https://mktry.com/posts/ Recent content in Posts on Packet Catcher Hugo en Fri, 10 Apr 2026 08:00:00 +0800 https://mktry.com/posts/pfc-headroom-test-with-snappi/ Fri, 10 Apr 2026 08:00:00 +0800 https://mktry.com/posts/pfc-headroom-test-with-snappi/ <h2 id="background">Background</h2> <p>In data center networks, <strong>Priority Flow Control (PFC)</strong> is a mechanism defined in IEEE 802.1Qbb that allows a receiver to pause traffic on a per-priority basis, enabling lossless transport for high-priority traffic such as RDMA over Converged Ethernet (RoCE).</p> <p>When a switch&rsquo;s ingress buffer starts filling up, it sends a <strong>PFC PAUSE frame</strong> to the upstream sender. However, there is always some in-flight traffic between the time the PAUSE is sent and when the sender actually stops — this in-flight data must be absorbed by the <strong>headroom buffer</strong>.</p>