Message segmentation

We can define IMS transactions as expecting single- or multi-segment input.

The originating IBM MQ application must construct the user input following the MQIIH structure as one or more LLZZ-data segments. All segments of an IMS message must be contained in a single IBM MQ message sent with a single MQPUT.

The maximum length of an LLZZ-data segment is defined by IMS/OTMA (32767 bytes). The total IBM MQ message length is the sum of the LL bytes, plus the length of the MQIIH structure.

All the segments of the reply are contained in a single IBM MQ message.

There is a further restriction on the 32 KB limitation on messages with format MQFMT_IMS_VAR_STRING. When the data in an ASCII-mixed CCSID message is converted to an EBCDIC-mixed CCSID message, a shift-in byte or a shift-out byte is added every time that there is a transition between SBCS and DBCS characters. The 32 KB restriction applies to the maximum size of the message. That is, because the LL field in the message cannot exceed 32 KB, the message must not exceed 32 KB including all shift-in and shift-out characters. The application building the message must allow for this.

Parent topic: How the IMS bridge deals with messages