This sets how often the two chassis exchange ICL heartbeat frames to detect link failure, tunable from 1 to 30 seconds with a default of 1 second. A shorter interval, the 1-second default, gives faster failure detection at the cost of more control-plane overhead, so an admin might lengthen it slightly on a very busy chassis pair to reduce CPU load, trading off detection speed. Setting this to 5 would mean the chassis pair takes roughly five times as long to notice a lost heartbeat compared to the default.