The Collective That Runs Every Step
AllReduce on the wire — ring mechanics, why it's bandwidth-optimal, the simultaneous-flow pattern your fabric has to handle, and the other collectives you'll meet at scale.
Communication Libraries
The software layer that produces AI traffic. NCCL, RCCL, oneCCL — the libraries every training framework calls. Ring AllReduce mechanics, AllGather, ReduceScatter, AllToAll, NCCL channels, and how to read NCCL_DEBUG output.