gtps2m2wACF/SNA Data Communications Reference

VTAM Considerations

This section describes considerations for VTAM.

Class of Service, Virtual Routes, and Transmission Priority

The capability exists in an SNA 4.2 level network to have three transmission priority levels (0, 1, and 2) and the traffic flowing in the network will be assigned 1 of the levels. TPF only supports high priority (2) for sessions across an SNI NCP. For SNA CTC, TPF only supports medium priority (1). This is because priority 2 traffic is not queued by VTAM, but is sent immediately.

TPF does not provide a class of service (COS) table; however, for TPF/APPC parallel sessions you can specify user-defined COS name with the PARACOS parameter on the SNAKEY macro. (See the TPF ACF/SNA Network Generation for more information on the SNAKEY macro.)

For communications with VTAM for a gateway NCP, it is recommended that a COS table contain VR0, TP2 as the first virtual route in any COS entries used where VTAM will be the primary side of a session with TPF (for example, CDRM). Otherwise, when activating sessions, VTAM will needlessly attempt to activate virtual routes that TPF will reject. TPF only supports 1 VR (VR0, TP2) and TPF has to be the primary side of the virtual route.

For SNA CTC, the COS name specified by VTAM must contain the following routes:

When VTAM requests a session for which it is the primary side (for example, ACTCDRM, CICS to SLU-P), VTAM chooses the VR. Because TPF only supports these routes, it is recommended that the ISTVTCOS and default COS table entries have the NCP or SNA CTC virtual routes as the first entry in the VR list.

On request for a session, TPF only selects the routes defined. Immediately after the XID exchange, TPF attempts to activate ERs and VRs. TPF responds negatively to any attempt by VTAM or another TPF to activate a VR that does not request VR0 on TG1 or VR1 on TG2 because other VRs are not defined to TPF.

TPF requires that the virtual route use pacing windows with equal minimum and maximum values; there is no adaptive VR pacing. TPF enforces these restrictions on path definition:

It is recommended that TPF be the primary side of the virtual route to set pacing windows. If VTAM is allowed to be the primary side of the virtual route, the VRPSW01 in the PATH statement for the TPF subarea must set the minimum and maximum window size to be of equal values. This is because TPF does not support adaptive VR pacing.

See VTAM Network Implementation Guide and NCP/SSP/EP Resource Definition Reference for more information about transmission priorities and virtual routes.

Other VTAM Considerations

When TPF is PU type 5 node:

For CTC, with the definition of MAXBFRU, TPF accepts a dynamic buffer size from VTAM at XID time subject to available buffers from the pool. When coding the DELAY operand on the VTAM side, you should be aware that the TPF value is determined by the SNAPOLL parameter of the SNAKEY macro. This SNA polling time interval can be from 10 milliseconds to 50 milliseconds.

VTAM Considerations for NCP 5.3

In the CDRM deck for TPF for NCP Version 5 Release 3 or higher, all GWPATH statements should be coded with the ADJNETEL parameter omitted. This causes VTAM to use the default value of 1 for the CDRM representing TPF. If any 37X5 with NCP 5.3 or higher is channel-attached to TPF, ADJNETEL=1 is required.