The level of MPC used for an MPC connection is automatically determined by a negotiation between the partner nodes. You can control the level used by coding the MPCLEVEL operand on the TRLE definition statement that defines the MPC connection.

When HPDT MPC is used

If both partner nodes support HPDT MPC, HPDT MPC is automatically used.

VTAM® supports HPDT MPC if it is defined as an HPR APPN node that provides RTP-level HPR support. See High-Performance Routing (HPR) for information about how VTAM is defined as an HPR APPN node that provides RTP-level HPR support.

In Figure 1, assume that both VTAM network nodes are nodes higher than VTAM Version 4 Release 4, each providing RTP-level HPR support. The MPC connection between them, therefore, is an HPDT MPC connection.

When Non-HPDT MPC is used

If either partner node does not support HPDT MPC, non-HPDT MPC is automatically used.

Keep in mind that VTAMs before Version 4 Release 4 do not support HPDT MPC, and therefore, non-HPDT MPC will be used.

In Figure 1, assume that VTAM network node 1 is a VTAM Version 4 Release 4 or higher node that does not provide RTP-level HPR support and that VTAM network node 2 is a VTAM node before Version 4 Release 4. Because VTAM releases before Version 4 Release 4 do not support HPDT MPC, the MPC connection between them is a non-HPDT MPC connection.

Of course, if both nodes are VTAM Version 4 Release 4 or lower network nodes, the MPC connection between them would also be a non-HPDT MPC connection.

Controlling the level of MPC used

Use the MPCLEVEL operand on the TRLE definition statement to control the level of MPC used for the connection. When VTAM and the adjacent node support HPDT MPC, the connection automatically uses HPDT MPC, unless VTAM includes MPCLEVEL=NOHPDT on its TRLE definition statement. When the adjacent node is another VTAM node that supports HPDT MPC, if MPCLEVEL=NOHPDT is coded on the TRLE definition statement of at least one of the VTAM nodes, the connection uses non-HPDT MPC.

Note: There are situations in which you must code MPCLEVEL=NOHPDT. Otherwise, the connection or session requests over the connection will fail. These situations include:

• Both nodes are VTAM Version 4 Release 4 or higher nodes and one of the VTAM nodes does not provide RTP-level HPR support. In this case, MPCLEVEL=NOHPDT must be specified on the TRLE definition statement in the VTAM node that does not provide RTP-level HPR support or the connection attempt will fail. See the following example for a full explanation of this situation.
• Both nodes are VTAM Version 4 Release 4 nodes that provide RTP-level HPR support, but the HPR operand on the PU definition statement in the local SNA major node in a least one of the VTAM nodes is coded as follows:
  • HPR=NO
  • HPR=YES, when the HPR start option specifies HPR=(RTP,NONE) or HPR=(RTP, ANR)
  In these cases, MPCLEVEL=NOHPDT must be specified on the TRLE definition statement in at least one of the VTAM nodes or the connection attempt will fail.

In Figure 1, assume that both VTAM network nodes are VTAM nodes, but that VTAM network node 1 provides RTP-level HPR support and VTAM network node 2 does not. Because the default value for the MPCLEVEL operand is HPDT, during negotiation, both VTAM nodes agree to use an HPDT MPC connection. But, because VTAM network node 2 does not provide RTP-level HPR support, the connection attempt fails. For the connection to be successfully established, it must be a non-HPDT MPC connection. You must code MPCLEVEL=NOHPDT on the TRLE definition statement that defines the connection in VTAM network node 2 to make this a non-HPDT MPC connection, as follows:

Definitions for network node 1 HPR=RTP	Definitions for network node 2 HPR=NONE
TRL Major Node TRLNN1 VBUILD TYPE=TRL MPCLN1 TRLE LNCTL=MPC, MAXBFRU=16, READ=(BCA), WRITE=(BCB) Local SNA Major Node LSNA1 VBUILD TYPE=LOCAL LSNAPU1 PU TRLE=MPCLN1, ISTATUS=ACTIVE, CONNTYPE=APPN, CPCP=YES	TRL Major Node TRLNN2 VBUILD TYPE=TRL MPCLN2 TRLE LNCTL=MPC, MAXBFRU=16, READ=(BCB), WRITE=(BCA), MPCLEVEL=NOHPDT Local SNA Major Node LSNA2 VBUILD TYPE=LOCAL LSNAPU2 PU TRLE=MPCLN2, ISTATUS=ACTIVE, CONNTYPE=APPN, CPCP=YES