S1f13

S1F13/S1F14 is the SECS-II message pair that establishes communications between a host and equipment for the first time in a session, sent before any other GEM traffic is allowed to flow — it is literally the handshake that turns a connected-but-silent link into an active SECS/GEM communication session. S1F13 (Establish Communications Request, often abbreviated CR) is sent by whichever side initiates the handshake — it can be sent by either the host or the equipment, unlike many SECS pairs where direction is fixed — and S1F14 (Establish Communications Request Acknowledge, CRA) is the reply confirming the other side is ready to communicate; only after this exchange completes successfully does either side consider the link to be in an online, communicating state.

This handshake is retried, not assumed, which matters in practice because a tool that has just powered on, rebooted, or recovered from a communications fault cannot be trusted to be ready for traffic just because its network link is physically up — S1F13/S1F14 gives both sides an explicit, acknowledged confirmation that the other end is actually ready to process SECS-II messages, not merely reachable. If S1F14 doesn't come back within a timeout, the initiating side retries the S1F13 request rather than assuming failure permanently, which is the standard, expected behavior during equipment startup or after a brief communications interruption — a single missed S1F14 is routine, not necessarily an alarm-worthy event.

S1F13/S1F14 is the session-level prerequisite that every other SECS-II message pair in this catalog depends on — S3F5/S3F6 (Material Found), S6F11/S6F12 (Collection Event Reporting), and every other stream/function pair only have meaning once this handshake has succeeded, which is why it is always the very first exchange in any SECS/GEM communication session, host-initiated or equipment-initiated.