Output format control for ISC (DPM-Bn) subsystems

Format control

For ISC nodes, MFS allows several specifications to control the format of output messages. If OPTIONS=DPAGE or OPTIONS=PPAGE is specified on the DIV statement, MFS sends an output message in multiple logical or presentation pages. Transmission of these pages within the message occurs on demand or automatically when you set byte 1 bit 5 of the system control area (SCA).

Function management (FM) headers

FM headers are headers on output messages that control functions such as paging.

Paged output messages

For DPM-Bn paging support, if OPTIONS=DPAGE or OPTIONS=PPAGE is specified on the DIV statement, MFS sends an output message in multiple logical or presentation pages.

Demand paging

With demand paging, the logical or presentation pages are sent only when a paging request is received from the other subsystem. The initial output for the message contains only the ATTACH FM header. If DIV OPTIONS=DNM is specified, the data structure name (DSN) is also transmitted.

Autopaged output

This option is available message-by-message, based on SCA values. With this facility, the logical or presentation pages are sent immediately, in multiple transmission chains (one transmission chain per page). With this option, the receiver obtains an entire output message in multiple transmission chains. Each transmission chain contains the DSN, if required.

If no data exists for variable-length fields of a page within the message, a null data chain can result.

Byte 1 bit 5 in the DSCA= operand of the DEV statement or in the SCA option of the MFLD statement indicates autopaged output.

If PAGE=YES is specified in the corresponding MSG definition and autopaged output is requested, the PAGE=YES specification (operator logical paging) function is reset and the output message is dequeued at the end of the message. Operator logical paging applies only to MFS demand paged output.

Output modes

For output from IMS, the ATTACH manager provides for two blocking algorithms: variable length, variable blocked (VLVB) records and chained Request/Response Unit (RUs, MFS stream mode). Each record presented by MFS to the ATTACH manager is preceded by a length field when sent to the other subsystem. The length field contains the size of the record presented by MFS. The record itself is sent in as many RUs as required. Fields span RU boundaries but do not span record boundaries. The number of VLVB records in the transmission chain and the maximum size of the MFS record depend on the output mode selected and the paging option specified.

In stream mode, the way DFLDs are defined depends on the OPTIONS= keyword used:

• For OPTIONS=MSG (paging is not defined), DFLDs are defined in a DPAGE.
• For OPTIONS=DPAGE (paging is defined), DFLDs are defined in a DPAGE.
• For OPTIONS=PPAGE (paging is defined), DFLDs are defined in a PPAGE.

For all three OPTIONS= keyword settings, All the DFLDs defined in a DPAGE (or PPAGE) are grouped into a single MFS record for transmission, and all the data in one DPAGE (or PPAGE) is equal to one MFS record and equal to one output RU chain. One or more RUs are sent in the single transmission chain of the output message.

If the OFTAB parameter of a DIV or DPAGE statement is defined, contiguous output field tab separator characters are removed and are not sent to the subsystem in the following cases:

• At end of message for OPTIONS=MSG
• At end of DPAGE for OPTIONS=DPAGE
• At end of PPAGE for OPTIONS=PPAGE

In record mode, the DFLDs defined in a DPAGE or PPAGE are grouped into smaller records for transmission. The RCDCTL parameter of the DIV statement is used to define the maximum length of the MFS record created. If the RCDCTL= parameter is not specified, the default value allows for records of up to 256 bytes in length. The RCD statement is used to start a DFLD on a new record boundary.

If the OFTAB parameter is defined, contiguous output field tab separator characters at the end of the record (for omitted fields and possible short last data field) are removed before transmission. If the entire record is thus eliminated and additional data records follow, a 1-byte record containing the single output field tab separator character is sent. The record is eliminated in the following cases:

• At end of message for OPTIONS=MSG
• At end of DPAGE for OPTIONS=DPAGE
• At end of PPAGE for OPTIONS=PPAGE

One or more VLVB records are sent in a single transmission chain of the output message (OPTIONS=MSG) or the page (OPTIONS=DPAGE or PPAGE).