Congestion in an NVIDIA Spectrum-X system is evaluated by monitoring the occupancy of its egress queues. When the rate of incoming traffic destined for an output port exceeds the port's transmission capacity, packets begin to accumulate in the egress buffer, increasing the queue load. NVIDIA Spectrum switches provide advanced, real-time telemetry to analyze these queue loads. This information is fundamental for the platform's congestion control mechanisms, such as Explicit Congestion Notification (ECN), which marks packets based on queue depth thresholds to signal impending congestion to endpoints, thereby preventing packet loss and maintaining low-latency, high-throughput performance for AI and HPC workloads.

A. Physical distance between devices primarily affects propagation delay (latency), not network congestion, which is caused by traffic volume exceeding buffer or link capacity.

B. CPU and power usage are metrics for the switch's control plane and hardware health, not a direct measure of data plane traffic congestion in the network fabric.

C. The number of connected devices indicates the network's scale but does not reflect the real-time traffic load or the state of congestion on any specific link.

1. NVIDIA What Just Happened (WJH) Streaming Telemetry Technical Brief (PB-07860-001v02): Page 2, under the "What Just Happened" section, lists common reasons for packet drops that the feature can identify. One of the primary reasons listed is "Egress queue drop: Packet dropped due to full egress queue." This directly confirms that egress queue load is the critical metric for identifying and evaluating congestion.

2. NVIDIA Spectrum Ethernet Switch with NVIDIA Cumulus Linux Datasheet (DS-07998-001v08): Page 2, under "Advanced Congestion Control," states, "Spectrum provides a robust and scalable end-to-end congestion control mechanism that helps to avoid network congestion." These mechanisms, like ECN, operate by monitoring queue buffer occupancy to proactively manage traffic flow.

3. NVIDIA Spectrum-X Networking Platform White Paper (WP-10734-001v1.1): Page 6, in the section "End-to-End Congestion Control," explains that Spectrum-X implements mechanisms to prevent congestion collapse in large-scale AI clusters. It details how the platform "provides fine-grained and accurate congestion information from the network to the endpoints," which is derived from the switch's internal buffer and queue states.