Dell PowerSwitch S4820T 9.50.1 Configuration Guide for the S4820T System - Page 310
Priority-Based Flow Control Using Dynamic Buffer Method, Pause and Resume of Traffic
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Step 5 6 Task Apply the DCB map, created to disable the PFC operation, on the interface Command dcb-map {name | default} Configure the port queues that still function pfc no-drop as no-drop queues for lossless traffic. For the dot1p-queue assignments. queuesqueue-range The maximum number of lossless queues globally supported on a port is 2. You cannot configure PFC no-drop queues on an interface on which a DCB map with PFC enabled has been applied, or which is already configured for PFC using the pfc priority command. Range: 0-3. Separate queue values with a comma; specify a priority range with a dash; for example: pfc no-drop queues 1,3 or pfc no-drop queues 2-3 Default: No lossless queues are configured. Command Mode INTERFACE INTERFACE Priority-Based Flow Control Using Dynamic Buffer Method Priority-based flow control using dynamic buffer spaces is supported on the S4820T platform. 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. Pause and Resume of Traffic The pause message is used by the sending device to inform the receiving device about a congested, heavily-loaded traffic state that has been identified. When the interface of a sending device transmits a pause frame, the recipient acknowledges this frame by temporarily halting the transmission of data packets. The sending device requests the recipient to restart the transmission of data traffic when the congestion eases and reduces. The time period that is specified in the pause frame defines the duration for which the flow of data packets is halted. When the time period elapses, the transmission restarts. When a device sends a pause frame to another device, the time for which the sending of packets from the other device must be stopped is contained in the pause frame. The device that sent the pause frame empties the buffer to be less than the threshold value and restarts the acceptance of data packets. Dynamic ingress buffering enables the sending of pause frames at different thresholds based on the number of ports that experience congestion at a time. This behavior impacts the total buffer size used by a particular lossless priority on an interface. The pause and resume thresholds can also be configured dynamically. You can configure a buffer size, pause threshold, ingress shared threshold weight, and resume threshold to control and manage the total amount of buffers that are to be used in your network environment. 310 Data Center Bridging (DCB)
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