Press Play to hear the narration for this step, or press Next to advance.
0.5×2×1.0×
Step 1/ 1
Step 0 / 0
KNOWLEDGE CHECK
🎉
Lesson complete
🎓
Course complete
You finished all 7 lessons of the GPU Cluster Network Architecture tutorial:
RDMA and RoCEv2 · rail-optimized routing · ECN and DCQCN · PFC · Dragonfly+ DLB · adaptive and Valiant routing.
⚡
GPU platform lab
Pick an accelerator on each side, run the same fabric model on both, and compare network performance and cost
SIDE A — also drives the topology
SIDE B — comparison
A
B
CLUSTER
32 nodes · 256 GPUs
405B parameters
VERDICT
AT A GLANCE
Assumptions.
Ring all-reduce over BF16 gradients; 4M-token global batch; 40% peak MFU;
85% RoCEv2 line-rate efficiency; fabric efficiency 90% rail-optimized, 94% DLB;
70% of compute time available to hide comms behind. 64-port leaves with 32 host
and 32 fabric ports, spine count leaves ÷ 2. $75k per node for CPU, chassis and
storage. Power at $0.10/kWh, PUE 1.3, 3-year window.
Read the comparison, not the absolutes. This models a
naive data-parallel all-reduce over the full gradient set. Real training shards optimiser
state and overlaps far more aggressively, so step times here are an upper bound. The
ratio between two platforms on the same workload is the useful output.
Prices are public street-price estimates and move
constantly — read them as order-of-magnitude, not as a quote. Specs are vendor-published.
📘
How to use this tutorial
GPU cluster fabric — narrated course guide
What this is
A narrated, step-locked course covering two GPU cluster fabric designs: the rail-optimized stripe fabric and the Dragonfly+ DLB fabric. Seven lessons, 30 animated steps, voice narration, and a quiz after each lesson. Expect 50 to 70 minutes end to end.
The screen
Area
What it does
Header
Lesson pills 1 to 7. Green is finished, blue is current. Click a finished pill to revisit that lesson.
Sidebar
Every step in the current lesson. Click any step you have already reached to jump back to it.
Topology
The animated fabric. Devices glow gold when they are carrying the packet, red when their queue is in trouble. The gold banner at the top gives the one-line takeaway.
Packet inspector
The live RoCEv2 header and the switch egress queue. Fields that changed since the last step flash gold, and fields flash again as the narrator names them.
Narration panel
Transcript, play and stop, voice picker, speed from 0.5× to 2×, captions, and the step seek bar.
Working through a step
The topology animates as soon as the step loads.
Read the gold banner for the takeaway, then the transcript below.
Press Play to hear it narrated. Pick a voice and a speed that suit you.
Turn on CC to follow the words as they are spoken. Drag the caption panel anywhere.
Press Next. On the last step the button reads Finish lesson.
Answer the quiz to unlock the next lesson.
Keyboard
Space plays or stops narration. Left and right arrows move between steps.
If you hear nothing
Narration uses your browser's built-in speech engine. Chrome and Edge on desktop have the widest voice selection. Safari needs one click on the page before it will speak. If the voice list is empty, reload the page once the browser has finished loading its voices.