This sets the alert period, in minutes, over which this port evaluates egress buffer overflow events affecting its VBR1 (variable bit rate, class 1) traffic before declaring a threshold-crossing alert. Having a separate alert period specifically for the VBR1 class on this specific port lets the admin tune sensitivity differently for that traffic tier compared to CBR, ABR, or VBR2, reflecting VBR1's own distinct burst tolerance and priority relative to the port's other three service classes. A port carrying premium variable-bit-rate video traffic mapped to VBR1 might use a shorter alert period here than the port's VBR2 setting, to catch overflow conditions affecting that premium traffic more quickly.