Priority-Based Flow Control Using Dynamic Buffer Method; Pause And Resume Of Traffic; Buffer Sizes For Lossless Or Pfc Packets - Dell C9000 Series Networking Configuration Manual

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.

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.

Buffer Sizes for Lossless or PFC Packets

You can configure up to a maximum of 4 lossless (PFC) queues. By configuring 4 lossless queues, you can
configure 4 different priorities and assign a particular priority to each application that your network is used to
process. For example, you can assign a higher priority for time-sensitive applications and a lower priority for
other services, such as file transfers. You can configure the amount of buffer space to be allocated for each
priority and the pause or resume thresholds for the buffer. This method of configuration enables you to
effectively manage and administer the behavior of lossless queues.
Although the system contains 12 MB of space for shared buffers, a minimum guaranteed buffer is provided to
all the internal and external ports in the system for both unicast and multicast traffic. This minimum
guaranteed buffer reduces the total available shared buffer to 9.5 MB. This shared buffer can be used for lossy
and lossless traffic.
Data Center Bridging (DCB) 337