QoS and QoS Policies
54
Quality of Service Guide
3HE 11014 AAAC TQZZA Edition: 01
3.1.11 QoS for Gen-3 Adapter Cards and Platforms
Third-generation (Gen-3) Ethernet adapter cards and Ethernet ports on Gen-3
platforms support 4-priority scheduling.
The main differences between Gen-3 hardware and Gen-1 and Gen-2 hardware are
that on Gen-3 hardware:
• SAPs are shaped (that is, no unshaped SAPs)
• SAPs and VLANs are shaped by 4-priority schedulers, not 16-priority schedulers
• 4-priority scheduling is done on a per-SAP basis
• backpressure is applied according to relative priority across VLANs and
interfaces. That is, scheduling is carried out in priority order, ignoring per-VLAN
and per-interface boundaries. Conforming, expedited traffic across all queues is
scheduled regardless of the VLAN boundaries. After all the conforming,
expedited traffic across all queues has been serviced, the servicing of
conforming, best effort traffic begins.
See Scheduling Modes for a summary of scheduler mode support. For information
on adapter card generations, refer to the “Evolution of Ethernet Adapter Cards,
Modules, and Platforms” section in the 7705 SAR Interface Configuration Guide.
Note:
• From Release 7.0.R6, schedulers on Gen-3 adapter cards and platforms have been
updated to better align with the scheduling behavior supported on the 7705 SAR
adapter cards and platforms. The updated scheduler mode is called “4-priority”
scheduler-mode throughout the CLI. Prior to Release 7.0.R6, the CLI designation was
“4-priority-hqos”.
• In the updated mode of operation, arbitration among different flows at the second-tier
aggregate (per-SAP or per-VLAN) and third-tier aggregate (per-customer (MSS))
levels are carried out in a round-robin manner, and scheduling is done on a per-SAP
basis.
Caution: Any Gen-3 adapter card or platform running Release 7.0.R6 or later software uses
4-priority scheduling instead of 4-priority-hqos scheduling, which was supported previously.
The migration of scheduler mode is automatic with an upgrade and there is no operator
action required. As part of the migration, all CIR values at second-tier (per-SAP and
per-VLAN) and third-tier (per-customer (MSS)) aggregate shaper levels are set to zero.
Operators must exercise caution when performing an upgrade to Release 7.0.R6 or later
from a previous Release 7.0 version, and must adjust the affected CIR values in accordance
with the needs of their applications as soon as possible. The shapers with affected CIR
values are listed later in this section.
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