After the traffic is scheduled, it must be sent to the fabric interface. In order to avoid congestion in the fabric and ease the effects of possible bursts, a shaper is implemented on each adapter card.
The shapers smooth out any packet bursts and ease the flow of traffic onto the fabric. The shapers use buffer space on the adapter cards and eliminate the need for large ingress buffers in the fabric.
The ingress to-fabric shapers are user-configurable. For the 7705 SAR-8 Shelf V2 and the 7705 SAR-18, the maximum rate depends on a number of factors, including platform, chassis variant, and slot type. See Configurable Ingress Shaping to Fabric (Access and Network) for details. For the 7705 SAR-M, 7705 SAR-H, 7705 SAR-Hc, 7705 SAR-A, 7705 SAR-Ax, and 7705 SAR-Wx, the shapers can operate at a maximum rate of 5 Gb/s. For the 7705 SAR-X, the shapers are not user-configurable. See Fabric Shaping on the Fixed Platforms (Access and Network) for details.
After the shaping function, all of the traffic is forwarded to the fabric interface in round-robin fashion, one packet at a time, from every access ingress adapter card.
Starting with Release 8.0.R4, unless per-service-hashing is enabled, a 4-byte hash value will be appended to internal overhead for VPLS multicast traffic at ingress. The egress internal hash value is discarded at egress before scheduling. Therefore, shaping rates at access and network ingress and for fabric policies may need to be adjusted accordingly. In addition, the 4-byte internal hash value may be included in any affected statistics counters.