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In order for a file to be transmitted using HTTP compression, the following two conditions must be true:
The client must support a compression scheme used by IIS.
IIS must have already compressed the file, which will be stored in a temporary folder.
How to Determine if the Client Supports Compression
View the client's HTTP GET Request to see if it specifies a compression value in the Accept-Encoding header that IIS supports. For example, Internet Explorer 5.0 sends the following header:
Accept-Encoding: gzip, deflate
Note: Both the Gzip and Deflate compression schemes are supported by IIS.
For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
252876 How to View HTTP Data Frames Using Network Monitor
How to Determine if the File Is Compressed
Open the temporary folder that stores the compressed version of files (C:\WINNT\IIS Temporary Compressed Files by default). In order to avoid duplicate file names, each file that is compressed, is renamed by appending characters to the beginning of the file name.
If a compressed, renamed version of the file in question exists, then it is sent to clients that support the compression scheme.
Note: The temporary folder is specified on the Service tab in the WWW Service Master Properties for ComputerName dialog box in the IIS snap-in.
(c) Microsoft Corporation 2000, All Rights Reserved. Contributions by Kevin Zollman, Microsoft Corporation.