Dell S4048T, Configuration Manual

Page: 308 / 1277

Step Task Command Command Mode
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.
Priority-Based Flow Control Using
Dynamic Buffer Method
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.
Data Center Bridging (DCB) 308