EnquireLink
EnquireLink is a simple, standard PDU used in the Short Message Peer-to-Peer (SMPP) protocol to test connectivity and keep sessions alive between an ESME (External Short Messaging Entity) and an SMSC (Short Message Service Center). It functions as a lightweight heartbeat to verify that the TCP connection and the SMPP session are still operational.
The Enquire Link PDU carries no user data or parameters. It consists of the fixed SMPP PDU
Usage and behavior: Enquire Link is generally sent periodically by either side of the connection to detect
Implementation notes: Enquire Link should not be used for authentication or data transfer; it serves solely