Resolving The Problem

Some HTML pages contain huge amount of data and images and thus users can often experience extended network access time and file downloading time because the requested data is transferred from the back-end server to WebSEAL and once more from WebSEAL to the browser. The solution for such a situation is utilizing both data compression and content caching.

Data Compression:
WebSEAL servers can be configured to compress data that is transferred over HTTP between the WebSEAL server and the browser. WebSEAL uses the gzip compression algorithm described in RFC 1952. Gzip is supported by all major browsers. HTTP compression in WebSEAL can be configured based on MIME-type, browser type, and protected object policies (POPs). Thus, Data Compression can be utilized to minimize the size of data transferred from WebSEAL to the browser.

Data compression can be configured in Webseal's configuration file as follows

[compress-mime-types]
mime_type = minimum_doc_size[:compression_level]

The minimum_doc_size value specifies policy regarding what size of documents will
be compressed. This value is an integer. Valid values are shown in the following
list:

- -1
When the minimum size is -1, documents of the specified MIME-type are never
compressed.
- 0
When the minimum size is 0, documents of the specified MIME-type are always
compressed.
- Integer greater than zero
When the minimum size is greater than zero, documents of the specified
MIME-type are compressed when the number of bytes in the response to
WebSEAL exceeds this integer value.

Any negative number other than -1 generates an error message.

The following example compresses all documents of a size greater than 1000 bytes:
[compress-mime-type]
*/* = 1000

The following set of entries disables compression for all images, disables
compression for CSS files, enables compression at level 5 for all PDF documents,
enables compression for HTML documents of size greater than 2000 bytes, and
enables compression for all other text documents, regardless of size:
[compress-mime-type]
image/* = -1
text/css = -1
application/pdf = 0:5
text/html = 2000
text/* = 0

Content Caching:
Data compression between WebSEAL and back-end servers is not supported. This is because WebSEAL does not perform filtering on compressed data. Content Caching can be utilized to minimize the size of data transferred from a back-end server to WebSEAL. Caching of Web content gives you the flexibility of serving documents locally from WebSEAL rather than from a back-end server across a junction. The content caching feature allows you to store commonly accessed Web document types in the WebSEAL server's memory. Clients can experience much faster response to follow-up requests for documents that have been cached in the WebSEAL server. Cached content can include static text documents and graphic images. Dynamically generated documents, such as database query results, cannot be cached.

You configure content caching in the [content-cache] stanza of the WebSEAL
configuration file. The following syntax applies:
<mime-type> = <cache-type>:<cache-size>


mime-type: Represents any valid MIME type conveyed in an HTTP
″Content-Type:″ response header. This value can contain an asterisk
(*). A value of */* represents a default object cache that will hold any
object that does not correspond to an explicitly configured cache.
Note that the asterisk here is a wildcard only for a MIME-type
directory, and its contents. The asterisk is not a wildcard for regular
expression matching.

cache-type: Specifies the type of storage medium to use for the cache. This release
of Tivoli Access Manager supports only ″memory″ caches.

cache-size: Specifies the maximum size (in kilobytes) to which the given cache
can grow before objects are removed according to a ″Least Recently
Used″ algorithm.

def-max-age: Specifies the maximum age (in seconds) if expiry information is
missing from the original response. If no value is provided, a default
maximum age of 3600 (one hour) will be applied.

Example:
[content-cache]
text/html = memory:2000
image/* = memory:5000
*/* = memory:1000