SNA Server 2.11 Performance Improvements for 3270/LUA Apps

• Microsoft SNA Server for Windows NT, version 2.11

SUMMARY

This article describes performance enhancements that were made to SNA Server service and client interfaces and how to obtain the update and how to derive benefits from this update if you are using third-party 3270 emulation products that work over the LUA variant of the SNA Server EIS interface.

MORE INFORMATION

The client-server protocol used to support the LUA-variant of the SNA Server 3270 Emulator Interface Specification (EIS) and LUA RUI interface has been enhanced to increase performance. The SNA Server service and Win32, Win3.x, OS/2 and MS-DOS RUI client interfaces have been updated. Down-level clients continue to function through the updated SNA Server service.

Also, the SNA Server 3270 applets include an additional performance improvement by requesting complete RUs rather than individual segments.

Any 3270 application that uses the LUA RUI interface, as well as any LUA RUI application, performs faster with this update applied. However, 3270 applications which use the LUA variant of the SNA Server EIS interface may require some further enhancements to take advantage of these performance improvements. These enhancements are described in the To Implement The Update section below.

To determine if a 3270 emulator uses the LUA-variant of the EIS interface, enable SNA Server 3270 message tracing and open a 3270 session. If byte 34 of Element #1 in the Open(SSCP) message is set to 0x01, then the LUA variant is being used. If byte 34 is set to 0x00, the LUA variant is not being used and no further application changes are necessary to implement the performance enhancements.

NOTE: The SNA Server 3270 applets use the LUA variant of the EIS interface. These 3270 applets have been updated to implement the performance enhancements described in this article.

Where Changes Were Made

The client-server message flow for the LUA-variant of the Emulator Interface was less efficient than it could be. The following explains two specific cases:

• When a Begin Bracket RU is received by the server, the server and client currently exchange a Status Control (BID) and acknowledgement before the data is sent to the client. Similarly, when a bracket officially ends, the server sends a Status (Betb) message. Both of these messages are redundant for the LUA interface, because the application processes the RH flags on the RUs NOT the FMI indicators.
• When a client acknowledges a data message, it has to wait for the server to acknowledge the acknowledgement with an ACKLUA message. This is so that the server can verify that the correct sequence number is provided on the response. This message has been removed by making the RUI application or 3270 EIS/LUA application responsible for tracking sequence numbers. The 3270 applet already acknowledges the correct sequence number, so the handshake is redundant.

To Implement the Update

To improve performance of your SNA Server 2.11 and the 3270 applets:

• Contact Microsoft Product Support for the update.

• Contact Microsoft Product Support for the update.
• Make the changes described below in the section titled Third-Party 3270 Emulation Products to support the performance enhancements available with the update.

 <snaroot>\system\SNASERVR.EXE - SNA Server service
 <snaroot>\system\TRCSERVR.EXE - Special traced version of SNA Server
                                 service
 <snaroot>\system\WINRUI32.DLL - Win32 client RUI DLL
 <winroot>\system\WINRUI.DLL   - Win 3.x client RUI DLL
 <snaroot>\ACSRUI.DLL          - OS/2 client RUI DLL
 <libs>\dos\dosacs.lib         - MS-DOS client RUI link library
 <libs>\dos\dtracs.lib         - Traced version of MS-DOS client RUI
                                 link library
 <snaroot>\SYSTEM\FMIS3270.DLL - Win32 3270 applet module
 <sna.win>\FMIS3270.DLL        - Win 3.x 3270 applet module

Third-Party 3270 Emulation Products

Third-party 3270 emulation products which work over the LUA variant of the SNA Server EIS interface require the following enhancements to support the performance enhancements available with the Microsoft update. Those 3270 emulation products or LUA applications that communicate over the LUA RUI interface do not require any modifications to obtain the performance improvements, because these changes are implemented by the RUI library.

Here is the information necessary for third party 3270 emulation vendors to implement these performance improvements:

• The LUA version number is contained in the Open(SSCP) request message at dataru[40] (dataru[39] is reserved and should be set to 0). The following are the supported values of the LUA version:

      - 0x01 - the original (that is, unmodified) LUA version of the EIS.
  

      - 0x02 - the new version incorporating the API changes below.
  

  If the emulator specifies a version greater than that supported by the current SNA Server, the server negotiates the version down on its Open (SSCP) response (see below). Modifications to the API are incremental; any emulator supporting any future version X must support all the version X-1 features.

  Note that startd must be set to 41 or greater. If startd is less than 41, the emulator is indicating support for version 1 only.

• SNA Server returns the version number to be used on the Open (SSCP) response message in the lower 7 bits of dataru[40] with the top bit always set to b'1'. If the emulator receives an Open (SSCP) response message with startd less than 41 or with the top bit of dataru[40] clear, it must assume that the node supports version 1 of the LUA version of the EIS only.
• The Node continues to sent Status-Control (BID) messages when an explicit SNA BID request is received on the session (the RBI flag is set in the Application Flags bytes in the message header).
• An emulator specifies that it is responsible for sequence number checking by setting the ackqual field of the Status-Acknowledge message to ACKLUA instead of ACKPOS. This causes the Node to generate a positive response on the session without returning a Status-Acknowledge (ACKLUA) message to the emulator. Note that if the emulator provides an incorrect sequence number no indication is sent to the emulator and no response is sent on the session. This change does not apply to negative responses or Status-Control-Acknowledge messages, for which emulators continue to receive Status-Acknowledge(ACKLUA) messages.

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