The standard accounting mechanism uses ‛packet-based’ rules that account for the DLC header, any existing tags, Ethernet payload, and the 4-byte CRC. The Ethernet framing overhead that includes the Inter-Frame Gap (IFG) and preamble (20 bytes total) are not included in packet-based accounting. When frame-based accounting is enabled, the 20-byte framing overhead is included in the queue or policer CIR, PIR, and scheduling operations, allowing the operations to take into consideration on-wire bandwidth consumed by each Ethernet packet.
Because the native queue accounting functions (stats, CIR, and PIR) are based on packet sizes and do not include Ethernet frame encapsulation overhead, the system must manage the conversion between packet-based and frame-based accounting. To accomplish this, the system requires that a policer or queue operates in frame-based accounting mode, and must be managed by a virtual scheduler policy or by a port virtual scheduler policy. Egress policers or queues can use either port or service schedulers to accomplish frame-based accounting, but ingress queues are limited to service-based scheduling policies.
Turning on frame-based accounting for a policer or queue is accomplished through a frame-based accounting command defined on the scheduling policy level associated with the policer or queue or through a policer or queue frame-based accounting parameter on the aggregate rate limit command associated with the queues SAP, multiservice site or subscriber or multiservice site context. Packet byte offset settings are not included in the applied rate when frame-based accounting is configured, however the offsets are applied to the statistics.