Configuring for host compression when you use non-extended BINDs

In most cases, Microsoft SNA Server session-level compression is negotiated between SNA Server or Microsoft Host Integration Server and the host by using an extended BIND. It is possible to use SNA Server session-level compression when the host sends a non-extended BIND to SNA Server.

If the host sends a non-extended BIND requesting session-level compression, the following configuration is required on SNA Server and Host Integration Server to make sure that its BIND response indicates that the request for compression is accepted.

3270 Compression

1. The Compression Type option on the System Identification tab in the Connection Properties dialog box must be set to LZ9.
2. The Use Compression option in the 3270 LU Properties dialog box must be enabled for 3270 sessions that require compression.

LU 6.2 Compression

1. The Compression Type option on the System Identification tab in the Connection Properties dialog box must be set to either RLE or LZ9.
2. The Maximum Send Compression option on the Compression tab in the APPC Mode Properties dialog box must be set to RLE.
3. The Maximum Receive Compression option on the Compression tab in the APPC Mode Properties dialog box must be set to LZ9.

Note If SNA Server or Host Integration Server initiates a BIND request for an LU 6.2 session in which compression is configured, it send an extended BIND.

A Primary Logical Unit (PLU) level of compression support is indicated in bits 6 and 7 of Byte 25 of the BIND. The following is an explanation of these 2 bits and how the level of compression is indicated by their values:


In addition to the setting of the length-checked compression bits of Byte 25, an extended BIND includes additional information related to compression.

A BIND is considered an extended BIND when it includes a Fully Qualified PCID (X'60') control vector. When compression is requested and/or enabled, an extended BIND also includes a Length-Checked Compression (X'66') control vector. The Length-Checked Compression control vector contains the information needed to allow the compression level to be negotiated between the PLU and Secondary Logical Unit (SLU).

The following compression levels are available when you are using non-extended BINDs as defined in the IBM SNA Formats (GA27-3136) manual:


When SNA Server and Host Integration Server receive a non-extended BIND from the host that indicates PLU supports or requests compression, there is no way to determine what level of compression (LZ9 or RLE) the PLU supports. Because either compression level can be used, SNA Server and Host Integration Server 2000 must be configured to handle both compression levels. For 3270 compression, this means that LZ9 compression must be set on the host connection properties. For LU 6.2 compression, LZ9 compression must be selected for Maximum Receive Compression in the APPC mode definition that will be used by the application.

LZ9 compression provides for a higher level of compression that also includes RLE compression. If SNA Server or Host Integration Server is configured to support LZ9 compression, it can support RLE compression as well.

SNA Server session-level compression is discussed in further detail in the IBM SNA Formats (GA27-3136) manual. For more information, please see the following topics:

• Request/Response Headers (RHs)
• BIND RU in the Request/Response Units (RUs)
• Fully Qualified PCID and Length-Checked Compression control vectors in the Common Fields