Supermicro SSE-F3548S/SSE-F3548SR Configuration User’s Guide
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Each ingress port on the switch has a single receive queue buffer for incoming traffic. When an untagged
frame arrives, it is assigned the value of the port as its port default priority. Tagged frames use the
assigned CoS value when it passes through the ingress port.
9.2.4
Bandwidth Management
Bandwidth limiting is configured at the level of traffic classes. Traffic classes can be assigned minimum
bandwidths, maximum bandwidths, and weights. Weights are used to divide the bandwidth
proportionally among all traffic classes within a QoS policy, in such a way that a traffic class does not
receive more than its maximum bandwidth or less than its minimum bandwidth.
9.3
Port-Based Rate Limit
Rate limits define which packets conform to or exceed the defined rate based on the following two
parameters:
Average rate
determines the average transmission rate. Traffic that falls under this rate will always
conform.
Burst size
specifies in bits (or bytes) per burst how much traffic can be sent within a given unit of time
without causing scheduling concerns. It determines how large a traffic burst can be before it exceeds the
rate limit.
Traffic that exceeds the rate limit is dropped. Supermicro switches support output rate limits.
9.4
HOLBlocking Prevention
Supermicro switches provide eight egress queues per port. Each queue has a dynamic packet limit based
on the availability of packet buffer memory. When a switch receives packets at a fast rate destined to a
particular egress port, its egress port queuesbecome filled up. When the egress queue is full, all packets at
ingress are dropped. This phenomenon of dropping ingress packets due to egress port/CoS queue over-
subscriptionis called Head of Line (HOL) blocking.
Supermicro switches provide support to prevent HOL blocking. When HOL blocking prevention is enabled
in the switch, itdropspackets newly arriving on the ingress if they aredestined to an oversubscribed egress
port, based on the egress queue threshold. The switch stops dropping ingress packets once it determines
the egress queue is not over-subscribed by using specific counters and thresholds. This mechanism
ensures fair access to all port buffers.
HOL blocking prevention provides lossy buffer management, however it improves overall system
throughput.
9.5
Enabling QoS
QoS is disabled by default in Supermicro switches. Follow the below steps to enable QoS.
Step Command
Description
Step 1
configure terminal
Enters the configuration mode
Step 2
set qos enable
Enables QoS on all interfaces
Step 3
End
Exits the configuration mode