Brocade TurboIron 24X Series Configuration Guide - Manual (Page 303)

Brocade TurboIron 24X Series Configuration Guide 269
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Egress buffer thresholds for QoS priorities
FIGURE 6 Egress buffer thresholds
Manually increasing buffer thresholds may be useful in situations where applications have
intermittent bursts of oversubscription. For example, by increasing a port egress buffer threshold,
the device will be able to forward oversubscribed packets instead of dropping them.
Cut-Through Switching Support
The device operates in cut-through switching mode, meaning it starts forwarding a frame even
before the whole frame has been received. However, if there is any oversubscription on the egress
port, either due to speed mismatch (10-Gbps to 1-Gbps) or network topology (traffic from two
10-Gig ports going out of one 10-Gig port), the switch will buffer the packets and the forwarding
behavior will be similar to store-and-forward mode.
Cut-Through Switching Mode and CRC Error Packet Handling
In the cut-through switching mode, if a packet is detected with a CRC error, the whole packet will be
dropped if the packet size is less than or equal to 384 bytes. If the packet size is larger than 384
bytes, the last few bytes will be trimmed off the frames.
Default settings for egress buffer thresholds
Figure 6 illustrates the egress buffer threshold levels. For both non-jumbo and jumbo frame
forwarding, the default egress buffer threshold is level-4 for all QoS priorities.
The device is automatically configured to use the default thresholds for egress buffers. If you want
to change the default threshold values, you must first disable the default values. The next section
shows how.
Disabling and re-enabling the default settings
for egress buffer thresholds
To disable the device from using the default settings for egress buffer thresholds, enter the
following command.
Level 6
Maximum
Level 2
Minimum
Level 1
Level 3
Level 5
Level 4
Egress Buffer Thresholds