This tunes IGMP robustness to account for possible packet loss on the network, per ITU-T G.988 9.3.27; the recommended default of 0 makes the ONU follow RFC 3376 and copy the robustness value from query messages received further upstream instead of using a fixed value. Admins raise it on lossy access networks to make IGMP state more resilient to dropped messages, at the cost of slightly slower leave processing. For example, increasing robustness reduces the chance a single lost IGMP query causes a subscriber to briefly lose a multicast stream.