You can use MPC connections in an APPN network to connect VTAM® to adjacent APPN nodes and to connect VTAM to a port on the IBM® Open Systems Adapter that provides native access to an ATM network.

How VTAM uses HPDT MPC connections in an APPN network

HPDT MPC is used by VTAM in an APPN network to enable the following connections:

• APPN node-to-node connections (ANNCs)

  ANNC connections can be between a VTAM APPN host node and an adjacent VTAM APPN host node or between a VTAM APPN host node and an adjacent nonhost APPN node.

  Connections between two VTAM APPN host nodes in a sysplex can also use the cross-system coupling facility (XCF). See Dynamic definition of VTAM-to-VTAM connections for more information.

• ATM Native connections

  HPDT MPC enables a connection between a VTAM APPN host node and an IBM Open Systems Adapter port that provides native access to an ATM network. See ATM native connections for more information.

How VTAM uses non-HPDT MPC connections in an APPN network

Non-HPDT MPC is used by VTAM to enable connections only between a VTAM APPN host node and an adjacent VTAM APPN host node. These connections are called APPN host-to-host channel (AHHC) connections. AHHC connections can be considered synonymous with non-HPDT MPC connections.

Steps involved in using HPDT and non-HPDT MPC connections in an APPN network

To use an MPC connection in an APPN network, you must complete the following steps:

1. Define the MPC connection.
2. Define the partner node.
3. Activate the resources that enable the MPC connection.

Note: If VTAM is using the functions of XCF in a sysplex, these steps can be performed dynamically. See Dynamic definition of VTAM-to-VTAM connections for more information.

Defining an MPC connection:

You define an MPC connection in the transport resource list (TRL) major node. The characteristics of the connection are defined on a TRLE definition statement. You must code a TRLE definition statement for each MPC connection.

Defining the partner node:

As explained earlier, VTAM uses an MPC connection to connect to:

• An adjacent APPN node

  You define an adjacent APPN node (host or nonhost) in the local SNA major node. The TRLE operand on the PU definition statement in the local SNA major node specifies the name of the TRLE definition statement in the TRL major node. The TRL major node defines the MPC connection to be used between VTAM and the adjacent APPN node.

  For TCP/IP to use an MPC connection, the device name on the DEVICE statement must match either the MPC TRLE name (for MPCPTP devices) or the TRLE PORTNAME (for MPCIPA or ATM devices). TCP/IP cannot use MPC connections with an MPCLEVEL of NOHPDT. For more information, see the z/OS Communications Server: IP Configuration Guide and the z/OS Communications Server: IP Configuration Reference.

• A port on an IBM Open Systems Adapter that provides native access to an ATM network

  You define a port on an IBM Open Systems Adapter in the external communications adapter (XCA) major node. For information about how to define an IBM Open Systems Adapter port and how to specify the MPC connection to be used between VTAM and the port, see Defining ATM native connections to VTAM.

Activating the resources that enable the MPC connection:

After creating the TRL major node and the major node that defines the partner node (local SNA or XCA), you can use the MPC connection by activating the appropriate resources. For an MPC connection between VTAM and an adjacent APPN node, follow the steps below:

1. Activate the TRL major node.
2. Activate the local SNA major node.
3. Activate the PU that defines the connection to the adjacent node as an APPN PU.

For an MPC connection between VTAM and a port on an IBM Open Systems Adapter, see ATM native connections for information about how to activate the appropriate resources.

Multiple TRL major nodes are allowed to exist in VTAM, and each can be dynamically modified using V NET,ACT,ID= with the UPDATE operand.

If UPDATE=ALL is specified, the VTAMLST member designated with the ID operand replaces the existing TRL major node. However, note that TRLEs in use are not deleted and remain in the TRL major node along with the new TRLEs.

Note: When there is only one active TRL major node, UPDATE=ALL deletes or replaces all inactive TRLEs. When there are multiple active TRL major nodes, UPDATE=ALL deletes or replaces only the inactive TRLEs that exist in the TRL major node being activated. If an inactive TRLE is defined in another TRL major node, it will not be deleted and a name conflict will result if an attempt is made to replace it later.

If UPDATE=ADD is specified, the TRLE entries in the VTAMLST member identified on the ID operand are added to the TRL major node if they do not already exist in any TRL major node.