Quality of Service Guide QoS and QoS Policies
Edition: 01 3HE 11014 AAAC TQZZA 89
The ingress buffers for a card are much larger than the ingress buffers for the fabric;
therefore, it is advantageous to use the larger card buffers for ingress shaping. In
order to use the ingress card buffers and have much more granular control over
traffic, two fabric profile modes are supported, per-destination mode and aggregate
mode. Both modes offer shaping towards the fabric from an adapter card, but
per-destination shapers offer the maximum flexibility by precisely controlling the
amount of traffic to each destination card at a user-defined rate. Aggregate mode is
used for simpler deployments, where the amount of traffic flowing to a destination
adapter card is not controlled.
The default mode of operation for the 7705 SAR is set to aggregate, and the fixed
aggregate rate of 200 Mb/s is set for both access ingress and network ingress traffic.
Therefore, in a default configuration, each adapter card can switch up to 200 Mb/s of
access ingress and network ingress traffic towards the fabric.
All the switched traffic can be destined for a single adapter card or it can be spread
among multiple adapter cards. For higher-bandwidth applications, a network traffic
analysis is recommended to determine which shaper rates would best suit the
application and traffic patterns of a particular environment.
The to-fabric shapers are provided on the 7705 SAR to ensure adequate use of
ingress buffers in case of congestion. With the ingress shapers, the large ingress
card buffers can be configured to absorb bursty traffic and pace the traffic for better
use of resources.
For example, if the average access ingress traffic bandwidth for an adapter card is
400 Mb/s and the peak bandwidth is 800 Mb/s, the rate of the to-fabric shapers can
be configured to be 400 Mb/s. This allows the bursty ingress traffic to be paced by
absorbing the bursty traffic after being shaped at 400 Mb/s. The initial burst is
absorbed at the adapter card where the bursty traffic ingresses the 7705 SAR. The
ingress buffers are used to absorb the burst and the fabric buffers are not exhausted
by any single adapter card. The same example applies to network ingress traffic.
Table 9 summarizes the different capabilities offered by the two modes.
Table 9 Fabric Profile Modes Options and Capabilities
Capability Per Destination Mode Aggregate Mode
Access ingress to-fabric shapers ✓✓
Network ingress to-fabric shapers ✓✓
Individual shaping from an ingress card
towards each destination card based on a
user-defined rate
✓
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