Quick Reference Guide

188 PowerConnect B-Series TI24X Configuration Guide
53-1002269-02
Egress buffer thresholds for QoS priorities
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FIGURE 32 Egress buffer thresholds on PowerConnect devices
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 PowerConnect will be able to forward oversubscribed packets instead of dropping them.
Cut-Through Switching Support on PowerConnect B-Series TI24X
Switches
The PowerConnect B-Series TI24X 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 32 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 PowerConnect B-Series TI24X 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.
Level 6
Maximum
Level 2
Minimum
Level 1
Level 3
Level 5
Level 4
Egress Buffer Thresholds