esaProbeCOSType is a read-create value specifying the first Class of Service a Y.1731/SLM-SLR probe measures, and it has no meaning once esaProbeMultiCOSEnabled turns on multiple COS levels. An administrator sets this to pin a single-COS probe to the traffic class that actually matters for that customer's SLA, such as voice versus best-effort. For example, setting this to a voice-priority COS ensures the probe's delay and jitter numbers reflect the class of traffic the customer is actually paying for low latency on, not an unrelated best-effort queue.