Dependent LU server

The dependent LU server (DLUS) function facilitates conversion from a subarea environment to an APPN environment, allowing you to maintain central management of remote dependent LUs while benefiting from APPN throughout a network.

Note: The DLUR and DLUS architecture supports dependent secondary LUs (SLUs) only. The AS/400® SPLS function is not supported by DLUR and DLUS.

Two LU 6.2 sessions (one inbound, one outbound) are established between a DLUS and a dependent LU requester (DLUR), and these LU 6.2 sessions are collectively known as the CPSVRMGR pipe. SSCP-PU and SSCP-LU session flows use the CPSVRMGR pipe. An SSCP-PU session is established between a VTAM® network node and the PU that owns the dependent LU, and an SSCP-LU session is established between VTAM and the dependent LU. Session initiation flows for the dependent LU are sent over the SSCP-LU session, and VTAM can use subarea or APPN flows to initiate a session with the PLU. BIND and session data are then routed directly between the PLU and the dependent LU.

For example, in Figure 1, VTAMB is a dependent LU server for LU4 and LU5. SSCP-PU sessions are established between VTAMB and PU4 and between VTAMB and PU5, and SSCP-LU sessions are established between VTAMB and the dependent LUs (LU4 and LU5). Session initiation flows for the dependent LUs are sent over the SSCP-LU sessions. VTAMB uses APPN flows to initiate a session with a PLU that VTAM can communicate with through an APPN network (for example, LU2 and LU3), and subarea flows to initiate a session with a PLU reachable through a subarea network (for example, APPLA1). The BIND and session data are then routed directly between the PLU and the dependent LUs.

Figure 1. VTAM functioning as a dependent LU server

To implement the dependent LU server function, consider the following situations:

NODETYPE=NN must be specified for a VTAM DLUS.
For DLUR-initiated PU activation, no system definition is required. The dynamic switched definition facility can be used to dynamically define the PU. If the DLUR is adjacent, a PU name must be added to the REQACTPU by the DLUR. When the DLUR is adjacent, a CPNAME is sent in the REQACTPU and used to search for a PU. The previously defined CPNAME is found, and the REQACTPU is rejected. For information about the dynamic switched definition facility, see Defining resources dynamically and Dynamic switched definitions.
Dynamically defined PUs can be displayed using the DISPLAY ID command, specifying the DLUR CP name on the ID operand. This shows all PUs that currently have an SSCP-PU session (both dynamic and predefined PUs). You can also determine which LUs currently have an SSCP-LU session by displaying a specific PU.
For VTAM to initiate activation of a PU, define the dependent LU requester by including the DLURNAME and DLCADDR operands on the PATH definition statement in the switched major node (regardless of whether its connection to the DLUR is switched or leased). DLURNAME specifies the CP name of the DLUR that owns the PU, and DLCADDR includes data link control (DLC) information used by the DLUR to locate the PU.
In some cases the DLUS and the network node server of the DLUR are different VTAM nodes. In this case, there must be a searchable APPN path from the DLUS to the NNS of the DLUR. This path can go through multiple nodes if necessary.
Note: If the DLURNAME is not fully qualified, the NETID of the DLUS is used.

A sample switched major node to match Figure 1 is shown in Figure 2. DLUR1 is used in the switched major node as the name of the DLUR shown in Figure 1.
The DLUS and DLUR must be connected over an APPN path that supports the CPSVRMGR Class of Service.
Takeover and giveback is supported for DLUR-attached PUs. The PU must be defined in VTAM with ANS=CONT, and the DLUR must be capable of handling ANS=CONT support. Giveback processing for DLUR-supported PUs occurs when an operator command is issued from the DLUS to relinquish control of the PU (for example, V NET,INACT,ID=dlur_pu,G), or an outage occurs for the CPSVRMGR pipe. Takeover processing can occur automatically for redial or can be initiated by the operator with a VARY DIAL command, for PUs previously released by giveback processing.

Figure 2. Switched major node for a dependent LU server

SAMPSWMN VBUILD TYPE=SWNET
PU4      PU    ADDR=01,                                                X
               IDBLK=05D,                                              X
               IDNUM=00001,                                            X
               USSTAB=AUSSTAB,                                         X
               MODETAB=AMODETAB,                                       X
               ISTATUS=ACTIVE                                          X
PATHU4   PATH  PID=1,                                                  X
               DLURNAME=DLUR1,                                         X
               DLCADDR=(1,C,INTPU),                                    X
               DLCADDR=(2,X,05D00001)
LU4      LU    LOCADDR=1,                                              X
               PACING=(1,1),                                           X
               VPACING=2*
PU5      PU    ADDR=02,                                                X
               IDBLK=05D,                                              X
               IDNUM=00002,                                            X
               USSTAB=AUSSTAB,                                         X
               ISTATUS=ACTIVE                                          X
PATHU5   PATH  PID=1,                                                  X
               DLURNAME=DLUR1,                                         X
               DLCADDR=(1,C,INTPU),                                    X
               DLCADDR=(2,X,05D00002)
LU5      LU    LOCADDR=1,                                              X
               PACING=(1,1),                                           X
               VPACING=2,                                              X
               MODETAB=AMODETAB

Notes:

If using NCP, NCP Version 6 Release 2 or later is required.
The VARY INACT,TYPE=GIVEBACK command is used to release a DLUR-attached switched PU (and its subordinate LUs) from SSCP ownership. To use this function, the DLUR must support ANS=CONT.
A DLUS can serve multiple DLURs simultaneously.
A DLUR can be served by multiple DLUS VTAMs simultaneously.
Multiple DLURs can support the same PU (one at a time). The SSCP-PU session is through only one DLUR at any given time.
DLUS function cannot be used with XRF or cryptography in an XRF environment.
Redial occurs as follows for DLUS supported PUs:
- When a DLUS initiates the activation of a PU but receives a negative response, VTAM attempts to redial over each valid path statement for the PU until successful or until all valid paths have been tried. Redial does not occur if the negative response indicates that the PU is already active, or that the fully-qualified PCID is not unique. If the fully-qualified PCID is not unique, the DLUS attempts to redial the PU over the same path with a newly generated PCID.
- Redial does not occur if PU activation was initiated by the DLUR.
- When a protocol violation, TDU error, or CPSVRMGR session outage signal is received for a particular DLUR, VTAM attempts to redial every active or pending-active PU served by that DLUR for which a valid PATH statement is found. If the PU is already active, VTAM performs the following actions:
  - If the PU was defined with ANS=CONT and the DLUR supports this function, giveback processing is performed before attempting redial.
  - If the PU was defined with ANS=STOP or the DLUR does not support ANS=CONT, the PU is deactivated before attempting redial.
When a CP-CP session between a DLUS and DLUR fails, the CPSVRMGR session is deactivated, enabling reactivation of the CP-CP session.
If the DLUS is located in a different APPN subnetwork from that of the DLUR or the PLU, APPN multiple network connectivity support is required (see Dependent LU server support across subnetwork boundaries). If CPSVRMGR pipe initiation is attempted across an APPN subnetwork boundary and the DLUR does not support this function, a protocol violation is detected and the pipe is terminated.
Information regarding DLUR-attached resources can be processed by the configuration services XID exit. This exit routine can be coded so that VTAM either processes or denies requests for contact from known switched devices, or so that VTAM processes or denies requests for PU activation from a DLUR. For details, seez/OS Communications Server: SNA Customization.
The IDBLK/IDNUM specified on the PU definition statement must match the value specified on the DLCADDR operand (when DLCADDR information is provided for IDBLK/IDNUM) on the associated PATH statement.
When a DLUR-attached dependent LU starts a session, or reports an active session as part of DLUR takeover, VTAM (as the DLUS) receives session information about the SESSST and passes that information to the network logical data manager (NLDM). However, if the session uses HPR and a path switch occurs, VTAM will not be aware of the change unless VTAM is at one end of the HPR route or if DLURSAW=YES is used. To supply NLDM with the updated path switch data between the DLUR and the other end of the session, even when VTAM is not at one end of the HPR route, use the DLURSAW=YES (this is the default) start option. The DLUR must be capable of reporting this information and be configured to do so.
For information about the interaction between the DLURSAW and SAVERSCV start options, see the z/OS Communications Server: SNA Resource Definition Reference.