QoS and QoS Policies
86
Quality of Service Guide
3HE 11014 AAAC TQZZA Edition: 01
3.2.5 Ingress Shaping to Fabric (Access and Network)
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 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, 7705 SAR-W, 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.
3.2.5.1 BMU Support
Fabric shapers support both unicast and multipoint traffic. Multipoint traffic can be
any combination of broadcast, multicast, and unknown (BMU) frames. From access
ingress to the fabric, BMU traffic is treated as unicast traffic. A single copy of BMU
traffic is handed off to the fabric, where it is replicated and sent to all potential
destination adapter cards.
Note: The CLI does not block a fabric profile with an unshaped SAP CIR configuration on
an 8-port Ethernet Adapter card, a 6-port Ethernet 10Gbps Adapter card, an ASAP card
(16-port T1/E1 ASAP Adapter card or 32-port T1/E1 ASAP Adapter card). However, the
unshaped SAP CIR configuration has no effect and is ignored on these cards.
Note: 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.
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