source lifetime is the timeout period of an (S, G) entry generated by the IGMP proxy-capable switch.
The IGMP proxy-capable switch starts a timer upon receiving the first multicast data packet for group G from source S. The switch resets the timer each time it receives a multicast packet sent from source S. If the switch does not receive any multicast packet from source S within the lifetime of the source S, the switch determines that source S has stopped sending multicast data to group G and the (S, G) entry has become invalid.