An SMPP keep-alive command exchanged periodically between an ESME and SMSC to verify that the connection is still active.
Why enquire_link Matters
An idle SMPP connection can sit for minutes without either side sending anything, and firewalls, load balancers, or NAT devices in between will often drop a TCP connection that looks inactive, without telling either endpoint. enquire_link exists so a dead connection gets detected in seconds rather than only surfacing the next time a real message fails to send.
How enquire_link Works
Either side, though typically the ESME, sends an enquire_link PDU on a fixed interval, commonly every 10 to 60 seconds. The other side must respond with enquire_link_resp; if no response arrives within a configured timeout, the session is treated as dead and the client re-binds.
How SMPPCenter Uses This
SMPPCenter's SMPP server sends and expects enquire_link on every idle bind, so a dropped connection is detected and cleared within seconds instead of waiting on a much slower TCP-level timeout.
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API integration was straightforward and the support team assisted us throughout deployment. We now manage multiple operator connections from a single platform.
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