Bracket protocol for IMS input

One or more input messages can be received within a bracket.

For example:
  • Any number of nonresponse, nonconversation, noncommand, or nontest mode input messages can be sent within the bracket. The input, the subsequent asynchronous output, or an LUSTATUS can end the bracket. Further, a single nonresponse, nonconversation, noncommand, or nontest mode input message with ATTACH EB can be sent.
  • One response mode or command message, except /TEST, can optionally occur within the same bracket after any of the input messages listed in the previous list bullet. The response mode or command message output ends the bracket.
  • Any number of conversation or test mode inputs followed by conversation or test mode outputs can optionally begin within the same bracket after the input messages listed in the first list bullet. The bracket ends on the last conversation output message (or command complete message from /END for test mode). The bracket can also be ended by the other half session's sending an input LUSTATUS or CHASE with EB, but not by input data sent with EB.
  • The bracket can be ended by an EB occurring on an FMH7 or LUSTATUS resulting from an error.

The following series of tables summarizes the bracket and send/receive indicators acceptable for the various message types input to IMS.

An X in the table indicates that the corresponding entry is supported by IMS.

In the tables the VTAM® indicators are represented by the following abbreviations:
  • BB: Begin-Bracket
  • EB: End-Bracket
  • CD: Change-Direction. Allowed on Last- or Only-in-Chain.
  • BB/EB: Begin- and End-Bracket. Allowed on First- or Only-in-Chain.
Table 1. VTAM bracket and send/receive indicators that are sent with messages to IMS: input message type using ATTACH SCHEDULER
Input message type using ATTACH SCHEDULER BB EB BB/EB BB/CD CD ¬BB, ¬EB, ¬CD
MFS-autopaged input: First page (of multiple page input) X         X
MFS-autopaged input: Nonfirst, nonlast page           X
MFS-autopaged input: Last page: see transaction types            
Nonresponse transaction            
Nonconversational mode transaction Note 1 Note 2 Notes1, 2 Note 1 X X
Response mode (including Fast Path) transaction Note 1     Notes 1, 3 Note 3 X
Conversational transaction Note 1     Notes 1, 3 Note 3 X
IMS message switch X X X X X X
IMS command X Note 4 Note 4 Note 3 Note 3 X
Input while in test mode4         Note 3 X
Notes:
  1. Not valid for the last page of MFS-autopaged input.
  2. Not valid for the first page of MFS-autopaged input.
  3. Denotes the optimal end-of-message indicators to prevent IMS from soliciting change-direction using SNA SIGNAL.
  4. Valid only for /DIS, /RDIS, and /FOR commands. Also optimal for these commands to keep IMS from immediately forcing a between-brackets state by sending LUSTATUS - NO-OP (X'0006') with EB. The output from these commands is always queued and sent asynchronously.
  5. FMH7 messages and LUSTATUS NO-OP indicating EB force end of conversation, response mode, and test mode and cause the associated IMS output message to be dequeued. Further, the Conversational Abnormal Termination exit routine is invoked.
Table 2. VTAM bracket and send/receive indicators that are sent with input messages to IMS using ATTACH (no SCHEDULER)
Input message type using ATTACH (no SCHEDULER) BB EB BB/EB BB/CD CD BB, EB, CD
MFS-autopaged input: First page (of multiple page input) X         X
MFS-autopaged input: Nonfirst, nonlast page           X
MFS-autopaged input: Last page: see transaction types            
Nonresponse, nonconversational mode transaction   X X      
Response mode (including Fast Path) transaction 6 Note 1     Notes 1, 3 Note 3 X
Conversational transaction Note 1     Notes1, 3 Note 3 X

IMS message switch

 X X

ATTACH SYSMSG

 X X
IMS command X Note 4 Note 4 Note 3 Note 3 X
Input while in test mode 5         Note 3 X
Notes:
  1. Not valid for the last page of MFS-autopaged input.
  2. Not valid for the first page of MFS-autopaged input.
  3. Denotes the optimal end-of-message indicators to prevent IMS from soliciting change-direction using SNA SIGNAL.
  4. Valid only for /DIS, /RDIS, and /FOR commands. Also optimal for these commands to keep IMS from immediately forcing a between-brackets state by sending LUSTATUS - NO-OP (X'0006') with EB. The output from these commands is always queued and sent asynchronously.
  5. Applies to test echo mode only. Not applicable to /TEST MFS.
  6. For ISC, response mode operation is forced for attached transactions not indicating EB (regardless of their definition on the TRANSACT macro statement) when the TERMINAL macro statement or ETO user descriptor indicates either TRANRESP or FORCRESP. The input is rejected if the TERMINAL macro statement or ETO user descriptor indicates NORESP.
Table 3. Vtam bracket and send/receive indicators sent with other input messages sent to IMS
Other input message types BB EB BB/EB BB/CD CD BB, EB, CD
VTAM normal flow command/indicator 1, 2 X       X X
FMH7 (ERP) messages   Note 5 X X X  
IMS MFS paging control request (QMODEL FMHs)       X X  
RAP FMH         X  
Notes:
  1. LUSTATUS, CHASE, and CANCEL can indicate EB or CD. Other VTAM normal flow commands or indicators must not indicate either EB or CD.

    When IMS is waiting for conversational input, LUSTATUS and CHASE cannot be sent to IMS unless they also indicate end-bracket. EB causes the conversational output message to be dequeued, the conversation mode to be terminated, and the Conversational Abnormal Termination exit routine to be invoked. The session is terminated if an LUSTATUS or CHASE is received by IMS with any other protocol.

  2. FMH7 messages and LUSTATUS NO-OP indicating EB force end of conversation, response mode, and test mode and cause the associated IMS output message to be dequeued. Further, the Conversational Abnormal Termination exit routine is invoked.