Maximizing IND$FILE 3270 Host File Transfer Throughput

• Microsoft SNA Server for Windows NT versions 2.0, 2.1, 2.11, 2.11 SP1, and 3.0

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 setup/advanced dialog in SNA Administrator.

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

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.

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

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. See the latest SNA Server third-party companion product catalog, ISVCAT.EXE, for a list of available products:

• ftp.microsoft.com in /BUSSYS/WINNT/SNA-PUBLIC