Maximizing IND$FILE 3270 host file transfer throughput (125881)

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 and by Host Integration Server 2000 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 and Host Integration Server 2000 is an 802.2 connection to the host via Token Ring (16 Mbps) or Ethernet (10 Mbps).

If you are using Host Integration Server 2004, the fastest link type would be an IP-DLC link service that connects to an IBM Gigabit Ethernet OSA-Express adapter. Depending on the network routes, bandwidth, and other factors, a channel connection may also be as fast or faster than an IP-DLC link service. As with previous versions of SNA Server and with Host Integration Server 2000, 802.2 DLC connections would be the next fastest link type.

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: 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: 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.