Question

In a lossless Ethernet environment, what does the Priority Flow Control (PFC) mechanism specifically prevent during periods of high congestion?

Accepted Answer

Priority Flow Control specifically prevents packet loss caused by buffer overflow during periods of high congestion. In a standard Ethernet network, when a switch receives more data than its internal memory or buffer can hold, it drops the excess packets. Priority Flow Control is a mechanism that operates at the Data Link Layer, which is the second layer of the OSI networking model, to stop this loss. It works by sending a pause frame to the transmitting device, instructing it to temporarily stop sending data for a specific traffic class. A traffic class is a category of data marked by a priority code in the Ethernet frame header, allowing the network to distinguish between critical traffic and standard traffic. By pausing only the congested traffic flow while allowing other prioritized traffic to continue, the network prevents the switch buffers from becoming overwhelmed. This creates a lossless environment where no data is discarded due to congestion, ensuring that the sender holds the data until the switch has enough buffer space to receive it again.

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In a lossless Ethernet environment, what does the Priority Flow Control (PFC) mechanism specifically prevent during periods of high congestion?