Class of Service

Priority-based flow control X-ON Threshold and per-queue alpha support (QFX5220)—The priority-based flow control (PFC) X-ON threshold is the ingress port's priority group (PG) shared buffer limit. At this limit, the ingress port's peer resumes transmission of packets after a brief PAUSE because of the PFC message sent by this ingress port. You can tune globally the limit of buffers that each queue can consume from the shared pool based on the dynamic threshold setting called the alpha value. Starting with Junos OS Evolved 22.3R1 on QFX5220 devices, you can fine tune the X-ON threshold through the congestion notification profile (CNP) and fine tune the alpha value on a per-queue basis through a scheduler.

[See xon (Input Congestion Notification) and buffer-dynamic-threshold .]