This read-only object reports the value of sysUpTime at the moment this BUS became enabled. Because this is a sysUpTime snapshot rather than a duration, computing how long the BUS has actually been up requires subtracting this value from the current sysUpTime, and a value that keeps advancing on repeated polls, rather than staying fixed, is itself a symptom that the BUS keeps restarting rather than staying continuously enabled. A BUS whose busUpTime value changes every few minutes across successive polls indicates it's repeatedly reinitializing, likely due to something like an address mismatch with the switch or a connectivity flap.