What does PFC do on a RoCE network?
Why D is the answer
Pauses one priority to prevent drops
Priority flow control pauses a class rather than the whole link.
In detail
- PFC pauses one priority to prevent drops.
- Only that class pauses.
Use case
An illustrative scenario, not a real incident.
A queue nears full, and PFC pauses that priority, so nothing is dropped.
See it in different ways
flowchart LR A["RoCE traffic"] --> B["QoS class"] B --> C["ECN signals congestion"] C --> D["PFC prevents drops"] D --> E["Adaptive routing spreads load"]
sequenceDiagram participant S as Sender participant W as Switch participant R as Receiver S->>W: RDMA traffic W->>R: Marks packets with ECN R-->>S: Congestion notification S->>S: Slows down W-->>S: PFC pause, if a queue fills
stateDiagram-v2 state "Flowing" as s0 state "Paused" as s1 [*] --> s0 s0 --> s1: queue filling s1 --> s0: queue drains
Key point: PFC pauses one priority.
Why the other options are wrong
- A. Marks packets to report congestion to the sender
- That is ECN.
- B. Chooses the shortest path through the fabric
- That is routing.
- C. Compresses traffic to fit a slower link
- It does not compress.