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Q125881: Maximizing IND$FILE 3270 Host File Transfer Throughput

Article: Q125881
Product(s): Microsoft SNA Server
Version(s): WINDOWS:2.0,2.1,2.11,2.11 SP1,2.11 SP2,3.0,3.0 SP1,3.0 SP2,3.0 SP3,4.0,4.0 SP1
Operating System(s): 
Keyword(s): kbnetwork kbtool kbsna211sp1 kbsna211sp2 kbsna300sp1 kbsna300sp2 kbsna300sp3 sna4 kbsna
Last Modified: 10-JUL-2002

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The information in this article applies to:

- Microsoft SNA Server, versions 2.0, 2.1, 2.11, 2.11 SP1, 2.11 SP2, 3.0, 3.0 SP1, 3.0 SP2, 3.0 SP3, 4.0, 4.0 SP1 
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SUMMARY
=======

Windows NT SNA Server 3270 and other third-party 3270 emulators support host
file transfer using the host IND$FILE interface. There are three ways you can
improve performance:

- Choosing a Fast SNA Link Interface to the Host

- Maximizing the SNA Link Frame Size

- Maximizing the 3270 Structured Field RU Size

Choosing a Fast SNA Link Interface to the Host
----------------------------------------------

The fastest link type supported by SNA Server is a channel connection to the
host. SNA Server 2.11 and later includes built-in support for channel adapters.
Please refer to the SNA Server Companion Product Catalog for more details on
available channel adapter support. Note: SNA Server 2.1 supports channel
connections via third-party drivers.

If a channel connection is not possible, the next fastest link type supported by
SNA Server is an 802.2 connection to the host via Token Ring (16 Mbps) or
Ethernet (10 Mbps).

Maximizing the SNA Link Frame Size
----------------------------------

The maximum frame size supported by SNA Server and the host varies depending on
the link type. The host frame size is configured in the MAXDATA= parameter in
the PU definition in VTAM. This setting should match the "Max BTU size" in the
SNA Server Connection configuration dialog in SNA Admin/Manager.

Here are the maximum frame sizes supported (in bytes):

  802.2 Token Ring connection (16 Mbps):      16393
  802.2 Token Ring connection (4 Mbps):        4096
  802.2 Ethernet connection:                   1493

  IBM SDLC/MPAA adapter or Microgate adapter:   521

The maximum frame size provided by third-party SNA Server link support depends on
the third-party interface being used.


Maximizing the 3270 Structured Field RU Size
--------------------------------------------

Maximizing the SNA RU size reduces end-to-end acknowledgments at the 3270
application level. An RU is split into multiple messages if the frame size is
smaller.

First, the query bit on the LU definition at the host must be enabled in order to
support structured field file transfer. This is enabled in bit 0 (the high order
bit) on byte 1 in the PSERVIC parameter which you can configure in the MODEENT
on the 3270 LU's DLOGMODE mode entry:

  PSERVIC=X'0280xxxx...

  Byte 0 is the LU type (02 in this example)
  Byte 1 is used by VSCS and needs to be set as follows:

  80 - Device supports extended data stream capability. It supports
  write structured field (WSF) and read partition query (Query)
  structured field.

Otherwise, screen-mode transfer is used, limiting the data RU size to 1920
bytes.

The RU size supported by the host is configured in the RUSIZES=LU mode entry
(MODEENT). Here are common values used:

  8787 = 1024
  8888 = 2048
  8989 = 4096
  8A8A = 8192
  8B8B = 16384
  8C8C = 32768

The RU size is computed as follows: RUSIZES = MNMN, where the RU size = M*2^N.
This specifies the maximum length of data (request units) in bytes that the
primary or secondary can send to each other. The leftmost two digits apply to
the secondary (SNA Server) logical unit, and the rightmost two digits apply to
the primary (host) logical unit. If set to 00, then the default size (no limit
on the RU size) is used.

Within the 3270 emulator, the structured field file transfer RU size must be
specified in the file transfer configuration. Within SNA Server 3270, this is
set in the Packet Size field within the 3270 File Transfer dialog box. The
maximum value is 32767.

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

While the SNA link interface and frame size are often not adjustable, maximizing
the 3270 structured field file transfer RU size can provide dramatic performance
improvements.

However, IND$FILE is not an efficient file transfer method. For higher throughput
host file transfer, an LU 6.2-based file transfer product should be considered.


Additional query words: prodsna ind$file 3270 file transfer

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Keywords          : kbnetwork kbtool kbsna211sp1 kbsna211sp2 kbsna300sp1 kbsna300sp2 kbsna300sp3 sna4 kbsna400sp1 
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ300 kbSNAServ200 kbSNAServ211 kbSNAServ400 kbSNAServ210 kbSNAServ211SP1 kbSNAServ211SP2 kbSNAServ300SP3 kbSNAServ300SP1 kbSNAServ400SP1 kbSNAServ300SP2
Version           : WINDOWS:2.0,2.1,2.11,2.11 SP1,2.11 SP2,3.0,3.0 SP1,3.0 SP2,3.0 SP3,4.0,4.0 SP1

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