EnquireLink is SMPP command allowing to check communication between ESME and SMSC.
The command can be sent by both client and server.
The EnquireLink mechanism assumes sending special SMPP-request by one of the peers obtaining the proper response. When proper response is received with ESME_ROK status, the connection is considered active. Otherwise, if there is wrong response or no response at all - the connection is to be closed.
To enable periodical connecton check, you need to set the following property:
client.EnquireLinkInterval = TimeSpan.FromSeconds(30);
Read more on page Keeping connection active (InactivityTimeout and EnquireLink)