8.3.17.0 - Force10 Networks

How Enhanced Transmission Selection is Implemented
Enhanced transmission selection (ETS) provides a way to optimize bandwidth allocation to outbound
802.1p classes of converged Ethernet traffic. Different traffic types have different service needs. Using
ETS, groups within an 802.1p priority class are auto-configured to provide different treatment for traffic
with different bandwidth, latency, and best-effort needs.
For example, storage traffic is sensitive to frame loss; interprocess communication (IPC) traffic is
latency-sensitive. ETS allows different traffic types to coexist without interruption in the same converged
link.
Note: The IEEE 802.1Qaz, CEE, and CIN versions of ETS are supported.
ETS is implemented on an Aggregator as follows:
• Traffic in priority groups is assigned to strict-queue or WERR scheduling in an ETS output policy and
is managed using the ETS bandwidth-assignment algorithm. FTOS de-qeues all frames of
strict-priority traffic before servicing any other queues. A queue with strict-priority traffic can starve
other queues in the same port.
• ETS-assigned bandwidth allocation and scheduling apply only to data queues, not to control queues.
• FTOS supports hierarchical scheduling on an interface. FTOS control traffic is redirected to control
queues as higher priority traffic with strict priority scheduling. After control queues drain out, the
remaining data traffic is scheduled to queues according to the bandwidth and scheduler configuration
in the ETS output policy. The available bandwidth calculated by the ETS algorithm is equal to the link
bandwidth after scheduling non-ETS higher-priority traffic.
• By default, equal bandwidth is assigned to each port queue and each dot1p priority in a priority group.
• By default, equal bandwidth is assigned to each priority group in the ETS output policy applied to an
egress port. The sum of auto-configured bandwidth allocation to dot1p priority traffic in all ETS
priority groups is 100%.
• dot1p priority traffic on the switch is scheduled according to the default dot1p-queue mapping. dot1p
priorities within the same queue should have the same traffic properties and scheduling method.
• A priority group consists of 802.1p priority values that are grouped together for similar bandwidth
allocation and scheduling, and that share the same latency and loss requirements. All 802.1p priorities
mapped to the same queue should be in the same priority group.
• By default:
— All 802.1p priorities are grouped in priority group 0.
— 100% of the port bandwidth is assigned to priority group 0. The complete bandwidth is
equally assigned to each priority class so that each class has 12 to 13%.
• The maximum number of priority groups supported in ETS output policies on an interface is equal
to the number of data queues (4) on the port. The 802.1p priorities in a priority group can map to
multiple queues.
• A DCB output policy is created to associate a priority group with an ETS output policy with
scheduling and bandwidth configuration, and applied on egress ports.
• The ETS configuration associated with 802.1p priority traffic in a DCB output policy is used in
DCBX negotiation with ETS peers.
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