VTAM commands and indicators
VTAM® commands and indicators (communication control information) are necessary for data transmission between an IMS application program and another VTAM logical unit.
The following table shows which VTAM commands and indicators that IMS sends and receives during an IMS session (X=supported). Results are unpredictable if any unsupported commands or indicators are used.
| VTAM command or indicator | IMS sends as Primary half session, Receives as secondary half session | IMS sends as Secondary half session, Receives as primary half session |
|---|---|---|
| Independent of session | ||
| Initiate session | Note 4 | |
| Procedure error | Note 1 | Note 1 |
| Terminate session | Note 5 | |
| Session control commands | ||
| Bind | X | |
| Bind response | X | |
| STSN | X | |
| STSN response | X | |
| Start data traffic (SDT) | X | |
| SDT response | X | |
| Unbind | X | X |
| Normal (synchronous) flow indicators | ||
| Begin bracket (BB) | X | X |
| End bracket (EB) | X | X |
| Change direction (CD) | X | X |
| Commands | ||
| BID | Note 3 | X |
| CANCEL | X | X |
| CHASE | X | X |
| Logical unit status (LUSTATUS) | X | Note 2 |
| Ready to receive (RTR) | X | |
| Bracket initiation stopped (BIS) | X | |
| Expedited (asynchronous) flow commands | ||
| Request shutdown (RSHUT) | X | Note 2 |
| Signal | X | X |
| Stop bracket initiation (SBI) | X | |
Notes:
- Sent by VTAM.
- Not sent by IMS, but optionally sent by the other subsystem and received by IMS when IMS is a primary half session.
- Not sent by IMS, but optionally sent by the other subsystem and received by IMS when IMS is a secondary half session.
- Supported by internal VTAM forms of CINIT (LOGON exit).
- Supported by internal VTAM forms of CTERM (NS and LOSTERM exits).