QoS and QoS Policies
36
Quality of Service Guide
3HE 11014 AAAC TQZZA Edition: 01
Note:
1. The 7705 SAR-X has three buffer pools. Each block of ports (MDA) has its own buffer pool.
3.1.6.3.1 Advantages of Buffer Chaining
Buffer chaining offers improved efficiency, which is especially evident when smaller
packet sizes are transmitted. For example, to queue a 64-byte packet, a card with a
fixed buffer of 2304 bytes allocates 2304 bytes, whereas a card with a fixed buffer of
512 bytes allocates only 512 bytes. To queue a 1280-byte packet, a card with a fixed
buffer of 2304 bytes allocates 2304 bytes, whereas a card with a fixed buffer of 512
bytes allocates only 1536 bytes (that is, 512 bytes × 3 buffers).
3.1.7 Per-SAP Aggregate Shapers (H-QoS) On Gen-2
Hardware
This section contains overview information as well as information on the following
topics:
• Shaped and Unshaped SAPs
• H-QoS Example
This section provides information on per-SAP aggregate shapers for Gen-2 adapter
cards and platforms. For information on Gen-3 adapter cards and platforms, see QoS
for Gen-3 Adapter Cards and Platforms.
Hierarchical QoS (H-QoS) provides the 7705 SAR with the ability to shape traffic on
a per-SAP basis for traffic from up to eight CoS queues associated with that SAP.
On Gen-2 hardware, the per-SAP aggregate shapers apply to access ingress and
access egress traffic and operate in addition to the 16-priority scheduler, which must
be used for per-SAP aggregate shaping.
The 16-priority scheduler acts as a soft policer, servicing the SAP queues in strict
priority order, with conforming traffic (less than CIR) serviced prior to non-conforming
traffic (between CIR and PIR). The 16-priority scheduler on its own cannot enforce a
traffic limit on a per-SAP basis; to do this, per-SAP aggregate shapers are required
(see H-QoS Example).
The per-SAP shapers are considered aggregate shapers because they shape traffic
from the aggregate of one or more CoS queues assigned to the SAP.
To Next Page
Loading...
