Some quick examples of what I'm dealing with.  There are about 10error scenarios in all, this is just a couple.

NORMAL COMMUNICATION SCENARIO, MULTIPLE TRANSACTIONS
POS System --------------------------------------------------------------------------------------------FirstData HostDial/Wait for ENQ-----------------------------------------------------------------------------------------------------¢Í ----------------------------------------------------------------------------------------------------------------------ENQSTX/MESSAGE/ETX/LRC-------------------------------------------------------------------------------------------¢Í ---------------------------------------------------------------------------------------------------------------------ACK ------------------------------------------------------------------------------------------STX/MESSAGE/ETX/LRCACK ---------------------------------------------------------------------------------------------------------------------¢ÍSTX/MESSAGE/ETX/LRC-------------------------------------------------------------------------------------------¢Í ---------------------------------------------------------------------------------------------------------------------ACK ------------------------------------------------------------------------------------------STX/MESSAGE/ETX/LRCACK ---------------------------------------------------------------------------------------------------------------------¢Í... additional queued transactions ...STX/MESSAGE/ETX/LRC-------------------------------------------------------------------------------------------¢Í ---------------------------------------------------------------------------------------------------------------------ACK ------------------------------------------------------------------------------------------STX/MESSAGE/ETX/LRCACK ---------------------------------------------------------------------------------------------------------------------¢Í500 Millisecond delayDisconnect-----------------------------------------------------------------------------------------------------Disconnect

Errors Due to Non-verified LRCA transmission in which the host does not calculate the same LRC asreceived from the POS system maybe depicted as follows:POS System First Data HostDial/Wait for ENQ-----------------------------------------------------------------------------------------------------¢Í ----------------------------------------------------------------------------------------------------------------------ENQSTX/MESSAGE/ETX/LRC-------------------------------------------------------------------------------------------¢Í --------------------------------------------------------------------------------------------------------------------NAK*STX/MESSAGE/ETX/LRC-------------------------------------------------------------------------------------------¢Í ---------------------------------------------------------------------------------------------------------------------ACK ------------------------------------------------------------------------------------------STX/MESSAGE/ETX/LRCACK ----------------------------------------------------------------------------------------------------------------------¢ÍDisconnect ---------------------------------------------------------------------------------------------------Disconnect



Timeout ErrorsA transmission in which the POS system sends the message and does notreceive a positive or negativeacknowledgment, but receives another valid control character withinsixty seconds may be depicted asfollows:POS System First Data HostDial/Wait -----------------------------------------------------------------------------------------------------------------¢Í ----------------------------------------------------------------------------------------------------------------------ENQSTX/MESSAGE/ETX/LRC/Wait Up to 60 Seconds--------------------------------------------------------------¢Í --------------------------------------------------------------------------------------------------------------------ENQ*STX/MESSAGE/ETX/LRC (Repeat)--------------------------------------------------------------------------------¢Í ---------------------------------------------------------------------------------------------------------------------ACK ------------------------------------------------------------------------------------------STX/MESSAGE/ETX/LRCACK ----------------------------------------------------------------------------------------------------------------------¢ÍDisconnect ---------------------------------------------------------------------------------------------------Disconnect* If the POS system should receive an ENQ from the host, it shouldre-send the message. Error logic forthis specific scenario can be quite tricky; the ACK preceding the ENQcould easily be seen as theacknowledgment for the request message. Therefore, the POS systemshould recognize an ENQimmediately following as an indication that the First Data host didnot receive the request message, andre-send. Results may vary.