How to Determine if APPC LU Partnerships are Required

• Microsoft SNA Server, versions 3.0, 3.0 SP1, 3.0 SP2

SUMMARY

When using SNA Server 3.0, which supports dynamic partnership of local and remote APPC LU's to an APPC mode (in other words, LU/LU/mode partnership), it's not necessary to preconfigure LU/LU/mode partnership in the SNA Server configuration file in order to use these LU's. Under SNA Server 2.x, all APPC LU partnerships had to be defined ahead of time using SNA Admin before the LU's could be used.

NOTE: The SNA Server 3.0 and 3.0 SP1 Manager tool does not support the ability to configure LU/LU/mode partnerships, though this feature has been reimplemented in 3.0 Service Pack 2 within the APPC mode definition. The Snacfg.exe command line tool has always supported the ability to define LU/LU/mode partnerships.

In most cases, explicit LU/LU/mode partnerships do not have to be defined. If APPC LU/LU/mode partnerships are not defined in the SNA Server 3.0 configuration file, LU6.2 session activation is deferred. This can cause the following problems or side effects:

1. APPC or CPIC applications which attempt to allocate an LU6.2 conversation without waiting for an LU6.2 session to be activated may fail to allocate a conversation. An example of such an application is the Sybase/MDI DB2 Database Gateway.

   See below for more information about this failure.

2. APPC applications which rely on LU6.2 session information to be returned by the APPC DISPLAY verb may fail to work. An example of such an application is IBM CICS for Windows NT and Windows 95. For more information about this problem, see the following article in the Microsoft Knowledge Base:

         ARTICLE-ID: Q171994    
         TITLE: IBM CICS For Windows NT Stops Working On SNA Server 3.0 
   
   

3. If an APPC mode is configured with any autoactivated sessions, LU6.2 sessions do not activate until the first APPC/CPIC application requests a conversation over an APPC LU/LU pair and requests this APPC mode. This simply defers LU6.2 session autoactivation, which is typically configured to force session activation when SNA Server starts. By autoactivating an LU6.2 session, this can improve performance for the first APPC or CPIC application which attempts to allocate a conversation over this LU/LU/mode partnership.

MORE INFORMATION

The local and remote LU's defined in SNA server work in pairs. The local APPC LU is assigned to a server and the remote APPC LU is assigned to the connection. SNA Server uses dynamic partnering to create any possible LU partnerships on demand when local and remote LU's and modes recognize each other.

With dynamic APPC partnering, an administrator configures remote LU's, but normally does not need to partner them with local LUs. SNA Server will automatically partner the LUs when needed.

APPC applications, such as Sybase/MDI DB2 Gateway, rely on availability of auto- started APPC conversations on LU to LU pairs. Such applications typically use the Allocate qualifier AP_IMMEDIATE (which is described in the APPC Programmer's reference) to open a conversation only if one of the auto-activated conversations is available for use; these applications will not cause an additional conversation to be allocated. To support applications which specify the AP_IMMEDIATE qualifier, the LU pairs should be partnered manually.

If an APPC application which specifies the AP_IMMEDIATE qualifier does not have the Local and Remote LU's explicitly partnered with a mode , it will fail to build a conversation to the remote TP and post the following error message in the NT Event log from where the application is running.

APPC local conversation start failed:

   Primary_rc   = 0014 (AP_UNSUCCESSFUL) 
   Secondary_rc = 00000000
   TP_ID        = 0000000080097F00
   Dest TP name = D9C5C3E5E3D7
   LU alias     = SENDLU  
   PLU alias    = RECVLU  
   Mode name    = 7BC9D5E3C5D94040
 

The SNA trace utility is a tool that can be used to track the activities of the API's being issued by the application and therefore can be used to determine which qualifier is specified in the Allocate or Send_Conversation verb posted by the invokeable TP. Please see the SNA Server Administration guide for details on how to perform an APPC application trace.

The return control qualifier which is specified by the TP can be located at offset 28 from the beginning of the request. See Figure 1 below. In this case, a 0x01 is specified, which represents the AP_IMMEDIATE constant. Figure 2 depicts other qualifier which can be used here as well. The example here is using the mapped conversation type.

   FIGURE 1.
   ---------
   MC_SEND_CONVERSATION request

   Type:Sync                                  VerbID:00001400

   ---- Verb Parameter Block at address 0041D840 ----
   18000100 00000000 00000000 00000000     <................>
   F0177F00 70197F00 00000000 01000000     <0.[ASCII 166].p.>
   00000000 00000000 52454356 4C552020     <........RECVLU  >
   7BC9D5E3 C5D94040 D9C5C3E5 E3D74040     <{INTER@@RECVTP@@>
   40404040 40404040 40404040 40404040     <@@@@@@@@@@@@@@@@>
   40404040 40404040 40404040 40404040     <@@@@@@@@@@@@@@@@>
   40404040 40404040 40404040 40404040     <@@@@@@@@@@@@@@@@>
   40404040 40404040 00000000 00000000     <@@@@@@@@........>
   00000000 00000000 00000000 00000000     <................>
   00000000 00000000 00000000 00000000     <................>
   00000000 00000000 00000000 00000000     <................>
   00000000 00000000 00000200 E00D0C01     <................>

   Figure 2.
   ---------
   AP_WHEN_SESSION_ALLOCATED         0x00
   AP_IMMEDIATE                      0x01
   AP_WHEN_SESSION_FREE              0x02
   AP_WHEN_CONWINNER_ALLOCATED       0x03                         
   AP_WHEN_CONV_GROUP_ALLOCATED      0x04