Request unit (RU)

The Request Unit is the information that is being sent between the two network addressable units (NAU) on the session.

Depending on the session the RU can take different forms.

SSCP sessions:

  • The first bytes of the RU indicate a request or response code. Depending on the code, the rest of the RU takes a format specific for that code. For example, a CDINIT (Cross Domain INITiate) has a code of X'818641' while a SESSST (session started) RU has X'810686' as the first 3 bytes of the RU.

LU to LU sessions:

  • The first byte might contain a code like the code in the SSCP sessions. The BIND has a code of X'31' and has a standard format.

The first bytes of the RU might be a Function Management Header (FMH). The distributed data facility (DDF) uses FMH5 to start conversations and for CNOS. It also uses FMH7 for errors. Usually, the FMH is followed by other data that is being sent.

The request unit (RU) can be data only, in a format (or it might be unformatted) that is recognized only by the applications on the session.

Figure 1. Outbound VTAM buffer entry
   USRFD FEF ASCB 00F9D980            JOBN DBD2DIST
              BUFF    LUDBD1  /LUDBD2      LRC(000,000)    OUTBOUND
              VTAM    TH=40000000 00000000 0000000E 0000000F 1C00006B 006E0007 0350  RH=0B90A0
                                              270502FF 0003D000 400430F0 F3F20000 00000000  *........ ..032......*
                                              00000000 00000000 00000000 00000000 00000003  *....................*
                                              26EFFE41 550010D4 C2C84000 00032641 080060D4  *.......MBH .......-M*
                                              C9C24000 00008B00 00000000 00000000 010002A0  *IB .................*
                                              EFCF1437 699C01A0 EFCF1437 699C0100 00000000  *....................*
                                              00000000 00000000 00000000 00000000 00000000  *....................*
                                              00000000 00000000 00000000 00000000 00000000  *....................*
                                              00000000 00000000 000000C9 D4E2D5C5 E34040D3  *...........IMSNET  L*
                                              E4C4C2C4 F24040A0 EFCF1437 91008000 0000E2E3  *UDBD2  .....j.....ST*
                                              E4E3E3C7 C1D9E36D D7D9D6C4 404041             *UTTGART_PROD  .     *
             TIME    48910.013156