Layout of the DEFINE/DISPLAY control block

Table 1 shows the layout of the DEFINE/DISPLAY session limits control block. The field descriptions of the DEFINE/DISPLAY session limits control block follow the layout.

Table 1. Layout of the DEFINE/DISPLAY session limits control block
Byte (Hex) Bit Symbolic Name DSECT Name Usage
0 0–1 SESSCAP2. SLDSCAP Session capability of partner LU
0 2–3 SYNCLVL2 SLDSYNCH Negotiated synchronization level
0 4–7 (reserved)    
1 0 CONVSECV2 SLDCLSV Whether security information is valid
1 1 CONVSECP2 SLDPCLSA Whether the partner LU accepts security access subfields
1 2 ALRDYVP2 SLDPAVFA Whether the partner LU accepts the already-verified indicator
1 3 PRSISTVP2 SLDPPV Whether the partner LU accepts the persistent-verification indicator
1 4 CONVSECL1 SLDLCLSA Whether the local LU accepts security access subfields
1 5 ALRDYVL1 SLDLAVFA Whether the local LU accepts the already-verified indicator
1 6 PRSISTVL1 SLDLPV Whether the local LU accepts the persistent-verification indicator
7 (reserved)      
2 — FQNLEN2 SLDFQNLN Length of partner LU's fully-qualified name
3–13 — FQNAME2 SLDFQNAM Partner LU's fully-qualified name
14 0—1 CONVCAP2 SLDCNVCP Negotiated conversation capability of partner LU
14 2—7 (reserved)    
15 — NAMEUSE2 SLDNMUSE Form of name being used by the local LU on sessions with the partner LU
16 — NMTYPE2 SLDTYPE Type of LU entry in the LU-mode table
17–27 — (reserved)    
28–29 — DSESLIM1 SLDDSESL The value of the maximum session limit for the mode name. This value is used when the application program is the target side of a CNOS request.
2A–2B — DMINWNL1 SLDDMCWL The number of parallel sessions of which the application program is the contention winner. This value is used when the application program is the target side of a CNOS request.
2C–2D — DMINWNR1 SLDDMCWP The number of parallel sessions of which the partner LU is the contention winner. This value is used when the application program is the target side of a CNOS request.
2E 0 DRESPL1 SLDDRSPL Whether the LU is willing to be responsible for session deactivations. This value is used when the application program is the target side of a CNOS request.
2E 1 DDRAINL1 SLDDDRAL Whether the LU accepts permission to drain its allocation requests. This value is used when the application program is the target side of a CNOS request.
2E 2 DELETE1 SLDDELET Whether a mode name entry can be deleted from the LU-mode table
2E 3 AUTOSET3 SLDAUTOS Whether the AUTOSES field can override the number of contention-winner sessions started automatically
2E 4 DELUNUSE SLDDNUNS Whether unusable logmode entries are being deleted on a MODIFY DEFINE command
2E 5–7 (reserved)    
2F 0 DRAINL2 SLDDRAL Whether the application program can drain its allocation requests
2F 1 DRAINR2 SLDDRAP Whether the partner LU can drain its allocation requests
2F 2–7 (reserved)    
30–31 — SESSLIM2 SLDSESSL Returns the session limit for the current logon mode name group
32–33 — MINWINL2 SLDMCWL Returns the current number of parallel sessions of which the application program is to be the contention winner
34–35 — MINWINR2 SLDMCWP Returns the current number of parallel sessions of which the partner LU is to be the contention winner
36–37 — AUTOSES1 SLDAUTO Specifies or returns the number of contention-winner sessions that VTAM® starts automatically for the local LU after the CNOS negotiation
38–39 — SESSCNT2 SLDSESSC Returns the number of active mode name group sessions
3A–3B — WINLCNT2 SLDWINLC Returns the number of currently active sessions in which the application program is the contention winner
3C–3D — WINRCNT2 SLDWINPC Returns the number of currently active sessions in which the partner LU is the contention winner
3E–3F — FREECNT2 SLDFREEC Returns the number of free, active sessions
40–41 — QALLOC2 SLDQALLC Returns the number of queued ALLOCATE requests
42–43 — (reserved)    

The following notes apply to the entries in the Symbolic Name field.

1   This field specifies input for the DEFINE command and returns output for the DEFINE and DISPLAY commands.

2   This field returns only output.

3   This field specifies only input.

In the following description of the control block, the symbolic name of the field is given, followed by the actual DSECT label in parentheses.
  • ALRDYVL (SLDLAVFA) indicates that the local LU accepts the already-verified indicator on conversation requests.
    • B'0' (NO) specifies that the local LU does not accept already-verified requests.
    • B'1' (YES) specifies that the local LU does accept already-verified requests.
  • ALRDYVP (SLDPAVFA) indicates that the partner LU accepts the already-verified indicator on conversation requests.
    • B'0' (NO) specifies that the partner LU does not accept already-verified requests.
    • B'1' (YES) specifies that the partner LU does accept already-verified requests.
  • AUTOSES (SLDAUTO) returns the value specified by the application program for the number of contention-winner sessions that the application program requests VTAM to activate automatically.
  • AUTOSET (SLDAUTOS) specifies whether the content of the AUTOSES field is to be used to override the default values provided by the APPL definition statement. If a value is provided but the bit is not set, VTAM uses the default values from the APPL definition statement.
  • CONVCAP (SLDCNVCP) indicates the negotiated conversation capability of the partner LU.
    • B'10' (FULL-DUPLEX) indicates that sessions with the partner LU are capable of full-duplex or half-duplex conversations and expedited data is allowed.
    • B'01' (HALF-DUPLEX) indicates that sessions with partner LU are capable of half-duplex conversations only.
    • B'00' (UNKNOWN) indicates that the conversation capability of the partner LU is unknown.
  • CONVSECL (SLDLCLSA) indicates whether the application program accepts FMH-5s that include access security subfields.
    • B'0' (NO) indicates that the application program does not accept security information when receiving allocation requests.
    • B'1' (YES) indicates that the application program does accept security subfields on an FMH-5.
  • CONVSECP (SLDPCLSA) indicates whether the partner LU accepts FMH-5s that include access security subfields.
    • B'0' (NO) indicates that the partner LU does not accept security information when receiving allocation requests.
    • B'1' (YES) indicates that the partner LU does accept security subfields on an FMH-5.
  • CONVSECV (SLDCLSV) indicates whether the returned security information in the control block is valid. VTAM does not set the security information until the first session is established with a partner LU.
    • B'0' (NO) indicates that a session has not been established with the partner LU; therefore, the security information in the control block cannot be used.
    • B'1' (YES) indicates that a session has been established and that the security information in the control block can be used.
  • DELUNUSE (SLDDNUNS) indicates that the MODIFY DEFINE command is being used to delete LU-mode table entries that are marked UNUSABLE. For more information about the types of LU-mode table entries, see LU entries in the LU-mode table. For more information about using the MODIFY DEFINE command, refer to z/OS Communications Server: SNA Operation.
  • DDRAINL (SLDDDRAL) specifies whether VTAM should accept permission on a CNOS request, on behalf of the local LU, to drain the local LU's allocation requests. This field applies to the local LU when it is the target. (The local LU can be either the source or the target.) This field applies only if the session limit is being reset to 0.
    • B'1' (ALLOW) specifies that VTAM accepts a CNOS request specifying the LU can drain its allocation requests. If DDRAINL=ALLOW is specified, VTAM performs no negotiation of the drain-target value carried in the received CNOS request.
    • B'0' (NALLOW) specifies that VTAM does not accept a CNOS request specifying the LU can drain its allocation requests. If DDRAINL=NALLOW is specified, VTAM negotiates the drain-target value to indicate no draining is to be performed.

    For single-session connections, this field is not applicable.

    Note: If a CNOS request for all mode names is received, the DDRAINL parameter is used to set the DRAINL value for each mode name associated with the LU. The DDRAINL value has to be set for each mode name.
  • DELETE (SLDDELET) indicates whether a mode name entry can be considered for deletion from the LU-mode table. This field applies only if the session limit is being reset to 0.
    • B'1' (ALLOW) specifies that a mode name entry can be considered for deletion from the LU-mode table.
    • B'0' (NALLOW) specifies that a mode name entry will not be considered for deletion from the LU-mode table.
    Note: Deletion saves storage because subsequent CNOS requests, if any, use the values in the APPL definition statement.
  • DMINWNL (SLDDMCWL) contains the number of parallel sessions of which the application program is guaranteed to be the contention winner. This value is used when the LU is the target side of the negotiation and also when the LU is the source side but did not specify session negotiation limits on the APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS macroinstruction. (When an LU sends a CNOS request to the local LU, the local LU becomes the target .) The specified number can range from 0–32767.

    For single-session connections, this field is not applicable.

  • DMINWNR (SLDDMCWP) contains the number of parallel sessions of which the partner LU is guaranteed to be the contention winner. This value is used for CNOS negotiation. The specified number can range from 0–32767. This value is used when the LU is the target side of the negotiation and also when the LU is the source side but did not specify session negotiation limits on the APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS macroinstruction.

    For single-session connections, this field is not applicable.

  • DRAINL (SLDDRAL) indicates whether the application program currently enables draining of allocation requests. This field applies only if the session limit is 0. This field also is not applicable to the SNASVCMG sessions. This is not the defined drain-local parameter, as provided on the APPL definition statement or the APPCCMD CONTROL=OPRCNTL, QUALIFY=DEFINE macroinstruction. It is the actual drain-local parameter supplied through the APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS macroinstruction or agreed upon during a CNOS negotiation. (The defined drain-local parameter is returned to the application program through the DDRAINL field described in this section.)
    • B'0' (NO) specifies that the LU cannot drain its allocation requests. All requests currently awaiting allocation, or subsequently issued, at the LU are rejected with a return code indicating the session limit is 0.
    • B'1' (YES) specifies that the LU can drain its allocation requests. The LU continues to allocate conversations to the sessions until no requests are awaiting allocation, at which time its draining is ended. Allocation requests that are issued at the LU while draining is taking place are added to the LU's queue of allocation requests to be serviced. All allocation requests issued at the LU after draining is ended are rejected with a return code indicating the session limit is 0.
  • DRAINR (SLDDRAP) indicates whether the partner LU can drain its allocation requests. This field applies only if the limit is 0.
    • B'0' (NO) specifies that the partner LU cannot drain its allocation requests. All requests currently awaiting allocation or subsequently issued at the partner LU are rejected with a return code indicating the session limit is 0. For parallel-session connections, the partner LU cannot negotiate this field.
    • B'1' (YES) specifies that the partner LU can drain its allocation requests. The partner LU continues to allocate conversations to the sessions until no requests are awaiting allocation, at which time its draining is ended. All allocation requests issued at the partner LU after draining is ended are rejected with a return code indicating the session limit is 0.
    Note: Because of the method of negotiating a CNOS request for all mode names, the value of the DRAINR parameter cannot be the same as the value of the partner LU's DRAINL parameter.
  • DRESPL (SLDDRSPL) specifies whether the LU is willing to assume responsibility for deactivating sessions if a CNOS request is received specifying it as the responsible LU. VTAM handles this responsibility on behalf of the local LU. This DRESPL value is used when the LU is the target side of the negotiation. The application program can indicate either ALLOW or NALLOW.
    • B'1' (ALLOW) specifies that VTAM accepts a CNOS request specifying that the LU is responsible for deactivating sessions. If DRESPL=ALLOW is specified, VTAM performs no negotiation of the responsibility value carried in the CNOS request.
    • B'0' (NALLOW) specifies that VTAM does not accept a CNOS request specifying the LU is responsible for deactivating sessions. If DRESPL=NALLOW is specified, VTAM negotiates the responsibility value for the CNOS reply to be the sender of the CNOS request.

    For single-session connections, this field is not applicable.

    Note: When a CNOS request for all mode names is received from the partner LU, VTAM assigns the responsibility for deactivating sessions to the source side of the request.
  • DSESLIM (SLDDSESL) contains the value of the maximum session limits for the mode name group that VTAM is to accept when it receives a CNOS request, or when the LU initiates a CNOS request and did not specify any session limits for CNOS negotiation. The specified number can range from 0–32767.

    This session limit value is used only for CNOS negotiation. For single-session connections, this field is not applicable.

    Note: The value specified for the DSESLIM parameter must be greater than or equal to the value of the DMINWNL parameter plus the value of the DMINWNR parameter.
  • FQNAME (SLDFQNAM) contains the partner LU's fully qualified name. The FQNLEN field contains the actual length of the name. The fully qualified network name consists of an optional 1- through 8-byte network identifier and a 1- through 8-byte LU name. When present, the network identifier is concatenated to the left of the LU name, using a separating period and has the form NETID.name . When the network identifier is omitted, the period is omitted. The fully qualified name is available only after successful establishment of a session with the partner LU.
    Note: The partner LU provides its fully qualified network name in the Userdata subfield of the BIND. Because this name is optional information, it might not be provided. It is returned in the SLD only when it has been included in the BIND. It is not available until the LU receives a BIND response from the partner LU. If a CNOS request is negotiated with a partner LU that is single-session-capable, the name might not be available. In this case, the length field will be 0. Check the FQNLEN (SLDFQNLN) field to determine whether it is not 0 before checking the name.
  • FQNLEN (SLDFQNLN) indicates the length of the partner LU's fully qualified name, contained in the FQNAME field. The value of this field can range from 0–17. Zero is returned for the length if the fully qualified name is not available. See the note in the description for the FQNAME field for information about processing this field.
  • FREECNT (SLDFREEC) returns the number of sessions active with the partner LU that are currently available (free for use by a conversation).
  • MINWINL (SLDMCWL) returns the current number of parallel sessions of which the application program is guaranteed to be the contention winner. This is not the defined value, as provided on the APPL definition statement or the APPCCMD CONTROL=OPRCNTL, QUALIFY=DEFINE macroinstruction. It is the actual minimum contention-winner value supplied through an APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS macroinstruction or agreed upon during a CNOS negotiation. (The defined value is returned to the application program through the DMINWNL field.)
  • MINWINR (SLDMCWP) returns the current number of parallel sessions of which the partner LU is guaranteed to be the contention winner. This is not the defined value, as provided on the APPL definition statement or the APPCCMD CONTROL=OPRCNTL, QUALIFY=DEFINE macroinstruction. It is the actual minimum contention-winner value supplied through the APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS macroinstruction or agreed upon during a CNOS negotiation. (The defined value is returned to the application program through the DMINWNR field.)
  • NAMEUSE (SLDNMUSE) indicates how the application is identified to the partner LU. This field can indicate whether the name used is a user variable, a generic resource name, the application network name, or is unknown.
  • NMTYPE (SLDTYPE) indicates how the LU-mode table has classified the name for the partner LU. This field can indicate whether the name used is a supplied name, variant name, received name, disassociated name, or unusable.
  • PRSISTVL (SLDLPV) specifies whether the local LU accepts persistent-verification indicators on conversation requests.
    • B'0' (NO) specifies that the local LU does not accept persistent-verification requests.
    • B'1' (YES) specifies that the local LU does accept persistent-verification requests.
  • PRSISTVP (SLDPPV) specifies whether the partner LU accepts persistent-verification indicators on conversation requests.
    • B'0' (NO) specifies that the partner LU does not accept persistent-verification requests.
    • B'1' (YES) specifies that the partner LU does accept persistent-verification requests.
  • QALLOC (SLDQALLC) returns the number of queued ALLOCATE requests when a DEFINE or DISPLAY request completes.
  • SESSCAP (SLDSCAP) is the field in the DEFINE/DISPLAY session limits structure that indicates the session capability of the partner LU. The possible states that can be returned are:
    • B'01' (PENDING_SINGLE) indicates that VTAM is in the process of determining the session capability of the partner LU. The initial determination is that the partner LU is not parallel-session capable. This state changes to SINGLE after VTAM has confirmed the session capability. If this does not occur, VTAM deletes the LU entry in the LU-mode table associated with the partner LU.
    • B'00' (SINGLE) indicates VTAM has determined the partner LU to be single-session capable.

      When the partner LU is single-session capable (SLDSINGL field of the DEFINE/DISPLAY session limits structure), the partner name might be missing in the returned information because the BIND response has not returned. Check the FQNLEN (SLDFQNLN) field to be sure it is not 0 before checking the FQNAME (SLDFQNAM) field for the partner LU's fully qualified name.

    • B'10' (PENDING_PARALLEL) indicates that VTAM is in the process of determining the session capability of the partner LU. The initial determination is that the partner LU is parallel-session capable. This state changes to either SINGLE or PARALLEL after VTAM has confirmed the session capability. If this does not occur, VTAM deletes the LU entry in the LU-mode table associated with the partner LU.
    • B'11' (PARALLEL) indicates VTAM has determined the partner LU to be parallel-session capable.
  • SESSCNT (SLDSESSC) returns the session count for the number of sessions active currently with the partner LU that have the specified mode name.
  • SESSLIM (SLDSESSL) is the field in the DEFINE/DISPLAY session limits structure in which the session limit for the current mode name group is returned. This is not the defined session limit, as provided on the APPL definition statement or the APPCCMD CONTROL=OPRCNTL, QUALIFY=DEFINE macroinstruction. It is the actual session limit supplied through the APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS macroinstruction or agreed upon during a CNOS negotiation. (The defined session limit is returned to the application program through the DSESLIM field.)
  • SYNCLVL (SLDSYNCH) indicates the negotiated level of synchronization.
    • B'00' specifies that no synchronization level is supported.
    • B'01' specifies that the confirm synchronization level is supported.
    • B'10' specifies that the confirm and sync point levels are supported.
  • WINLCNT (SLDWINLC) returns the number of currently active sessions for which the application program is the contention winner.
  • WINRCNT (SLDWINPC) returns the number of currently active sessions for which the partner LU is the contention winner.