This is a 64-bit counter of multicast bytes (octet count) delivered up from the ring into the router's own higher-layer stack, specifically the high-priority portion of that traffic, per SRP's two-level QoS scheme, measured over one specific, already-completed 15-minute bucket from the rolling 24-hour history, rather than a live count. Because this is measured on the host side, it reflects only traffic this specific router is locally sourcing or sinking, so comparing it against the Ring-side counters on the same box shows how much of what crosses the ring this node actually originates versus just passes through, SRP's high-priority class is always serviced ahead of low-priority traffic when the ring is congested, so a rising trend here at the expense of the matching low-priority counter is a sign that latency-sensitive traffic is starting to crowd out best-effort traffic on this ring, and because multicast frames on a shared ring get passed along until they're stripped off or time out, a sudden multicast surge here more often reflects a flooding condition (e.g. an ARP-like storm or a new multicast subscriber group) than ordinary point-to-point application growth, and pairing this byte count with the matching packet counter for the same traffic class is how you'd derive the average frame size and the actual bit rate that class is consuming. For instance, this counter might read roughly 610,026,872 bytes of multicast traffic over that window, which combined with the matching packet counter lets you compute an average frame size for that class.