This sets, when acting as an IGMP client, how often in seconds the modem resends an unsolicited membership report for a group it has joined, without being explicitly queried. Periodically resending this report rather than sending it just once at join time guards against the initial report being lost on a satellite link with nonzero packet loss, ensuring the upstream querier still eventually learns this modem wants to remain in the group. Setting this to 10 means the modem resends its join report every 10 seconds for a while after joining, so even if the very first report is lost, a subsequent one within 10 seconds should still register the membership.