If a request arrives from the other end of the session for which VTAM® detects an error (for example, the request arrived with a sequence number that was not one greater than the previous sequence number), VTAM puts X'04' in register 0, X'04' in the recovery action return code field (RTNCD) of the RPL, and X'03' in the specific error return code field (FDB2) of the RPL. It also puts values in the SSENSEI, SSENSMI, and USENSEI fields of the RPL. Unless the other end of the session does not want a response (the RESPOND field contains NFME,NRRN), the VTAM application program, either in the SYNAD exit routine or perhaps later in some other part of the program, must send a response. An exception to this rule is this: if a chain of requests is being received, and a negative response has been returned to a request that was received as part of the chain, and remaining requests of the chain are being received as exception requests, only the first negative response should be sent and the remaining requests should be disregarded.

Before sending the negative response, the values in the SSENSEI, SSENSMI, and USENSEI fields must be transferred to the SSENSEO, SSENSMO, and USENSEO fields of the RPL used to send the response.

Sense codes are discussed in System-sense information.