For switched connections, PU definitions for type 2.1 peripheral nodes can be created dynamically on the VTAM® host accepting the incoming call. For details, see Defining resources dynamically.

If you code PU definition statements for type 2.1 peripheral nodes, consider the following.

• Type 2.1 characteristics

  Type 2.1 peripheral nodes can communicate with each other, and with application programs in VTAM. Communication between type 2.1 peripheral nodes can occur through the main communication path among the subarea nodes in the network. Type 2.1 peripheral nodes support link-level role negotiation, eliminate hierarchical control (no ACTPU or ACTLU unless PU requests), require fewer flows to establish sessions, and use dynamically assigned session identifiers rather than preassigned addresses, all of which require fewer system definitions.

  VTAM performs the directory services function for the subarea network and any APPN end nodes it serves. It locates the other session partner through a type 2.1 logical unit session request. VTAM is also involved in the session setup process when the type 2.1 session request traverses the subarea network, or when it is acting as a network node server for an APPN end node. VTAM or VTAM and NCP together appear and operate as a peer node to any type 2.1 peripheral node that attaches to the subarea network.

• CPNAME operand

  For a type 2.1 peripheral node on a switched or LAN connection, VTAM requires the coding of either the CPNAME operand or both the IDBLK and IDNUM operands on the PU definition statement in a switched major node. You can code all three. During activation of the node, VTAM uses the NETID (if specified) and the control point name (CPNAME) to find the PU and LU definition statements associated with the node. If CPNAME is not in the exchange ID (XID) or if CPNAME is not coded in VTAM, VTAM uses IDBLK and IDNUM instead. (To have VTAM first use IDBLK and IDNUM, use the SWNORDER=STATNID start option or specify the SWNORDER=STATNID operand on the GROUP or LINE definition statement.) VTAM also uses the control point name to locate switched node definitions, even if the boundary function does not provide type 2.1 peripheral node support.

• XID services

  For a type 2.1 peripheral node attached to the communication adapter using an SDLC link, the MODE operand on the LINE definition statement can be used to indicate whether VTAM performs the functions of the primary (PRI) or the secondary (SEC) link station. VTAM uses this PRI or SEC indication to determine its link-level role during the exchange identification (XID) processing for the connection. Because VTAM does not negotiate the primary or secondary role and uses the MODE specification for the XID process, you need to know the link-level role capability of the other type 2.1 connection. For example, if you specify VTAM as primary (MODE=PRI) and the other peripheral node is also primary nonnegotiable, the connection fails.

  If the SDLC line used is a switched link, the XMITDLY operand of the LINE definition statement can be used to specify the amount of time that VTAM should delay before performing XID processing after answering the incoming call. This delay allows the calling peripheral node to initiate XID transmission first and, therefore, to avoid VTAM initiating this process before the type 2.1 peripheral node is ready.

  The XID=YES operand coded on the PU definition statement implies that the contact procedure used is for a type 2.1 peripheral node. VTAM determines whether the peripheral node is a type 2.1 or a type 2 by checking the XID value received from the node either during activation of the node or at CONTACT time for switched nodes.

• XCA local area networks

  Although VTAM can support type 2.1 peripheral nodes that are channel-attached through the external communication adapter (XCA), review the connectivity capabilities of each particular device to ensure it can be channel-attached as a type 2.1 peripheral node.

• Defining a type 2.1 channel
  If you are connecting a channel-attached type 2.1 PU to your host, code a VBUILD definition statement with TYPE=LOCAL specified.

  LSNA3    VBUILD TYPE=LOCAL
  LSNA3PU  PU    CUADDR=051,
                 MAXBFRU=15,
                 PUTYPE=2,
                 SSCPFM=USSSCS,
                 VPACING=0,
                 XID=YES