Maximizing IND$FILE 3270 Host File Transfer Throughput

ID: Q125881

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

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. 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-DOCS

Additional query words: prodsna ind$file 3270 file transfer

Keywords : kbnetwork kbtool sna3rdparty sna3270 snachannel snadlc snasdlc sna211 sna211sp1 sna211sp2 sna3 sna3sp1 sna3sp2 sna3sp3 sna4 sna4sp1 sna2 sna21
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
Platform : WINDOWS
Issue type :