This read-only gauge reports the current received burst size. Unlike the counters around it, this is a live, moment-to-moment measurement of how much burst headroom is currently being consumed against ccarConfigLimit and ccarConfigExtLimit, so it's the value to watch in near-real-time when trying to catch a rate-limit entry in the act of nearly, or actually, triggering the probabilistic drop behavior described under the extended limit. Watching this gauge climb toward the value configured in ccarConfigExtLimit during a traffic spike would confirm that a burst is actively approaching the point where CAR's probabilistic dropping kicks in.