Recoverable messages

To ensure that a recoverable transaction can be recovered, IMS requires the following response protocols for each recoverable message sent or received.

  • Messages that are not MFS-paged messages:

    An exception DR2 (RQE2) must be requested on each nonlast (or when it is not the only) RU of an SNA chain.

    Except when change-direction is sent, each last or only RU of an SNA chain must request a DR2 (RQD2). Either exception DR2 (RQE2) or RQD2 can be requested when change-direction is sent.

    A sync-point response on the last or only RU of an SNA chain always indicates end-of-message. End-of-message always occurs at end-of-chain for single chain (non-MFS-paged) messages.

  • First chain of asynchronous (ATTACH SCHEDULER) demand-paged message:

    The first chain (OIC) of asynchronous demand-paged messages is an ATTACH for the SCHEDULER model. This OIC requests a DR2 (RQD2) with end-bracket. This allows the application to be asynchronously scheduled to receive the message and leaves the session in a state to be allocated to the scheduled application.

  • Nonlast pages of MFS demand-paged (output using ATTACH or ATTACH SCHEDULER) messages, and last pages of MFS-operator logical-paged (OLP) output:

    An exception DR1 (RQE1) is requested on each nonlast (or when it is not the only) RU of an SNA chain (MFS demand-page).

    Each last or only RU of an SNA chain (MFS demand-page) requests exception DR1 (RQE1) with change-direction.

  • Last pages of MFS demand-paged (output) messages:

    An exception DR2 (RQE2) is requested on each nonlast (or when it is not the only) RU of an SNA chain (MFS demand-page).

    Except when change-direction is sent on the last page, each last or only RU of an SNA chain (MFS demand-page) requests a DR2 (RQD2). Exception DR2 (RQE2) with change-direction is requested.

    A sync-point response on the last or only RU of an SNA chain always indicates end-of-message. A sync point must always be requested on the last page of MFS demand-paged messages to ensure end-of-message.

  • First, nonlast pages of MFS-autopaged messages:

    An exception DR1 (RQE1) is requested on each nonlast (or when it is not the only) RU of an SNA chain (MFS autopage) sent to IMS and must be requested on each nonlast (or when it is not the only) RU of an SNA chain (MFS autopage) received by IMS.

    RQD1 is requested on the last or only RU of the first SNA chain of an MFS-autopaged output message sent by IMS.

    RQD1 must be requested on the last or only RU of the first SNA chain of an MFS-autopaged input message received by IMS when the other half session is initialized as the primary half session (bidder). Either exception DR1 (RQE1) or DR1 (RQD1) can be requested on the last or only RU of this SNA chain when the other half session is initialized as the secondary half session (first speaker). Change-direction is not sent and must not be requested on nonlast pages of MFS-autopaged input and output messages.

  • Nonfirst, nonlast pages of MFS-autopaged messages:

    An exception DR1 (RQE1) is requested on each RU (including last or only) of an SNA chain (MFS autopage) sent by IMS. An exception DR1 (RQE1) must be requested on each nonlast (or when it is not the only) RU of an SNA chain received by IMS. Either exception DR1 (RQE1) or RQD1 can be requested on each last or only RU of an SNA chain received by IMS. Change-direction is not sent and must not be requested on nonlast pages of MFS-autopaged input and output.

  • Last pages of MFS autopaged messages:

    An exception DR2 (RQE2) is requested on each nonlast RU of an SNA chain (MFS autopage) sent by IMS and must be requested on each nonlast RU of an SNA chain (MFS autopage) received by IMS.

    Except when change-direction is sent on the last page, each last or only RU of an SNA chain (MFS autopage) requests a DR2 (RQD2). Exception DR2 (RQE2) is requested when change-direction is sent.

    Except when change-direction is received on the last page, each last or only RU of an SNA chain of an MFS-autopaged input must request a DR2 (RQD2). Either exception DR2 (RQE2) or definite response 2 (RQD2) can be requested when change-direction is indicated.

    A sync-point response on the last or only RU of an SNA chain or on an LUSTATUS - commit always indicates end-of-message. A sync point must always be requested on the last page or on an LUSTATUS - commit following the last page of autopaged messages to ensure end-of-message.

For the case when allowing RQE1 on the last or only RU of an SNA chain that does not indicate a change-direction for MFS-autopaged input or output, an exception to the preceding protocols occurs when the session bind indicates DEFINITE RESPONSE CHAINS. If the definite response chains parameter is set for the IMS half session, each last or only RU defined that does not also indicate change-direction is sent requesting RQD1 or RQD2. RQD1 or RQD2 must be requested by the other half session under these same conditions if its session bind indicates DEFINITE RESPONSE CHAINS. Both exception and definite response (DR1 and DR2) are valid if change-direction is indicated under definite response chain rules.