ENQUIRE_LINK is SMPP command that used to check communication between ESME and SMSC.
To enable this feature you need to set following properties:
_client.NeedEnquireLink = true; _client.EnquireInterval = 60;
NeedEnquireLink property gets or sets a value that indicates whether the EnquireLink should be send. Default is false.
EnquireInterval defines interval in seconds between EnquireLink submitions. Default is 60 seconds.