Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 315

Using PFC and ETS to Manage Converged Ethernet Traffic Using PFC and ETS to manage converged ethernet traffic: dcb-map linecard all backplane all dcb-map-name Hierarchical Scheduling in ETS Output Policies ETS supports up to three levels of hierarchical scheduling. For example, you can apply ETS output policies with the following configurations: Priority group 1 Assigns traffic to one priority queue with 20% of the link bandwidth and strictpriority scheduling. Priority group 2 Assigns traffic to one priority queue with 30% of the link bandwidth. Priority group 3 Assigns traffic to two priority queues with 50% of the link bandwidth and strictpriority scheduling. In this example, the configured ETS bandwidth allocation and scheduler behavior is as follows: Therefore, in this example, scheduling traffic to priority group 1 (mapped to one strict-priority queue) takes precedence over scheduling traffic to priority group 3 (mapped to two strict-priority queues). Unused bandwidth Normally, if there is no traffic or unused bandwidth for a priority group, the usage: bandwidth allocated to the group is distributed to the other priority groups according to the bandwidth percentage allocated to each group. However, when three priority groups with different bandwidth allocations are used on an interface: • If priority group 3 has free bandwidth, it is distributed as follows: 20% of the free bandwidth to priority group 1 and 30% of the free bandwidth to priority group 2. • If priority group 1 or 2 has free bandwidth, (20 + 30)% of the free bandwidth is distributed to priority group 3. Priority groups 1 and 2 retain whatever free bandwidth remains up to the (20+ 30)%. Strict-priority groups: If two priority groups have strict-priority scheduling, traffic assigned from the priority group with the higher priority-queue number is scheduled first. However, when three priority groups are used and two groups have strict-priority scheduling (such as groups 1 and 3 in the example), the strict priority group whose traffic is mapped to one queue takes precedence over the strict priority group whose traffic is mapped to two queues. Priority-Based Flow Control Using Dynamic Buffer Method Priority-based flow control using dynamic buffer spaces is supported on the switch. In a data center network, priority-based flow control (PFC) manages large bursts of one traffic type in multiprotocol links so that it does not affect other traffic types and no frames are lost due to congestion. When PFC detects congestion on a queue for a specified priority, it sends a pause frame for the 802.1p priority traffic to the transmitting device. Data Center Bridging (DCB) 315