This sets the count threshold of egress buffer overflow events for VBR1 traffic that, within its alert period, triggers a threshold-crossing alert on this port. This threshold on this specific port is what converts VBR1-class congestion on the egress buffer into an actionable alert, letting the admin distinguish overflow severity for this particular service class from the separately-thresholded CBR, ABR, and VBR2 classes sharing the same physical port. A lower threshold here than for VBR2 on this port would reflect that VBR1 is provisioned as the higher-priority variable-rate class and any sustained overflow affecting it warrants earlier attention.