China Mobile China Mobile Centec Centec Centec Inesa SAIA Network measurement and telemetry systems that collect data at multiple points along a path or across multiple targets require a means to correlate the collected data. When each collection point independently selects which packets to observe, the resulting data sets may not overlap, preventing per-packet correlation of measurements across points. This document specifies how source-directed selection -- where a single node determines which packets are subject to measurement and signals this to other nodes -- achieves correlated data collection across multiple points. Two applications are described: IOAM Direct Export for in-band network telemetry, and PTP Sequence ID range assignment for multi-slave time synchronization.