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Q138834: Improvements for EIS/3270 and APPC Resource Location

Article: Q138834
Product(s): Microsoft SNA Server
Version(s): WINDOWS:2.11
Operating System(s): 
Keyword(s): kbnetwork kbprogramming
Last Modified: 13-JUN-2001

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The information in this article applies to:

- Microsoft SNA Server, version 2.11, on platform(s):
   - the operating system: Microsoft Windows NT 
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SYMPTOMS
========

This article describes how the SNA Server client server interface locates an
available LU for both APPC and EIS/3270 applications, both with and without
Service Pack 1 installed.

Microsoft has updated the following files. Service Pack 1 is planned to be
released in December 1995. To obtain these files before Service Pack 1 is
released, contact Microsoft Product Support Services. Service Pack 1 includes
the following modified files:

  Operating System     Modified Files
  ---------------------------------------------------------------
  Windows NT           SNABASE.EXE, SNACFG.DLL, SNADMOD.DLL, WAPPC32.DLL
  Windows 95           SNADMOD.DLL, WAPPC32.DLL
  Windows 3.x          WDMOD.DLL, WINAPPC.DLL

STATUS
======

This feature is included in the latest U.S. Service Pack for SNA Server for
Windows NT, version 2.11. For information on obtaining the Service Pack, query
on the following word in the Microsoft Knowledge Base (without the spaces):

  S E R V P A C K

MORE INFORMATION
================

EIS/3270, Without Service Pack 1 Installed
------------------------------------------

Over the sponsor connection, the EIS/3270 application makes a sepdcrec() call to
acquire a list of the LUs/pools that are assigned to the client's user record.
On a connect request to open a session, the application issues an OPEN SSCP
request on the chosen LU/Pool name. The underlying DMOD (part of the client
server interface) attempts to locate the server that can house this available LU
by connecting to each server in the client's local service table one by one
until the specified LU/Pool is satisfied. It must do this because the local
service table does not contain any LU/Pool information; it contains only server
names.

APPC, Without Service Pack 1 Installed
--------------------------------------

During the TP_START request and ALLOCATE verb processing that a TP does to get a
conversation, the underlying DMOD (part of the client server interface) attempts
to locate the server that houses this available LU by connecting to each server
in the client's local service table one by one until the specified LU-LU pair is
satisfied. It must do this because the local service table does not contain any
APPC LU information; it contains only server names.

EIS/3270, With Service Pack 1 Installed
---------------------------------------

The client still makes the normal sepdcrec() call to acquire a list of the
LUs/pools that are assigned to the client's user record. As part of the OPEN
SSCP message processing, the SNA Server client software sends a new RPC request
(RPC_LU_SERVER_LIST) to the SNA Server that is supporting the client computer's
sponsor connection. The requested LU name from the OPEN SSCP is part of the RPC
request. The sponsor server returns a list of the servers who can possibly
support the requested LU. If the LU is a dedicated LU, the list has only one
server name. If it is a POOL the list may have up to 50 server names. After this
RPC response, the resource locating continues normally except that the client
tries (in random order) only the servers whose names are in the LUs server list.
In general, the client tries only the servers that can actually support the LU
resource.

APPC, With Service Pack 1 Installed
-----------------------------------

The RPC request is sent as part of the TP_START request and ALLOCATE verb
processing. In both cases, the server returns the list of servers where the
local or remote LU Alias is configured. The rest is similar to 3270 resource
location.

In both the EIS/3270 and the APPC, the RPC request is sent only once per LU. The
SNA Server client interface cashes the LU/Server information internally. In
Windows NT and Windows 95, the cache is flushed when the application exits. In
Windows 3.x, the cache is flushed when the client server piece (Wnap.exe)
terminates.

NOTE: If the sponsor server is not running SNA Server 2.11 with Service Pack 1
installed, the client DMOD sends only one RPC request. After it gets the "not
supported" error it does not try again.

If the RPC request fails for any reason, for example if the sponsor does not
support the new RPC request, the DMOD uses the old resource locating algorithm.

No changes are required to existing emulators, including the 3270 application
that ships with SNA Server.

Additional query words: prodsna

======================================================================
Keywords          : kbnetwork kbprogramming 
Technology        : kbAudDeveloper kbSNAServSearch
Version           : WINDOWS:2.11
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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