Microsoft KB Archive/185097

= SNA Server and Host Integration Server do not support compression across 3270/FMI interface =

Article ID: 185097

Article Last Modified on 12/4/2007

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APPLIES TO


 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 4.0 Service Pack 4
 * Microsoft Host Integration Server 2000 Standard Edition
 * Microsoft Host Integration Server 2000 Service Pack 1
 * Microsoft Host Integration Server 2004 Standard Edition

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This article was previously published under Q185097



SUMMARY
Some 3270 emulators, such as IBM's Personal Communications/3270, support SNA session-level compression that allows the 3270 data sent between the 3270 emulator and the host to be compressed. This compression is also known as Length-Checked Compression (LCC).

Microsoft SNA Server 4.0 and Microsoft Host Integration Server and later support SNA session-level compression between the SNA or Host Integration Server and a Host (Mainframe or AS/400).

This feature allows the same type of data compression that is offered by those 3270 emulators that support SNA session-level compression, so it can be used in those instances where SNA session-level is necessary.



MORE INFORMATION
Neither SNA Server nor Host Integration Server support SNA session-level compression (that is, LCC) for 3270 sessions across its native Function Management Interface ([FMI], also known as Emulator Interface Specification [EIS]). Compression is not supported across the FMI interface because the SNA Server service frequently has to segment the FMI data that it receives from the 3270 emulator into smaller RUs to be sent to the host. If the data were compressed, SNA Server would not be able to correctly segment the data.

In addition, the LUA interfaces (RUI and SLI) do not support the ability to negotiate the use of SNA session-level compression.

SNA session-level compression only needs to be used in certain instances. These may include the following:
 * Slow link speeds between the SNA Server and the host.
 * Links whose costs are based on traffic volume.

In most cases, the link speed (that is, the bandwidth) between the 3270 clients and the SNA or Host Integration Server is not sufficiently slow to warrant the compression of the data between the client and the SNA or Host Integration Server.

