Appendix D - Recovery after Timeout Flow

Simplify will attempt to transmit a message a parameterized number of times before assuming communications is lost.

Message flow is bi-directional. The POS device or Simplify can initiate a message. In order to avoid timeouts and retransmissions between the POS device and Simplify, each endpoint (POS device or Simplify) should read an incoming message, calculate the LRC, and immediately respond with an ACK or NAK.

message resent after timeout

* Recommended timeout is at least 3 seconds.

Exception to Timeout/Recovery Rules

After a timeout on a non-critical message, Simplify does not expect an ACK and will not retry the message. Sending an ACK for a non-critical message will not cause any issue. The following messages are considered non-critical:

Message Type Exceptions
Status Message
(Tran Type 36-51)
Status Identifier = 001
(For information on Status Identifiers, see Field 11.)

The message flow without an ACK is shown below:

message flow with ACK suppressed