7–RoCE Configuration
Configuring DCQCN
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Configuring DCQCN
Data Center Quantized Congestion Notification (DCQCN) is a feature that
determines how an RoCE receiver notifies a transmitter that a switch between
them has provided an explicit congestion notification (notification point), and how
a transmitter reacts to such notification (reaction point).
This section provides the following information about DCQCN configuration:
Global Settings on RDMA Traffic
DCQCN Terminology
The following terms describe DCQCN configuration:
ToS
(type of service) is a single-byte in the IPv4 header field. ToS
comprises two ECN least significant bits (LSB) and six Differentiated
Services Code Point (DSCP) most significant bits (MSB). For IPv6, traffic
class is the equivalent of the IPv4 ToS.
ECN
(explicit congestion notification) is a mechanism where a switch adds
to outgoing traffic an indication that congestion is imminent.
CNP
(congestion notification packet) is a packet used by the notification
point to indicate that the ECN arrived from the switch back to the reaction
point. CNP is defined in the Supplement to
InfiniBand Architecture
Specification Volume 1 Release 1.2.1
, located here:
https://cw.infinibandta.org/document/dl/7781
VLAN Priority
is a field in the L2 vLAN header. The field is the three MSBs
in the vLAN tag.
PFC
(priority-based flow control) is a flow control mechanism that applies to
traffic carrying a specific vLAN priority.
