PFC PAUSE Frame Forwarded Transparently in Wide Area Networks#

Xiaoming He (China Telecom), Lijie Deng (China Telecom).

• Why: AI and distributed-storage workloads now run RDMA across metro/wide-area links between data centers; the draft's argument is that AIDC interconnect needs lossless WAN transmission, and hop-by-hop PFC in the WAN is both costly and amplifies head-of-line blocking, deadlock and congestion diffusion.
• What: China Telecom's proposal to carry PFC PAUSE frames transparently across the WAN: the egress PE validates the PFC frame (destination MAC must be 01-80-C2-00-00-01, source must be the directly-connected DC gateway port), encapsulates it in the DCI tunnel (SRv6, SR-MPLS, or VXLAN), and transit nodes forward it untouched; the ingress PE decapsulates, rewrites the source MAC to its own port, and delivers it to the source DC gateway. End-to-end flow control with zero PFC capability required in WAN nodes.
• How: The price is buffering: the destination DC gateway must reserve Buffer > (R − T) × D per priority queue, where D is the PFC propagation delay across the WAN — the draft's key engineering constraint.
• Where applicable: DCI/MAN interconnect of two AIDCs under one administrative intent. Individual draft -00; competing with the SRv6 approach below for the same problem.