Handling request headers (RH)

The initial RH is obtained from one of the following places as summarized in Table 1:

RPL flags, if OPTCD=(NUSERRH,NBUFFLST) or OPTCD=(NUSERRH,BUFFLST)
RPL user-RH field, if OPTCD=(USERRH,NBUFFLST)
First buffer-list entry for each buffer group, if OPTCD=(USERRH,BUFFLST).

Table 1. Location of the initial RH
BUFFLST selected	LMPEO selected	USERRH selected	Number of RUs generated	Location of initial RH
no	no	no	1	RPL flags
no	no	yes	1	RPL user-RH field
no	yes	no	1 or more	RPL flags
no	yes	yes	1 or more	RPL user-RH field
yes	no	no	1	RPL flags
yes	no	yes	1	First entry of buffer list
yes	yes	no	1 or more	RPL flags
yes	yes	yes	1 or more	First entry of buffer list associated with each buffer group

The initial RH is used as a model to build the RH for each generated request. The initial RH indicates one of the following: only-in-chain (OIC), first-in-chain (FIC), middle-in-chain (MIC), or last-in-chain (LIC). See Chaining. VTAM® generates requests as shown in Table 2. All generated requests are part of the same chain. If the initial RH specified OIC, a whole chain is generated. If the initial RH specified FIC, MIC, or LIC, a partial chain is generated.

The indicators that VTAM puts into the RH of each generated request depend on the initial RH and on whether the generated request is OIC, FIC, MIC, or LIC. See Figure 1 and Figure 2 for the rules VTAM uses to set the RH of each generated request.

Note: For OPTCD=NLMPEO, the RH propagation rules shown in Figure 1 and Figure 2 do not apply. The initial RH is used for the single request sent.

Table 2. Possible chain indicators resulting from initial RH-chain indicator settings
Initial RH-chain indicators	Resultant RH-chain indicators
OIC	OIC or FIC,LIC or FIC,MIC,…,MIC,LIC
FIC	FIC or FIC,MIC,…,MIC
MIC	MIC,…,MIC
LIC	LIC or MIC,…,MIC,LIC
Note: In this table MIC,…,MIC represents a single MIC request or multiple MIC requests.

In summary, for SEND OPTCD=LMPEO, the input request results in one or more output requests as follows:

All chains are standard SNA chains, requesting no response (RQN), exception response (RQE), or definite response (RQD) as shown in Figure 1 and Figure 2.
POST=SCHED or RESP can be used with SEND OPTCD=LMPEO. The SEND macroinstruction is posted complete when the last request generated from the message has been handled. The POST operand applies to this last request. Thus, posting occurs when the RPL is no longer needed for the request (POST=SCHED) or when the response asked for by the last request has been returned (POST=RESP).
The normal session-level pacing and virtual-route pacing rules apply to requests generated by LMPEO. A large message can take a long time to transmit; therefore, OPTCD=ASY rather than OPTCD=SYN should be used if it is undesirable to suspend the task issuing SEND for that length of time. With OPTCD=ASY, the application program regains control while VTAM is sending the requests generated from the large message.

Additional considerations for posting of SEND are discussed in Exception conditions.

Figure 1. LMPEO handling of selected RH indicators

Initial RH settings RHs generated by LMPEO

-----------------------------------------------------------------
                        FIC + MIC + MIC + . . . + MIC + LIC  OIC
-----------------------------------------------------------------
                        See Notes:
BBI or EBI in:  OIC      2     3     3             3     3    2
                FIC      2     3     3             3     4    4
    (Note 5)    MIC      4     2     3             3     4    4
    (Note 5)    LIC      4     2     3             3    3,7   4
-----------------------------------------------------------------
QRI, CSI or     OIC      2     2     2             2     2    2
EDI in:         FIC      2     2     2             2     4    4
                MIC      4     2     2             2     4    4
                LIC      4     2     2             2     2    4
-----------------------------------------------------------------
FI, RCDI, or    OIC      2     3     3             3     3    2
SDI (Note 6)    FIC      2     3     3             3     4    4
in:             MIC      4     2     3             3     4    4
                LIC      4     2     3             3    3,7   4
-----------------------------------------------------------------
CDI or CEBI in: OIC      3     3     3             3     2    2
    (Note 5)    FIC     3,7    3     3             2     4    4
    (Note 5)    MIC      4     3     3             2     4    4
                LIC      4     3     3             3     4    4
-----------------------------------------------------------------

Legend:

Indicator	Meaning	Indicator	Meaning
BBI	Begin Bracket Indicator	FIC	First-in-Chain
CDI	Change Direction Indicator	LIC	Last-in-Chain
CEBI	Conditional End Bracket Indicator	MIC	Middle-in-Chain
CSI	Code Selection Indicator	OIC	Only-in-Chain
EBI	End Bracket Indicator	QRI	Queued Response Indicator
EDI	Enciphered Data Indicator	RCDI	Request Change Direction Indicator
FI	Format Indicator	SDI	Sense Data Included Indicator

Notes:

Any LMPEO request is rejected with (RTNCD,FDB2)=(X'14',X'7B'), if the pacing indicator (PI), padded data indicator (PDI), or reserved bits (byte 0, bit 3, byte 1, bits 1, 4, or 5) are set.
Output RH has the same setting as the initial RH.
Indicator is set to 0.
Output RH cannot be created from initial RH.
Warning: These lines show what VTAM currently implements if the specified input is given. This input is not valid in SNA, and the VTAM implementation is subject to change. The application program should not specify this input.
Sense Data Included (SDI) requests are not split. FM data exception requests can contain only 4 bytes of data which VTAM gets from the SSENSEO, SSENSMO, and USENSEO fields of the RPL. The SDI indicator is set on the first and only output request.
If no MICs are generated, the output request has the same setting as the input request.

Figure 2. LMPEO handling of selected RH-chain indicators

Initial RH settings RHs generated by LMPEO

-------------------------------------------------------------------------
                     FIC  +  MIC  +  MIC  + . . . +  MIC  +  LIC    OIC
-------------------------------------------------------------------------
RQN (Note 1 ) in:    See Notes:
              OIC    RQN     RQN     RQN             RQN     RQN    RQN 
              FIC    RQN     RQN     RQN             RQN    Note 5 Note 5
              MIC   Note 5   RQN     RQN             RQN    Note 5 Note 5
              LIC   Note 5   RQN     RQN             RQN     RQN   Note 5
-------------------------------------------------------------------------
RQE* (Note 2) in:
              OIC    RQE*    RQE*    RQE*            RQE*    RQE*   RQE*
              FIC    RQE*    RQE*    RQE*            RQE*   Note 5 Note 5
              MIC   Note 5   RQE*    RQE*            RQE*   Note 5 Note 5
              LIC   Note 5   RQE*    RQE*            RQE*    RQE*  Note 5
-------------------------------------------------------------------------
RQD* (Note 3) in:
    (Note 6)  OIC    RQE*    RQE*    RQE*            RQE*    RQD*   RQD*
    (Note 6)  FIC    RQE*    RQE*    RQE*            RQE*   Note 5 Note 5
    (Note 6)  MIC   Note 5   RQE*    RQE*            RQE*   Note 5 Note 5
    (Note 6)  LIC   Note 5   RQE*    RQE*            RQE*    RQD*  Note 5
-------------------------------------------------------------------------
RQX (Note 4) in:
    (Note 6)  OIC    RQN     RQN     RQN             RQN     RQN    RQN
    (Note 6)  FIC    RQN     RQN     RQN             RQN    Note 5 Note 5
    (Note 6)  MIC   Note 5   RQN     RQN             RQN    Note 5 Note 5
    (Note 6)  LIC   Note 5   RQN     RQN             RQN     RQN   Note 5
-------------------------------------------------------------------------

Legend:

*: 1, 2, or 3
RQN: No response requested
RQE: Exception response requested
RQD: Definite response requested
RQX: Invalid combination in SNA

Notes:

RQN = (¬ER,¬DR1,¬DR2) and RESPOND = (NEX,NFME,NRRN)
RQE* = RQE1 or RQE2 or RQE3 where:
- RQE1 = (ER,DR1,¬DR2) and RESPOND = (EX,FME,NRRN)
- RQE2 = (ER,¬DR1,DR2) and RESPOND = (EX,NFME,RRN)
- RQE3 = (ER,DR1,DR2) and RESPOND = (EX,FME,RRN)
RQD* = RQD1 or RQD2 or RQD3 where:
- RQD1 = (¬ER,DR1,¬DR2) and RESPOND = (NEX,FME,NRRN)
- RQE2 = (¬ER,¬DR1,DR2) and RESPOND = (NEX,NFME,RRN)
- RQE3 = (¬ER,DR1,DR2) and RESPOND = (NEX,FME,RRN)
RQX = (ER,¬DR1,¬DR2) and RESPOND = (EX,NFME,NRRN)
The output request cannot be created from input request.
Warning: These lines show what VTAM currently implements if the specified input is given. This input is not valid in SNA and the VTAM implementation is subject to change. The application program should not specify this input.